Cinchona

What is Cinchona?

Cinchona bark must contain at least 6.5 percent total alkaloids to meet the European Pharmacopoeia monograph, and only 30 to 60 percent of that total is quinine-type alkaloid. Everything else about this ingredient follows from that one specification, because cinchona is the bark of a South American tree whose entire commercial history rests on a single molecule it makes in variable amounts.

The genus belongs to the Rubiaceae, the coffee family. Carl Linnaeus named it Cinchona in 1742 after a story about the Countess of Chinchón, vicereine of Peru in 1638, and he wrote the name without the first h. Clements Markham and others later argued for correcting it to Chinchona. The misspelling stuck, so the plant that supplies the world's quinine is named after a mangled Spanish title attached to a legend historians have never verified.

Pierre Joseph Pelletier and Joseph Bienaimé Caventou isolated quinine and cinchonine from the bark in 1820 in Paris. That isolation is the reason cinchona and quinine are not interchangeable words. Quinine is one compound with a measurable plasma concentration and an approved drug product behind it. Cinchona is a bark containing that compound alongside at least three structurally related alkaloids, at concentrations that vary by species, by tree age, by part of the bark and by growing region. A total synthesis route was published in 1944 and never displaced agriculture. Plantation bark remains the only economically practical source of quinine, and quinine remains on the World Health Organization Model List of Essential Medicines.

Common Names

• Cinchona bark, Peruvian bark, Jesuit's bark, cardinal's bark

• Quina, quina roja, quinquina, china bark, calisaya bark

• Red cinchona (from Cinchona pubescens), yellow cinchona (from Cinchona calisaya)

• China officinalis, the homeopathic designation, which is a different preparation entirely

Primary Active Compounds

• Quinine, the levorotatory antimalarial quinoline methanol. In four commercial bark samples bought from pharmacies in Innsbruck, Austria and analyzed by Murauer and Ganzera (Journal of Chromatography A, 2018), quinine ran 1.59 to 1.89 percent of dry bark.

• Quinidine, the diastereomer of quinine and a Class Ia antiarrhythmic in its own right. It is the alkaloid responsible for most of cinchona's QT interval concern.

• Cinchonine, 1.87 to 2.30 percent in the same four samples, slightly exceeding quinine in every one of them.

• Cinchonidine, 0.90 to 1.26 percent in those samples.

• Quinic acid, cinchotannic acid and bitter glycosides, which carry the taste and the traditional digestive use.

• Total of the three quantified alkaloids in that study ranged 4.75 to 5.20 percent. That number sits below the Ph. Eur. minimum of 6.5 percent, and the gap is one of assay scope rather than substandard bark: the method resolved six alkaloids but quinidine, dihydroquinine and dihydroquinidine gave peaks too small to quantify, so a three-alkaloid subtotal is being compared against a total-alkaloid specification. The two figures are not comparable.

Key Note

Cinchona ledgeriana bark grown on Dutch Java plantations yielded 8 to 13 percent quinine, roughly five times what a generic pharmacy sample contains. The species on a capsule label, if one is named at all, is usually Cinchona officinalis L., the Linnaean type species, which grows in a small region of Ecuador and has minor medicinal significance next to C. calisaya Wedd., C. pubescens Vahl and C. ledgeriana. A label naming the historically famous species is naming the commercially weak one.

Primary Functions & Benefits

Cinchona has four distinct claimed functions, and the evidence behind them differs by orders of magnitude.

Antimalarial activity. Real and well quantified, but it belongs to isolated quinine at pharmaceutical doses, not to bark. Quinine kills the blood stages of Plasmodium falciparum, P. vivax, P. ovale and P. malariae. The CDC treatment table for uncomplicated P. falciparum malaria acquired in chloroquine-resistant areas gives quinine sulfate 542 mg base, which is 650 mg salt or two 324 mg capsules, three times daily for 7 days, paired with doxycycline 100 mg twice daily for 7 days.

Muscle cramp reduction. Quinine reduces cramp frequency modestly. The Cochrane review by El-Tawil and colleagues (CD005044.pub3, published April 5, 2015, searches through October 2014) pooled 23 randomized trials and 1,586 participants across all five comparisons, at doses of 200 to 500 mg daily, most commonly 300 mg. The placebo comparison, which is where every efficacy number below comes from, covered 20 trials and 1,140 participants. Over two weeks, cramp number fell 28 percent against placebo on low quality evidence, cramp intensity fell 10 percent on moderate quality evidence and cramp days fell 20 percent on low quality evidence. Cramp duration did not change.

Bitter digestive stimulation. The German Commission E monograph approves cinchona bark for loss of appetite and dyspeptic complaints including flatulence and bloating. The mechanism is bitter receptor stimulation of gastric secretion and is shared by gentian, wormwood and every other classical bitter. No dose finding trial in humans supports a specific cinchona amount for this use.

Flavoring. Quinine is the defining bitter of tonic water and of the quinquina aperitifs. This is a food additive function, regulated separately from both drug and supplement law, and it is the only cinchona use in which the quinine content is capped by regulation.

What cinchona does not do, on any published human evidence: treat viral respiratory infection, prevent malaria as a supplement dose, correct any nutritional deficiency, or produce the antimalarial effect of quinine at the amounts found in capsules.

Forms & Standardization

This is where the gap between cinchona the botanical and quinine the drug becomes arithmetic.

Whole and cut bark. Sold loose for decoction. Ph. Eur. grade requires a minimum 6.5 percent total alkaloids with quinine-type alkaloids at 30 to 60 percent of that total. Because 6.5 percent is a monograph minimum and not a maximum, that fixes a quinine-type floor of about 1.95 percent but sets no upper bound at all: bark assaying 10 percent total alkaloids at the top of the 30 to 60 percent band would carry about 6 percent quinine-type alkaloid. Bark sold outside pharmacopoeial channels is not held to this and is rarely assayed at all.

Powdered bark capsules. A representative US product sells Cinchona officinalis bark powder at 450 mg per capsule with a 1,350 mg serving of three capsules and no standardization statement on the label. At the Murauer and Ganzera measured range of 1.59 to 1.89 percent quinine, that serving delivers roughly 21 to 26 mg. At 3.9 percent quinine-type, the figure implied by the Ph. Eur. minimum sitting at the top of the 30 to 60 percent band, it would reach about 53 mg, and richer bark would carry more than that. Nobody buying it knows which.

Fluid extracts and tinctures. Commission E lists a tincture standardized to 4 to 5 percent total alkaloids at 0.6 to 3 g daily, and an extract at 15 to 20 percent total alkaloids at 0.15 to 0.6 g daily. These are the only cinchona dosage forms in common use anywhere with a stated alkaloid specification.

The alkaloid salts, which are drugs and not supplements. Quinine sulfate, quinine dihydrochloride, quinine hydrochloride, quinine bisulfate and quinine gluconate. Quinidine sulfate and quinidine gluconate are the antiarrhythmic salts of the diastereomer. Salt weight and base weight differ, which is why CDC writes both: 650 mg of quinine sulfate salt is 542 mg of quinine base.

What a pharmaceutical dose looks like. Qualaquin was quinine sulfate 324 mg per capsule, approved by FDA on August 12, 2005 under NDA 021799. That brand is now listed as discontinued, and the same 324 mg capsule is marketed as a generic under three active ANDAs held by Teva, Lupin and Ingenus. The labeled regimen for adults 16 and over is 648 mg every 8 hours for 7 days, which is 1,944 mg of salt and roughly 1,614 mg of base per day, for 13,608 mg of salt across the course.

What a supplement contains against that. A 1,350 mg bark serving at 21 to 53 mg of quinine is about 1 to 3 percent of a single day of antimalarial dosing. It is also below the 200 to 300 mg quinine sulfate per tablet that the withdrawn over-the-counter leg cramp products carried. A cinchona capsule is not a covert quinine tablet, and that is not reassurance. It is an unmeasured fraction of one, and that unmeasured quality is the problem, because the reactions that killed people are not dose dependent.

Food Sources

Quinine is the rare botanical alkaloid with a hard numerical ceiling in food law, and the ceiling is the most useful number in this issue.

Tonic water. Under 21 CFR 172.575, quinine as the hydrochloride or sulfate salt may be used in carbonated beverages only, not to exceed 83 parts per million calculated as quinine, and its presence must be declared prominently either in the product name or as a separate declaration. Harcher and colleagues measured Canada Dry and Schweppes tonic water by fluorescence spectroscopy (Methods and Protocols, 2025, volume 8, issue 1, article 5) at 64.60 ± 3.66 and 64.50 ± 2.68 mg per liter respectively, in an undergraduate teaching exercise where five student groups each ran the assay. A 12 fluid ounce can, 355 mL, therefore carries about 23 mg of quinine. A 200 mL mixer pour carries about 13 mg.

What that comparison means. One 12 ounce tonic water delivers about as much quinine as three 450 mg cinchona bark capsules, at a known concentration, under a legal cap, with mandatory disclosure. The capsules have no cap and no disclosure. Donovan and colleagues (Food and Chemical Toxicology, 2003) gave 11 healthy volunteers aged 26 to 54 a full liter of tonic water containing 80 mg of quinine and found no CYP2D6 inhibition, with dextromethorphan metabolic ratios of 0.032 ± 0.067 against 0.013 ± 0.028 for control, P greater than 0.05.

Bitters and aperitifs. The quinquina category is built on cinchona: Dubonnet, Byrrh, Cocchi Americano, Lillet and the amaro family. Schweppes Bitter Lemon and Dubonnet both appear by name in the University of Oklahoma drug-induced thrombotic microangiopathy registry as documented quinine exposure sources. Cocktail bitters made from cinchona bark are dosed in dashes and contribute single-digit milligrams at most.

European limits. Quinine salts are authorized flavoring substances in the EU under Regulation (EC) No 1334/2008, where the restrictions column of the Annex I Union list caps them at 100 mg/kg in non-alcoholic beverages, 100 mg/kg in alcoholic beverages and 250 mg/kg in spirit drinks, expressed as quinine base and counted across the three authorized quinine salts combined. All three limits sit above the US ceiling.

Is food intake sufficient? For flavor, obviously. For any therapeutic purpose, no, and that is the point rather than a criticism. Liles and colleagues (American Journal of Hematology, 2016, volume 91, issue 5, pages 461 to 466) reviewed 114 published articles describing 142 patients with definite or probable quinine-caused acute reactions, and 28 of them, 20 percent, were exposed through quinine-containing beverages rather than pills.

Who Should Take Cinchona

The honest list is short.

• Nobody needs cinchona nutritionally. It supplies no vitamin, mineral, amino acid or fatty acid in meaningful quantity.

• People treating malaria should be taking quinine sulfate under prescription, not bark. Quinine sulfate 324 mg capsules are the only FDA approved quinine products in the United States, indicated only for uncomplicated P. falciparum malaria; the Qualaquin brand is discontinued and the product is now supplied as a generic. Bark at supplement doses does not reach therapeutic plasma concentrations, and undertreated falciparum malaria kills.

• Adults using a traditional bitter before meals for appetite or dyspepsia are the only group with a plausible low-dose use, and Commission E sets that at 1 to 3 g of dried bark daily. Gentian root and wormwood provide the same bitter stimulus without quinine alkaloids, and that substitution is worth making.

• Nobody should take cinchona for nocturnal leg cramps. This is the use the capsules are marketed for and the one use with a documented body count, so read the next two sections before anything else. The American Academy of Neurology review by Katzberg, Khan and So (Neurology, 2010) rated quinine derivatives Level A for effectiveness, with two Class I trials showing 25 and 37 percent reductions in cramp frequency, and still recommended against routine use, restricting consideration to prescription quinine in cramps that are very disabling, where no other agent relieves symptoms and side effects are carefully monitored. That pathway runs through a physician and a measured drug, neither of which a bark capsule offers.

Who Should AVOID or Use Caution

Contraindications

The quinine sulfate label lists these as contraindications, and every one of them applies to a bark whose quinine content is unknown:

• Prolonged QT interval, congenital or acquired.

• Glucose-6-phosphate dehydrogenase (G6PD) deficiency, because of hemolysis risk.

• Known hypersensitivity to quinine, including any prior episode of thrombocytopenia or hemolytic uremic syndrome attributed to quinine or to tonic water.

• Known hypersensitivity to mefloquine or quinidine, which cross-react.

• Myasthenia gravis, because quinine reduces motor end plate excitability and can precipitate respiratory failure.

• Optic neuritis, because quinine is directly retinotoxic.

Pregnancy is not on that list. The quinine sulfate label classes quinine as Pregnancy Category C, to be used only if the potential benefit justifies the risk. It is Commission E, separately, that contraindicates cinchona bark in pregnancy, and also in gastrointestinal ulceration and in children under 12.

Use Caution

• Anyone with a bleeding disorder, recent thrombocytopenia of any cause, or unexplained bruising.

• Anyone with chronic kidney disease. Quinine half-life extends to roughly 26 hours in severe renal impairment against 9.7 to 12.5 hours in healthy adults.

• Older adults taking multiple medications. Quinine is metabolized mainly by CYP3A4 with contributions from CYP1A2, 2C8, 2C9, 2C19, 2D6 and 2E1, and it inhibits CYP2D6 and P-glycoprotein at antimalarial concentrations.

• Anyone with existing hearing loss or tinnitus, since quinine's concentration-dependent high-tone hearing loss starts from that baseline.

• Diabetics and anyone prone to hypoglycemia. Quinine stimulates pancreatic insulin release. In SEAQUAMAT, hypoglycemia carried a relative risk of 3.2 (95 percent CI 1.3 to 7.8, p = 0.009) in the quinine arm against artesunate.

Critical Safety Point

Quinine-induced immune thrombocytopenia and quinine-induced hemolytic uremic syndrome are not dose-related. They are antibody-mediated, they can follow a single small exposure in a sensitized person, and they can arrive within hours. The Oklahoma registry lists quinine with 44 patients at the highest evidence level and identifies it as the most commonly reported cause among the 31 drugs with definite evidence for drug-induced thrombotic microangiopathy. In the Liles 2016 review, 92 of 101 non-dermatologic patients, 91 percent, required hospitalization, 30 needed renal replacement therapy and 3 died. A 450 mg bark capsule is not too small to trigger this. Twenty-eight of those 142 patients got their quinine from a drink.

Recommended Dosages

Dried bark, traditional bitter use: Commission E gives 1 to 3 g daily, typically divided and taken shortly before meals. At the Ph. Eur. minimum of 6.5 percent this supplies at least 65 to 195 mg of total alkaloids per day, of which roughly 20 to 117 mg is quinine-type alkaloid. That is the only cinchona dose with any official sanction anywhere.

Tincture standardized to 4 to 5 percent total alkaloids: 0.6 to 3 g daily per Commission E.

Standardized extract at 15 to 20 percent total alkaloids: 0.15 to 0.6 g daily per Commission E.

Commercial capsules: Typically 400 to 500 mg of bark powder per capsule with servings of two or three. The common 1,350 mg serving sits in the lower half of the Commission E range of 1 to 3 g, so a second serving the same day would still fall inside it, which is a measure of how loose that range is rather than a reason to take one.

Quinine sulfate as a prescription drug: 648 mg every 8 hours for 7 days for uncomplicated P. falciparum malaria in adults 16 and over. Pediatric dosing per CDC is 8.3 mg base/kg, equal to 10 mg salt/kg, three times daily for 7 days, with clindamycin 20 mg/kg/day divided three times daily for children under 8 and doxycycline 2.2 mg/kg twice daily for children 8 and over. In severe renal impairment the label directs a single 648 mg loading dose followed 12 hours later by 324 mg every 12 hours.

There is no supplement dose established for leg cramps. Any capsule marketed for that purpose is being sold for an indication FDA removed from over-the-counter availability in 1994.

Duration

Commission E sets no duration limit for bitter use, but bitters are conventionally used for days to weeks around a specific digestive complaint rather than continuously. There is no duration guidance for cinchona bark taken for cramps, because there is no dose for that use to run a clock on. The four-week figure that circulates belongs to prescription quinine prescribed and monitored by a physician; it is set out in the research section below rather than here, because it is not a supplement instruction. The hematologic risk does not decline with familiarity.

Timing & Administration

Bark preparations are taken 15 to 30 minutes before meals when the intent is appetite or digestion, because the bitter receptor response that stimulates gastric secretion depends on the compound contacting the tongue. Capsules bypass the tongue entirely, which removes the mechanism the traditional use rests on. A tincture in water is the form that matches the claim.

Quinine sulfate as a drug is taken with food to reduce gastric irritation. Time to peak is 2.8 ± 0.8 hours after a fasting 648 mg dose in healthy subjects, and about 4.0 hours when a single 324 mg capsule is taken with a high-fat breakfast, with Cmax and AUC essentially unchanged. Those are two separate studies at two different doses rather than a within-study fed and fasted comparison, so food clearly delays absorption without materially reducing it, but the size of the shift is not established. In malaria patients time to peak stretches to 5.9 ± 4.7 hours. Antacids containing aluminum or magnesium reduce and delay absorption and should be separated by several hours. Quinine is 69 to 92 percent protein bound in healthy subjects and 78 to 95 percent bound during active malarial infection, because acute-phase alpha-1-acid glycoprotein rises, so total plasma levels in illness overstate free drug.

Cinchona should not be taken for overnight cramps on any schedule, and least of all at bedtime. That schedule was invented for the quinine sulfate tablets FDA removed from over-the-counter sale, and it delivers the alkaloid at the hour when a thrombocytopenic reaction is least likely to be noticed.

Timeline of Effects

Bitter digestive effect: minutes. Gastric secretion responses to bitters occur within 10 to 30 minutes of oral contact. If a tincture is going to help appetite, the first dose tells you.

Cramp reduction in the quinine trials: two to four weeks to a measurable outcome. The Cochrane trials measured cramp number over two-week blocks, and the 28 percent reduction figure is a two-week outcome. Of the two Class I trials in the AAN review, one ran three weeks and produced 5 fewer cramps, a 37 percent mean reduction; the other took the median from 8 cramps to 6, a fall of 2 and a 25 percent median reduction. These are timelines for supervised prescription quinine, not a schedule for trying bark capsules on yourself.

Antimalarial effect: hours to days, at drug doses only. Parasite clearance with quinine at 10 mg salt/kg every 8 hours is measured in days, and the full 7-day course exists to prevent recrudescence rather than to produce symptom relief. In SEAQUAMAT the difference between artesunate and quinine showed up as mortality at 15 percent versus 22 percent, not as a slower symptom curve.

Cinchonism: 3 to 6 hours after an excessive dose. Nausea, abdominal pain, vomiting, headache, sweating, tinnitus and hearing loss appear in that window. Visual disturbance is usually delayed more than 12 hours, which is why it is frequently first noticed the following morning, and it can go on progressing for months after the exposure.

Hematologic reactions: hours, with no warning period. Patients with quinine-induced thrombotic microangiopathy characteristically recall the exact hour of onset. There is no build-up phase and no tolerance.

When to conclude it is not working. This question only arises for prescription quinine under medical supervision, because there is no cinchona dose for cramps to evaluate in the first place. Where a supervised quinine trial has run four weeks without reducing cramp frequency, it will not, and continuing past that point accumulates risk against an effect that has already failed to appear.

Benefits of Taking Cinchona

Malaria treatment, at drug doses, as a third-line agent. Quinine remains on the WHO Model List of Essential Medicines for curative treatment of falciparum malaria and in the CDC treatment tables, where it sits third for uncomplicated chloroquine-resistant disease behind artemether-lumefantrine and atovaquone-proguanil, and it is no longer first line for severe disease. SEAQUAMAT (The Lancet, 2005) randomized 1,461 patients with severe falciparum malaria, 730 to artesunate and 731 to quinine, and found mortality of 15 percent against 22 percent, a 34.7 percent relative reduction (95 percent CI 18.5 to 47.6, p = 0.0002). AQUAMAT (The Lancet, 2010) randomized 5,425 African children across 11 centers in 9 countries and found 230 of 2,712 deaths on artesunate against 297 of 2,713 on quinine, 8.5 percent against 10.9 percent, odds ratio 0.75 (95 percent CI 0.63 to 0.90), relative reduction 22.5 percent (95 percent CI 8.1 to 36.9, p = 0.0022). Post-treatment hypoglycemia was also less frequent on artesunate, 48 of 2,712 at 1.8 percent against 75 of 2,713 at 2.8 percent, odds ratio 0.63 (0.43 to 0.91, p = 0.0134).

Cramp frequency reduction, modest and real. Both Cochrane and the AAN found quinine modestly effective and then declined to recommend routine use. That is a judgment that a small benefit does not justify a rare, unpredictable and sometimes fatal harm, and it is a judgment about supervised prescription quinine, which is better characterized and better monitored than anything in a bark capsule.

Appetite and dyspepsia, on traditional-use grounds. Commission E approval reflects long use and a plausible bitter mechanism, not controlled trials. No dose-response study exists.

What is not a benefit. Cinchona does not treat or prevent COVID-19, influenza or any other viral illness. Quinine's structural similarity to hydroxychloroquine has been used in marketing since 2020 and there is no human trial evidence supporting cinchona for any viral infection.

Potential Negatives & Side Effects

Cinchonism, the expected dose-dependent syndrome. The Qualaquin label states plainly that cinchonism occurs to some degree in almost all patients taking quinine at therapeutic doses. Mild form: headache, vasodilation and sweating, nausea, tinnitus, hearing impairment, vertigo or dizziness, blurred vision and disturbance in color perception. Severe form: vomiting, diarrhea, abdominal pain, deafness, blindness and disturbances in cardiac rhythm or conduction.

Hearing loss. Quinine produces reversible high-tone hearing loss that tracks plasma concentration, documented in healthy volunteers in the British Journal of Clinical Pharmacology literature. It resolves as the drug clears in nearly all therapeutic-dose cases.

Immune thrombocytopenia. Quinine is the archetype. In the Medicare claims analysis cited by Hogan in CMAJ 2015, quinine users showed immune thrombocytopenic purpura at 1.67 per 1,000 person-years and thrombotic microangiopathy at 0.23 per 1,000 person-years, with incidence rate ratios against diltiazem of 4.2 (95 percent CI 2.5 to 6.5) and 6.9 (95 percent CI 1.3 to 24.0).

Hemolytic uremic syndrome and thrombotic thrombocytopenic purpura. These carry the Qualaquin boxed warning and are the reason FDA imposed a Risk Evaluation and Mitigation Strategy with a Medication Guide and a Dear Health Care Provider letter on July 8, 2010.

Cardiac conduction. In a 26-subject crossover study in the Qualaquin label, 13 young and 13 elderly subjects dosed for 7 days at 648 mg three times daily, the maximum mean QTcI difference from placebo after baseline correction was 27.7 msec, with a 95 percent upper confidence bound of 32.2 msec. The same study found the PR interval prolonged by a maximum mean 14.5 msec and QRS by 11.5 msec. Quinidine, present in bark alongside quinine, has stronger Class Ia sodium channel activity.

Hypoglycemia. Insulin release is stimulated directly, most dangerously in acute malaria, in pregnancy and in anyone fasting.

Gastrointestinal upset. In the Cochrane pooled data, minor adverse events were more common with quinine than placebo, mostly gastrointestinal, with a risk difference of about 3 percent, 95 percent CI 0 to 6 percent. One participant in those trials developed thrombocytopenia on quinine, a 0.12 percent risk.

Other documented reactions. Liles 2016 cataloged chills, fever, hypotension, painful acral cyanosis, disseminated intravascular coagulation, hemolytic anemia, neutropenia, acute kidney injury, rhabdomyolysis, liver toxicity, cardiac ischemia, respiratory failure, blindness and toxic epidermal necrolysis among the 142 reviewed patients.

Deficiency Symptoms

There is no such thing as cinchona deficiency, and no such thing as quinine deficiency. Humans do not synthesize, store, require or regulate any cinchona alkaloid. No enzyme uses one as a cofactor, no transporter exists for one, and no clinical sign has ever been attributed to a lack of one. Contrast iron or iodine, where withdrawal produces a predictable, measurable, reversible syndrome on a known timeline.

What cinchona addresses

• Symptomatic muscle cramping, through quinine's action on the motor end plate, at drug doses.

• Blood-stage malaria infection, through quinine's interference with parasite heme detoxification, at drug doses.

• Subjective appetite and postprandial fullness, through bitter receptor stimulation, at bitter doses.

None of these is a deficiency state. Each is a symptom or an infection being acted on by a plant alkaloid with drug-like behavior.

Bottom line

If a product page implies you are low in something cinchona supplies, that claim has no biochemical referent. Blood tests for quinine exist only as toxicology assays, run to find out how much of an unwanted exposure someone has, never to find out whether someone needs more.

Toxicity Symptoms

At high intake

Quinine toxicity is one of the better characterized dose-response relationships in clinical toxicology.

• Above roughly 1 g of ingested quinine, some degree of cinchonism usually appears: nausea, vomiting, tinnitus, headache.

• Above roughly 5 g, cardiotoxicity, central nervous system disturbance and blindness become common.

• Above roughly 10 g, those effects are close to universal.

• Plasma quinine concentrations above 10 mg/L are associated with visual impairment. Concentrations above 15 mg/L are associated with cardiac arrhythmias.

• In children under 6 years old, as little as 600 mg, two adult tablets, can cause life-threatening toxicity.

Ocular damage is a direct toxic effect on the inner retina. Optical coherence tomography shows acute inner retinal thickening with hyperreflectivity, progressing to inner retinal atrophy and optic nerve pallor over the months that follow, and residual visual field constriction is a common permanent outcome.

Reaching 1 g of quinine from bark at the Murauer and Ganzera concentrations would take 53 to 63 g of bark, roughly 118 to 140 capsules of a 450 mg product. Acute quinine overdose from cinchona capsules is therefore not the realistic hazard, which is not the same thing as saying the capsules are safe. The antibody-mediated reaction, which needs no threshold and can follow a single capsule, is the hazard.

Signs to reduce or stop

• Ringing in the ears, muffled hearing or any new hearing change.

• Blurred vision, loss of color discrimination, tunnel vision or any visual change at all. Stop immediately and seek care; visual toxicity is usually delayed more than 12 hours and can be permanent.

• Unexplained bruising, petechiae, nosebleeds, bleeding gums, blood in urine or stool.

• Dark urine, reduced urine output, or sudden pallor with fatigue, which can signal hemolysis or acute kidney injury.

• Palpitations, presyncope or syncope.

• Any rash, mucosal blistering or skin peeling.

General note

Multiple-dose activated charcoal is indicated after ingestions above 5 g or with any visual disturbance. Sodium bicarbonate is used for QRS widening beyond 100 msec, and magnesium sulfate 10 mmol intravenously over 15 minutes for torsades de pointes. These are hospital interventions. A person with visual symptoms after cinchona should be in an emergency department, not waiting to see whether it clears.

How Cinchona Works

Against the malaria parasite. Plasmodium digests hemoglobin inside an acidic food vacuole, releasing free heme that is toxic to the parasite. The parasite neutralizes it by crystallizing it into hemozoin. Quinine and the other quinoline antimalarials concentrate in that vacuole and interfere with hematin crystallization, leaving free heme to accumulate and catalyze peroxidative damage and inhibit parasite cysteine proteases. The result is death of the blood-stage parasite. This mechanism requires micromolar concentrations at the parasite, which requires the 648 mg three-times-daily regimen, which is why bark does not do it.

Against muscle cramp. Quinine decreases the excitability of the motor end plate and increases the muscle refractory period, as described by Hogan in CMAJ 2015. It reduces the response of the end plate to acetylcholine and to repetitive nerve stimulation. This is also why it is contraindicated in myasthenia gravis, where end plate safety margin is already lost, and why it can worsen neuromuscular blockade.

As a bitter. Quinine is the standard agonist used in taste research for the TAS2R family of bitter receptors. Oral bitter receptor activation increases salivary and gastric secretion and is the basis of the entire bitter tonic tradition. This effect is purely local to the mouth and upper gut and requires no systemic absorption.

Why the reactions happen. Quinine-dependent antibodies bind platelet glycoproteins, chiefly GPIb/IX and GPIIb/IIIa, only in the presence of quinine. The antibody is already there in a sensitized person, so the reaction is immediate and independent of how much quinine arrives. In vitro work by Perdomo and colleagues (Blood, 2011, volume 117, issue 22, pages 5975 to 5986) has shown quinine-dependent GPIb/IX antibodies also inhibit megakaryocyte and proplatelet production, which helps explain why recovery can lag removal of the drug.

Pharmacokinetics. Quinine is metabolized mainly by CYP3A4 to 3-hydroxyquinine, which is less active than the parent. Half-life is 9.7 to 12.5 hours in healthy adults.

Synergistic Supplements

Synergy applies poorly here, because cinchona's useful effects come from a drug-like alkaloid and the sensible pairings are the ones that reduce need or reduce risk.

• Magnesium. Frequently paired with cinchona in cramp products. Magnesium has its own modest and contested cramp evidence and none of quinine's hematologic risk. If a cramp product contains both, the magnesium is doing the safe part of the work. Note that magnesium delays and reduces quinine absorption, so the pairing is not pharmacokinetically inert.

• Gentian root (Gentiana lutea) and wormwood (Artemisia absinthium). Traditional bitters that activate the same TAS2R receptors. For appetite and dyspepsia these do the job without quinine alkaloids.

• Vitamin B complex. The AAN review rated vitamin B complex, naftidrofuryl and calcium channel blockers such as diltiazem as possibly effective for cramps at Level C, and named them as the agents to consider before quinine.

• Doxycycline, tetracycline or clindamycin. Genuinely synergistic with quinine, but only in malaria treatment and only by prescription, added to shorten courses and prevent recrudescence.

• What to avoid stacking. Any other botanical with QT effects, any other bitter alkaloid source, and anything that inhibits or induces CYP3A4.

Interactions & What NOT to Take

Every interaction below is documented with quinine specifically, with the magnitude where the Qualaquin label or a trial provides one.

• Rifampin. The most dramatic. Pukrittayakamee and colleagues (Antimicrobial Agents and Chemotherapy, 2003, volume 47, issue 5, pages 1509 to 1513) randomized 59 adults with falciparum malaria to quinine 10 mg salt/kg three times daily alone (n = 30) or with rifampin 15 mg/kg/day for 7 days (n = 29). Median quinine AUC fell from 47.5 to 11.7 mcg/mL per day, roughly 76 percent. Recrudescence rose from 3 of 25 (12 percent) to 15 of 23 (65 percent). The label reports a 75 percent AUC reduction in malaria patients and up to 85 percent in healthy subjects.

• Carbamazepine. Quinine raises carbamazepine AUC by 104 percent and Cmax by 56 percent.

• Phenobarbital. Quinine raises phenobarbital AUC by 81 percent and Cmax by 53 percent.

• Digoxin. Quinine raises steady-state digoxin AUC by 33 percent and cuts steady-state biliary clearance by 35 percent.

• Ketoconazole. Raises quinine AUC by 45 percent and lowers quinine oral clearance by 31 percent. Expect the same direction from itraconazole.

• Ritonavir. Not an extrapolation and an order of magnitude beyond ketoconazole: the label reports 4-fold increases in mean quinine AUC and Cmax, and directs that the combination be avoided.

• Erythromycin and troleandomycin. CYP3A4 inhibition raising quinine exposure.

• Phenytoin. Induction lowering quinine exposure, same mechanism as rifampin and phenobarbital.

• Warfarin. Quinine can enhance the anticoagulant effect. The combination of an INR shift and a drug that can crash the platelet count is a bad pairing on two independent grounds.

• Mefloquine and halofantrine. Additive cardiac conduction and seizure risk. Mefloquine also cross-reacts for hypersensitivity.

• Neuromuscular blocking agents. Quinine potentiates them, including succinylcholine and the non-depolarizing agents.

• Theophylline. Altered clearance.

• Metoprolol, flecainide and other CYP2D6 substrates. Quinine inhibits CYP2D6 at antimalarial concentrations. Note that Donovan 2003 showed 80 mg of quinine from tonic water did not produce this effect, so the concern scales with dose.

• Antacids containing aluminum or magnesium. Reduce and delay quinine absorption, which is also a reason not to take a magnesium product at the same time as anything carrying quinine.

• Other QT-prolonging drugs. Amiodarone, sotalol, dofetilide, haloperidol, citalopram, ondansetron and macrolides, all additive with quinine and quinidine.

Quality, Testing & Adulteration

Identity is the first problem. Cinchona officinalis L. is the most commonly printed name on labels and the least commercially important. C. pubescens Vahl, C. calisaya Wedd. and C. ledgeriana are what plantations actually grow, and their alkaloid profiles differ substantially, with C. ledgeriana Java bark reaching 8 to 13 percent quinine against roughly 1.6 to 1.9 percent in generic pharmacy bark.

Substitution with unrelated bitter barks is documented. Remijia species, close Rubiaceae relatives that also make cinchona alkaloids, have long been traded as cinchona, historically as cuprea bark. In Brazil a range of unrelated bitter plants are traded under the name "quina," documented in the Journal of Ethnopharmacology. Bitterness is not species identification, and a powdered bark that tastes correct tells a buyer nothing.

What a certificate of analysis should show for cinchona, specifically. Botanical species with author citation, plant part, and a macroscopic or DNA-based identity test. Quantified quinine, quinidine, cinchonine and cinchonidine by HPLC or supercritical fluid chromatography, each reported individually in percent of dry weight, not as an undifferentiated "total alkaloids" number. Total alkaloids alone is insufficient, because cinchonine and cinchonidine together often exceed quinine, as they did in all four samples Murauer and Ganzera analyzed. Heavy metals, microbial limits, pesticide residues, loss on drying, and country of origin.

What the market actually provides. Almost none of that. Bark capsule labels commonly state milligrams of bark and nothing else. No mainstream cinchona supplement carries USP Verified or NSF Certified for Sport marks, ConsumerLab has not published a cinchona category review, and there is no USP-NF monograph for cinchona bark as a dietary ingredient, though quinine sulfate has a long-standing drug monograph.

What a buyer can verify. Three things, all by email before purchase. Ask for the Latin binomial with authority and the plant part. Ask for a chromatogram showing individual alkaloid percentages with the method named. Ask that the lot number on that certificate match the lot in the bottle. A seller who cannot supply a per-alkaloid assay is selling an ingredient whose only pharmacologically active component is unmeasured.

Special Considerations

Pregnancy. Commission E contraindicates cinchona bark in pregnancy. Qualaquin is Pregnancy Category C, with the label noting animal data suggesting potential fetal harm while citing a Thai study that found stillbirth rates of 1.6 percent with quinine against 1.8 percent in controls, and spontaneous abortion at 3.5 percent with quinine against 10.9 percent in controls. Those numbers reflect treated malaria, itself dangerous in pregnancy, and do not support supplemental cinchona use. Quinine-induced hypoglycemia is more pronounced in pregnancy.

Breastfeeding. Estimated infant exposure through milk is under 2 to 3 mg per day, less than 0.4 percent of the maternal dose. Quinine is generally considered compatible with breastfeeding at therapeutic doses, but a G6PD-deficient infant is a separate consideration.

Children. Commission E does not recommend cinchona bark under age 12, and 600 mg of quinine in a child under 6 can be life-threatening.

G6PD deficiency. Absolute contraindication on the Qualaquin label, affecting roughly 400 million people worldwide, concentrated in populations with historical malaria exposure, which is the same population most likely to encounter cinchona in traditional medicine.

Surgery. Discontinue at least two weeks before elective surgery. Quinine potentiates neuromuscular blockers, can affect platelet counts and can prolong the QT interval, all of which matter in an operating room.

Homeopathy. Samuel Hahnemann's 1790 self-experiment with cinchona bark, while translating William Cullen's materia medica, is the founding anecdote of homeopathy. Preparations labeled China officinalis are diluted past the point where cinchona alkaloids remain measurable, sit in a separate regulatory category from bark supplements, and are not the subject of anything in this issue.

People who drink tonic water regularly. This is the population most likely to be quietly sensitized. Twenty percent of the 142 patients in the Liles 2016 review reacted to beverage exposure. Anyone who has had unexplained bruising, a low platelet count or an episode of acute kidney injury after an evening of gin and tonic should mention that timing to a hematologist, and should not then add a cinchona capsule.

Research Status & Evidence Quality

Tier 1, strong evidence from large randomized trials. Quinine's antimalarial efficacy and its inferiority to artesunate for severe malaria. SEAQUAMAT (n = 1,461, 2005) and AQUAMAT (n = 5,425, 2010) are large, multicenter and unambiguous. This tier concerns quinine the drug, at drug doses.

Tier 2, moderate evidence from pooled randomized trials. Quinine's effect on muscle cramps. Twenty placebo-controlled trials and 1,140 participants give a 10 percent reduction in cramp intensity on moderate quality evidence, with the 28 percent cramp-number and 20 percent cramp-day reductions rated low quality. Fifty-eight percent of the participants in the review came from five unpublished studies. The AAN's Level A rating rests on two Class I studies. The effect exists and is small.

Hogan (CMAJ, 2015, volume 187, issue 4, pages 237 to 238) allows that a four-week trial of prescription quinine could be an option for a fully informed patient with frequent severe cramps that disrupt sleep, but only after treatable causes have been ruled out and non-drug measures have failed. His article is titled to argue that quinine is not a safe drug for this use, and nothing in that reasoning transfers to an unassayed bark capsule. Trial exposure in the Cochrane review ran up to 60 days.

Tier 3, observational and pharmacovigilance evidence on harm. 665 FDA adverse event reports with serious outcomes and 93 deaths from 1969 through September 11, 2006. Thirty-eight US cases and 2 deaths in FDA's April 2005 to October 2008 review. Seventy-one serious adverse reactions to Health Canada as of September 30, 2010, of which 41 were life-threatening or required hospitalization. Medicare incidence rates of 1.67 and 0.23 per 1,000 person-years for immune thrombocytopenic purpura and thrombotic microangiopathy. One hundred forty-two systematically reviewed case reports.

Tier 4, traditional use only. Cinchona bark for appetite and dyspepsia, on Commission E approval with no controlled trial.

Tier 5, no human evidence. Cinchona bark, as distinct from quinine, for anything. There is no randomized controlled trial of standardized cinchona bark extract for cramps, for digestion, for immune function or for any other indication. Every efficacy number in this issue comes from isolated quinine.

Research Limitations

• The borrowed-research problem is total here. Not one clinical trial has been run on cinchona bark as a supplement. Everything sellers cite was run on quinine sulfate at 200 to 648 mg per dose.

• Bark alkaloid content is rarely measured. The best available published quantification of pharmacy-grade bark is four samples in one 2018 paper.

• The cramp trials could not see the outcome that matters. Cochrane found no significant difference in major adverse events, risk difference 0 percent, across 1,140 participants in the placebo comparison with exposure running up to 60 days. One of those participants did develop thrombocytopenia on quinine, a 0.12 percent risk. A reaction rate near 1.67 per 1,000 person-years cannot be reliably estimated at that sample size, so the absence of a statistical signal is a sample size artifact rather than evidence of safety.

• Adverse event reporting is passive. FAERS and Health Canada counts are spontaneous reports, and the true denominator of cinchona and tonic water exposure is unknown.

• No pharmacokinetic study of bark exists. Nobody has measured plasma quinine after a 1,350 mg bark serving, so the absorbed dose from a supplement is a calculation rather than a measurement.

• Species identity in published work is inconsistent. Papers often say "Cinchona bark" with no binomial, which makes cross-study comparison of alkaloid content unreliable.

Summary & Key Takeaways

Bottom Line

Cinchona bark is the natural source of a drug that United States regulators spent thirteen years removing from self-medication, and the only approved quinine products left, quinine sulfate 324 mg capsules, carry a boxed warning against exactly the use that bark capsules are sold for. If you want the antimalarial effect, you need a prescription and 1,944 mg of quinine sulfate a day, which no capsule supplies. If you want a bitter for appetite, gentian root does the same job without quinoline alkaloids. If you want cramp relief, cinchona is not the answer: the 28 percent fewer cramps over two weeks on low quality evidence was measured with prescription quinine, and the American Academy of Neurology, FDA and Health Canada all concluded even that is not worth the hematologic risk.

Key Safety Points

• Quinine-induced immune thrombocytopenia and hemolytic uremic syndrome are antibody-mediated and not dose-dependent. A small exposure in a sensitized person is enough, and quinine is the most commonly reported cause of drug-induced thrombotic microangiopathy, with 44 definite cases in the Oklahoma registry against 31 drugs with definite evidence.

• Absolute contraindications: prolonged QT interval, G6PD deficiency, prior quinine hypersensitivity, mefloquine or quinidine hypersensitivity, myasthenia gravis, optic neuritis, and pregnancy for bark preparations.

• Stop and seek care immediately for any visual change, unexplained bruising or bleeding, dark urine, or new tinnitus. Visual toxicity is usually delayed more than 12 hours, can go on progressing for months afterward, and can be permanent.

• Rifampin cuts quinine exposure by about 75 percent and raised treatment failure from 12 percent to 65 percent in a 59-patient trial. Do not combine.

• Do not stack a cinchona capsule on top of a regular tonic water or quinquina aperitif habit. Both are quinine exposures and neither is measured.

Special Note

The number worth carrying out of this issue is 28 out of 142. That is the share of systematically reviewed quinine reaction patients whose exposure came from a beverage rather than a pill, from tonic water, Schweppes Bitter Lemon or Dubonnet, at roughly 13 to 23 mg of quinine per serving under a federal cap of 83 parts per million with mandatory disclosure on the label. A 1,350 mg serving of cinchona bark capsules delivers a comparable or larger amount of the same alkaloid, with no cap, no disclosure and no assay. The regulation that governs a mixer is stricter than the regulation that governs the capsule sold to treat a medical complaint, and that asymmetry is the whole story of this ingredient.