Hydrangea Root

What is Hydrangea Root?

Hydrangea root is the dried root of Hydrangea arborescens, an eastern North American shrub whose roots held 0.41% coumarins (as umbelliferone) in a 2023 assay. That figure comes from Murzabulatova and colleagues in Biology Bulletin of the Russian Academy of Sciences (volume 50, pages 362 to 370), who compared leaf, stem and root of the same plants, grown at a botanical garden in the southern Urals, and found the coumarin fraction highest in the root. It is the most specific modern chemistry number published for the part of the plant that goes into capsules.

The species is not obscure. 'Annabelle', the white-flowered garden hydrangea that plant geneticists now study for its flower scent and color, is a cultivar of H. arborescens. The 1918 Dispensatory of the United States, edited by Joseph Remington and Horatio Wood, carried a hydrangea monograph under an N.F. IV heading, reported that a decoction had been used "with great advantage among the Cherokee Indians, and subsequently by settlers, in calculous diseases," and gave a dose of thirty grains (1.9 g). King's American Dispensatory (1898) credits Dr. S. W. Butler of Burlington, New Jersey, with introducing it to physicians as a remedy for bladder gravel.

Chemists tried to find the active principle early. C. S. Bondurant reported a crystalline glucoside, hydrangin, in the American Journal of Pharmacy in March 1887; Schroeter obtained a yield of 0.08% of it in 1889. Neither found anything that has since been tied to a measured effect in people.

Today the root is sold in the United States as capsules (Nature's Way lists 370 mg per capsule) and as alcohol extracts (Herb Pharm describes its roots as "sustainably wildcrafted"), usually marketed for urinary, kidney or prostate support. The Natural Medicines database, as reproduced by RxList, rates the evidence as insufficient for kidney stones, enlarged prostate, prostate and bladder infections and hay fever.

Common Names

Seven barks (the name Bondurant used in 1887), wild hydrangea, smooth hydrangea, hills of snow, hortensia, and simply hydrangea. The ASPCA plant database lists Hortensia, Hills of Snow and Seven Bark as alternate names for H. arborescens.

Primary Active Compounds

• Coumarins: 0.41% ± 0.007% of the root, expressed as umbelliferone (7-hydroxycoumarin), in the 2023 Russian analysis. The ChEBI chemical database lists "hydrangin" as a synonym for umbelliferone.

• "Hydrangin": Bondurant's 1887 glucoside, which gave an opal-blue fluorescence in alkaline solution, melted at 235 °C and split into glucose and a resin-like body on acid hydrolysis. Schroeter reported a 228 °C melting point and a 0.08% yield.

• Other root constituents from 19th century analyses: saponin, several resins, sugar, fixed and volatile oils (2.28%) and starch (7.28%). King's records that, contrary to an 1881 report, "no tannin was found."

• Leaf constituents (not the root): tannins 7.13%, flavonoids 1.14% and ascorbic acid 0.28% in the 2023 analysis.

• Cyanogenic glycosides: the ASPCA names "cyanogenic glycoside" as the toxic principle of H. arborescens. This issue's research found no published measurement of cyanogenic glycoside content in H. arborescens root. The cyanogenic glycosides that have been quantified (taxiphyllin) come from the leaves of a different species, H. macrophylla.

Key Note

At least four different plants travel under the hydrangea name in research and commerce: H. arborescens root (American supplements), H. paniculata stems (Chinese kidney research), H. serrata and H. macrophylla leaves (Korean and Japanese skin, weight and sweet-tea products), and, since a 2015 reclassification by De Smet and Granados in the journal Taxon (volume 64, page 750), the Chinese antimalarial herb chang shan, formerly Dichroa febrifuga and now also named Hydrangea febrifuga. A study on one says nothing reliable about the others. Read the Latin binomial and the plant part on every label and every citation.

Everything below concerns H. arborescens root unless another species is named.

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Primary Functions & Benefits

Hydrangea root is sold for three jobs: easing urinary "gravel" and stones, supporting the prostate, and a loosely defined kidney "tonic" effect. None of the three has been tested in a published human trial of H. arborescens.

The original claim, in the original words

King's American Dispensatory (1898) describes Butler's use as "relieving the excruciating pain attendant on the passing of a calculus through the ureter," and says the herb works "by its own specific action on the bladder" to remove deposits already there. King's also reports, and Maud Grieve's A Modern Herbal (1931) repeats, that "as many as 120 calculi have been known to come from one person under the use of this remedy." That is a single anecdote with no denominator, no imaging and no comparison group. Felter's 1922 entry lists the specific indications as "vesical and urethral irritation, with gravel; difficult urination; deep-seated renal pain; bloody urine," and says the herb was "believed to be of value in preventing their formation," particularly "alkaline and phosphatic concretions."

What the 1880s marketing added

In July 1885 the Buffalo Medical and Surgical Journal reprinted a Philadelphia note that Lambert & Co. of St. Louis had combined hydrangea with lithia in a product called "Lithiated Hydrangea." It cited two cases of "rheumatic gout with renal complications" reported by Dr. F. S. Senier of Waukesha, Wisconsin, treated with a drachm three times daily. Two uncontrolled cases of a combination product are the only 19th century journal case reports this issue found beyond the Eclectic textbooks.

What modern laboratories have actually tested

The renal studies cited for hydrangea root come from one group at the Institute of Materia Medica in Beijing, and it uses H. paniculata, a Chinese species, not H. arborescens:

• Zhang and colleagues (Frontiers in Pharmacology, 2017) gave mice an oral water or ethanol extract of H. paniculata three times before an injection of bacterial lipopolysaccharide. Blood urea nitrogen and plasma NGAL fell and survival improved.

• A 2017 study in Evidence-Based Complementary and Alternative Medicine gave mice the same coumarin-rich extract orally five times around a single 20 mg/kg cisplatin injection, and reported lower urea and creatinine.

• Skimmin, an umbelliferone glucoside from H. paniculata, at 15 and 30 mg/kg reduced albumin excretion in a rat model of membranous glomerulonephritis (2013) and, at 7.5 to 30 mg/kg for 17 weeks, slowed streptozotocin diabetic kidney damage in rats (European Journal of Pharmacology, 2012).

• Total H. paniculata coumarins at 7.5, 15 and 30 mg/kg for nine weeks improved kidney function in a rat membranous nephropathy model (Phytomedicine, 2021).

All of these are drug-induced or immune kidney injury models. None is a stone model, none measured crystal formation, and none used the root of the American species.

The only randomized human trials of any hydrangea

Both used a hot-water leaf extract of Hydrangea serrata from Korea. Myung and colleagues (Nutrients, 2020) randomized 151 adults to 300 mg, 600 mg or placebo daily for 12 weeks and reported improvements in wrinkle and hydration measures and in some elasticity measures, mostly at 600 mg, with no change in water loss through the skin; the authors name hydrangenol as the extract's active component. Han and colleagues (Nutrients, 2022) gave 600 mg daily or placebo for 12 weeks to 93 overweight or obese adults and reported lower body weight and fat mass. Both trials included co-authors from COSMAXBIO, a Korean ingredient company, and neither species nor plant part matches a hydrangea root bottle.

Folk and veterinary use

A 2019 review in the Journal of Ethnopharmacology, built on 2003 interviews with 60 organic farmers and holistic practitioners in British Columbia, recorded H. arborescens among plants used for joint pain and arthritis in pets. That documents a practice; it does not test one.

The diuretic idea

Natural Medicines suggests the constituents "may cause increased urine output." This issue's research found no study that measured urine volume after H. arborescens in animals or people. Urinary "flushing" as a general herbal claim belongs to the Goldenrod issue.

Forms & Standardization

No hydrangea root product located for this issue is standardized to any marker compound. Labels state milligrams of root or of extract, and nothing else.

Dried root capsules

Nature's Way "Root Hydrangea" lists 740 mg of Hydrangea arborescens root per two-capsule serving (370 mg per capsule), 50 servings per bottle, gelatin and magnesium stearate as the only other ingredients, and the direction "Take 2 capsules two times daily, preferably with food." That label adds up to 1,480 mg of root per day, in two 740 mg doses. Other capsule lines on the US market include Swanson (500 mg), Piping Rock (1,000 mg per serving) and Nature's Sunshine.

Liquid extracts

Herb Pharm's Hydrangea extract is made from H. arborescens root in certified organic cane alcohol and distilled water at a 1:3 dry herb to menstruum ratio. Its label listing gives a 0.7 mL serving (one dropper squeeze), stated as 630 mg of extract, taken in 2 oz of water 2 to 4 times daily, best between meals. At 1:3, 0.7 mL corresponds to roughly 0.23 g of dried root by our arithmetic, or about 0.9 g at four servings. A medicinal plant monograph published by Southern Cross University in Australia lists a weaker 1:5 tincture in 40% alcohol.

Teas and decoctions

There is no standard tea. One widely read consumer site suggests simmering "1 tablespoon (15 grams)" in a cup of water. Fifteen grams is more than seven times the 2 g single amount that Natural Medicines rates as likely unsafe (see Potential Negatives below). The Southern Cross University monograph also lists 6 to 12 g of dried root a day; split three ways, the upper end is 4 g per dose, twice that line.

What the marker would be, if anyone used one

The only quantified marker in the root is total coumarins, 0.41% as umbelliferone. If a capsule's root matched the 2023 sample, a 370 mg capsule would carry about 1.5 mg of coumarins and the Nature's Way daily direction about 6 mg. Root from different stands, harvest seasons and drying conditions has not been compared, so treat that as an order of magnitude, not a specification.

Historical preparations (history, not dosing guidance)

• Felter (1922): root, 5 to 60 grains (about 0.3 to 3.9 g); Specific Medicine Hydrangea, 5 to 60 drops.

• King's (1898): "specific hydrangea," 5 to 30 drops three times a day in hot water; a concentrated syrup made with sugar or honey, a teaspoonful three times daily.

• Dispensatory of the United States (1918): thirty grains (1.9 g).

• Grieve (1931): fluid extract, 30 to 100 minims.

• Lithiated Hydrangea (Lambert & Co., St. Louis): hydrangea plus lithia, which King's dosed at 1 to 2 fluid drachms four times daily.

Other species' extracts, which are not substitutes

• H. paniculata total coumarins: a water extract of the stem rich in coumarin glycosides, chiefly skimmin. A 2018 Phytomedicine paper described it as under preclinical development in China as a "class 5" herbal drug for membranous nephropathy. In rodents its coumarins are metabolized to umbelliferone and esculetin.

• H. serrata hot-water leaf extract: 300 to 600 mg daily in the two Korean trials above.

• H. macrophylla var. thunbergii leaf: dried and fermented in Japan as the crude drug "Sweet Hydrangea Leaf" (amacha), sweet from phyllodulcin.

Food Sources

Hydrangea is not a food, and no part of the genus contributes anything nutritionally. The relevant question is how people end up swallowing it.

Routes of exposure

• Supplements: capsules and alcohol extracts of H. arborescens root, as above.

• Garnish: in June 2008, Japan recorded two outbreaks after diners ate hydrangea leaves served as decoration (details under Toxicity Symptoms). Japan's Ministry of Health, Labour and Welfare advises that hydrangea, sometimes placed under sashimi, should not be eaten.

• Sweet tea: decoctions of Sweet Hydrangea Leaf (H. macrophylla var. thunbergii) have been followed by vomiting, according to a 2023 Journal of Natural Medicines paper from Kyoto Pharmaceutical University.

• Skin contact: gardeners, florists and nursery workers handle the living plant (see Potential Negatives).

Umbelliferone itself occurs in common foods such as carrot and coriander, but no study has compared dietary umbelliferone intake with the amount in a hydrangea capsule, so there is no "eat the food instead" calculation to make.

Who Should Take Hydrangea Root

No group of people has trial evidence of benefit from H. arborescens root, so this section is about who is buying it and what they should know first.

The two typical buyers

• Someone with kidney stones or "gravel." The 1922 Eclectic claim was prevention of "alkaline and phosphatic concretions," not dissolution, and it was never tested. Stone prevention depends on what the stone is made of, which only a lab analysis of a passed or retrieved stone can tell you. Calcium oxalate, uric acid, struvite and cystine stones are prevented in different ways, and no hydrangea label tells you which type it is supposed to address.

• A man with prostate or bladder symptoms. Natural Medicines rates hydrangea's evidence for enlarged prostate and for prostate and bladder infections as insufficient. Infection needs a diagnosis and usually an antibiotic; prostate enlargement has approved drugs with large trial records.

If an adult still wants to try it

The lowest-risk version of the decision looks like this: an adult with no kidney disease, not pregnant or breastfeeding, not taking lithium, with no history of hydrangea skin allergy, whose urinary symptoms have already been evaluated, staying within a label's directions and stopping within the short window the labels themselves set. That describes tolerability, not expected benefit.

Who should get tested instead

Anyone passing visible grit or stones should save it for analysis, and anyone with blood in the urine, flank pain or fever should be examined. An herb taken in place of that workup costs time the kidney may not have.

Who Should AVOID or Use Caution

Contraindications

• Lithium therapy. Natural Medicines rates the hydrangea and lithium interaction as moderate, on the reasoning that a diuretic effect could reduce lithium clearance and raise blood levels.

• Pregnancy and breastfeeding. There are no safety data in either setting.

• Known hydrangea allergy. A positive patch test to hydrangea leaf, stem or the allergen hydrangenol, or a history of hand eczema from handling the plant.

• Suspected obstruction. Severe flank pain with fever, vomiting, or inability to pass urine is an emergency, not a supplement question.

• Children. No pediatric safety data exist. A third-party listing of Herb Pharm's extract, drawing on label-database records, gives the target group as adults and children 4 or more years of age, while a retailer's transcription of the same label shows no age statement; nothing in the published literature supports pediatric use.

Use Caution

• Prescription diuretics (furosemide, hydrochlorothiazide), where any added fluid loss is unpredictable.

• Chronic kidney disease. The rodent kidney-protection data come from a different species and do not establish safety in damaged human kidneys.

• Gardeners and florists with hand eczema, who may already be sensitized to the living plant.

• Pet owners. The ASPCA lists H. arborescens as toxic to dogs, cats and horses; store capsules and dried root out of reach.

Critical Safety Point

The same warning appears in sources more than a century apart. King's (1898): overdoses "produce some unpleasant symptoms, as dizziness of the head, oppression of the chest, etc." The Dispensatory of the United States (1918): "vertigo, oppression of the chest." Natural Medicines today rates more than 2 g of dried root at a time as likely unsafe and long-term use as likely unsafe. That 2 g line sits almost exactly on the 1918 standard dose of thirty grains (1.9 g), so the historical "normal" amount and the modern caution threshold are effectively the same number. With no demonstrated benefit to weigh against it, there is no reason to approach it.

Recommended Dosages

There is no evidence-based dose of hydrangea root, because no human trial has tested one. The figures below are what labels and a safety database state, reported as facts about those documents, not as amounts to take.

Capsules (label directions)

Nature's Way: 2 capsules (740 mg of root) two times daily, 1,480 mg per day, with the warnings "Do not exceed recommended dose" and "Not recommended for long-term use."

Liquid extract (label directions)

Herb Pharm (1:3): 0.7 mL in 2 oz of water, 2 to 4 times daily, roughly 0.23 g of root per serving by arithmetic.

Tea or decoction

No defined amount exists. A 15 g tablespoon, as one consumer site suggests, is far beyond the safety line below.

Safety ceiling (Natural Medicines)

More than 2 g of dried root or rhizome at one time: "likely unsafe." Short-term use for "only a few days": "possibly safe."

Duration

Every source that addresses duration points the same way: the Nature's Way label says not for long-term use, and Natural Medicines rates long-term use as likely unsafe. No source defines "long-term" in days or weeks.

Timing & Administration

• With or without food: the labels disagree. Nature's Way says "preferably with food"; Herb Pharm says "best taken between meals." No study has compared the two. Taking it with food is the conservative choice for anyone who gets nausea.

• Liquid extracts: dilute in at least 2 oz of water or juice, as the Herb Pharm label directs; the base is alcohol.

• Single doses: both labels reviewed here stay well under the 2 g single-dose line; homemade teas often do not.

• Lithium: not a timing problem. Spacing doses apart does not address a clearance interaction.

• Storage: dogs and cats chew bottles. Keep it where they cannot reach it.

Timeline of Effects

No human study of H. arborescens exists, so there is no measured onset, peak or plateau for any outcome.

What comparable studies used

• The H. serrata leaf extract trials ran 12 weeks, with measurements at 4, 8 and 12 weeks; wrinkle differences versus placebo appeared at 8 and 12 weeks (Myung, 2020).

• The H. paniculata rodent kidney studies ran from a few days (acute injury) to nine weeks (membranous nephropathy) and 17 weeks (diabetic nephropathy).

Neither timeline transfers to a different species, plant part and condition.

For stones, the clock belongs to the stone

A small stone that passes during a week of hydrangea capsules could well have passed anyway, which is why the 1898 report of 120 calculi from one patient proves nothing. There is no fair trial period a reader can run on themselves for stone dissolution, because the herb's own advocates did not claim it.

When to stop

• Immediately, for fever, vomiting, worsening flank pain or inability to urinate.

• Immediately, for dizziness, chest tightness or nausea after a dose.

• Within the short window the label sets, if nothing has changed. The labels do not support open-ended use.

Onset of adverse effects

In the June 2008 Japanese leaf incidents, nausea, dizziness and vomiting began about 30 to 40 minutes after eating. That is leaf of a different species, but it is the only timed human exposure to the genus found for this issue.

Benefits of Taking Hydrangea Root

No benefit of H. arborescens root has been demonstrated in people. What can be said honestly is short:

• A long traditional record. Cherokee use, adoption by settlers and Eclectic physicians, and inclusion in the 1918 Dispensatory of the United States. Tradition shows what people used; it cannot show what worked.

• Animal kidney data for a relative. H. paniculata coumarins protected rodent kidneys in at least six drug-induced or immune injury studies published from 2012 to 2021. They are a reason to study the American root, not evidence that it does anything.

• Human trials of a different hydrangea. H. serrata leaf extract improved skin and body-weight measures in two 12-week Korean trials. They say nothing about urinary use.

A buyer who wants a measured result for stones, prostate or kidney health will not find one attached to this root.

Potential Negatives & Side Effects

Reported with oral use

Natural Medicines lists nausea, vomiting, diarrhea, dizziness and chest tightness, and notes possible stomach and intestinal irritation. The dizziness and chest symptoms trace back to the overdose warnings in King's (1898) and the 1918 Dispensatory. A PubMed search for this issue found no modern published case report of toxicity from oral H. arborescens root, which reflects how little anyone has looked as much as how safe it is.

The safety rating depends on which edition you read

RxList's reproduction of the Natural Medicines monograph calls more than 2 g of dried root "at a time" likely unsafe and long-term use likely unsafe. A consumer edition of the same database calls large amounts possibly unsafe and says more than 2 g "might cause dizziness and feelings of tightness in the chest." Both put the line at 2 g.

Contact allergy to the plant

Hydrangea is a documented, if uncommon, cause of allergic contact dermatitis, and the allergen has a name. B. M. Hausen reported hydrangenol, a dihydroisocoumarin, as "a strong contact sensitizer" in Contact Dermatitis in 1991, four years after he and D. P. Bruynzeel published a letter on hydrangea allergy in the same journal. Case reports go back at least to 1973 (Apted, Archives of Dermatology). The record since Hausen:

• Kuligowski and colleagues (Nijmegen, 1992) titled their report "a 10th case."

• Avenel-Audran and colleagues (2000) described 8 cases over 15 years in Angers, France, an area that produces almost 90% of French hydrangea seedlings. All patients reacted strongly to patch tests with stem and leaf, and hydrangenol was positive whenever it was tested. The typical picture was chronic, fissured eczema of the first three fingers.

• Rademaker (2003) reported two New Zealand commercial growers with hand and facial dermatitis that resolved with avoidance.

• Case reports followed from Amsterdam (De Rooij, 2006), an Italian florist (Romita, 2020) and an Italian paper asking whether hydrangea allergy is "underdiagnosed" (Lauriola and Corazza, 2021).

• In Odense, Denmark, 57 of 1,893 eczema patients patch tested from 2019 to 2023 (3%) were sensitized to some plant; hydrangea was among the culprits (Paulsen and Mortz, 2024).

These are people who grow, sell or arrange ornamental hydrangeas and react to the leaves, stems and flowers. Hydrangenol content of H. arborescens root has not been measured in any source found for this issue, so the allergy risk from swallowing the root is unknown rather than zero. Anyone already sensitized should not test it. One oddity: the 151-person H. serrata skin trial named hydrangenol as its active compound and reported no extract-related adverse reactions.

Interaction risk

The lithium interaction under Interactions is the one drug interaction any database names.

Deficiency Symptoms

No deficiency state exists for hydrangea or any of its constituents.

What hydrangea root addresses

Nothing the body runs short of. Umbelliferone and the other root coumarins have no recognized requirement, no reference intake, and no symptoms of absence.

Bottom line

Low intake of hydrangea root carries no penalty. The comparison point would be a real trace nutrient such as molybdenum, whose absence disrupts specific enzymes; nothing comparable exists for any hydrangea compound.

Toxicity Symptoms

At high intake

• Historical overdose (root): "dizziness of the head, oppression of the chest" (King's, 1898); "vertigo, oppression of the chest" (Dispensatory of the United States, 1918).

• Japanese leaf incidents, June 2008 (garden hydrangea leaves, not H. arborescens root): on June 13 in Tsukuba, Ibaraki Prefecture, 10 restaurant diners ate hydrangea leaves served with their food and 8 developed nausea and dizziness about 30 minutes later. On June 26 in Osaka, a man ate leaves placed under a rolled omelet at an izakaya and vomited, with facial flushing, about 40 minutes later. None became seriously ill, and all recovered within 2 to 3 days, according to a Food Safety Commission of Japan fact sheet. A Tokyo Metropolitan Government table of plant food poisonings lists 3 hydrangea incidents from 2003 to 2015.

• The culprit is unresolved. The Food Safety Commission sheet names hydracyanoside A, a nitrile glycoside, as the toxic component. Japan's health ministry, in its own risk profile, says the long-assumed cyanogenic glycosides are unconfirmed and that a suspected emetic alkaloid has not been identified. Febrifugine, an alkaloid that causes vomiting, has been isolated from H. macrophylla leaves (Ishih, Phytotherapy Research, 2003), though no study has tied it to these incidents. Tsukioka and colleagues (Journal of Natural Medicines, 2023) measured the cyanogenic glycoside taxiphyllin in H. macrophylla var. thunbergii leaves, found it varied more than threefold with harvest time and was mostly destroyed by processing, and suggested that cyanogenic glycosides are not what makes Sweet Hydrangea Leaf tea cause vomiting.

• Animals: the ASPCA lists vomiting, depression and diarrhea for H. arborescens in dogs, cats and horses, adding that "cyanide intoxication is rare." At the Milan poison control center in Italy, H. macrophylla ranked among the plants most often involved in domestic animal poisoning calls from 2000 to 2011, with dogs the species in 61.8% of plant calls (Caloni, Veterinary Record, 2013). From January 2015 to March 2019 the same center logged 932 animal poisoning calls, 95 of them plant exposures, and H. macrophylla was again among the three most reported plants (Bertero, Toxicon, 2021).

• Rodent acute toxicity (another species): a single oral dose of 5 g/kg of H. paniculata extract caused slow movement and huddling in mice at 2 hours, which soon resolved, with no abnormal signs over 14 days (Zhang, 2017). No equivalent test of H. arborescens root has been published.

Signs to reduce or stop

Dizziness or lightheadedness, a tight or heavy feeling in the chest, nausea, vomiting, diarrhea, facial flushing, or an itchy, cracked rash on the fingertips after handling the plant or the powder.

General note

Cyanide is the fear most people bring to hydrangea, and the record does not support it as the usual problem: the ASPCA describes gastrointestinal upset as the typical picture, the 2023 Kyoto work argues against cyanogenic glycosides as the cause of the tea poisonings, and no measured cyanide yield for H. arborescens root has been published. Bondurant's 1887 description of hydrangin (a glucoside that fluoresces blue in alkali and splits into glucose) is consistent with a coumarin glucoside, not a cyanide-releasing compound, and his report does not mention cyanide.

How Hydrangea Root Works

The proposed mechanisms are borrowed almost entirely from research on other species, and none of them involves dissolving a stone.

Coumarins and their metabolites

When rats are given H. paniculata coumarin glycosides by mouth, the circulating compounds are skimmin and its aglycone umbelliferone (7-hydroxycoumarin), along with esculetin (Phytomedicine, 2018 and 2021). In rodent kidneys and cultured kidney cells, these compounds reduce NF-κB activation, reactive oxygen species and TGF-β/Smad2/3 fibrosis signaling, and the 2021 work adds reduced complement C3 production in tubular cells. These are anti-inflammatory and antifibrotic effects in injured tissue, not effects on crystals.

The dose gap

The lowest rat dose of purified H. paniculata coumarins tested in those studies was 7.5 mg/kg. The Nature's Way daily direction, at the 2023 root assay, supplies roughly 6 mg of total coumarins, about 0.09 mg/kg for a 70 kg adult. Even after the standard body-surface conversion from rat to human (dividing by about 6.2), the rat dose corresponds to about 1.2 mg/kg, roughly 14 times the estimated capsule intake. The arithmetic is approximate, but it is not close.

Umbelliferone is not coumarin, and not warfarin

Umbelliferone is the 7-hydroxylated form of coumarin, the product of the main route by which humans metabolize coumarin itself. It lacks the 4-hydroxy structure that defines warfarin-type anticoagulants. "Contains coumarins" on a hydrangea fact sheet should not be read as "thins the blood" or as "carries the liver concerns of cassia coumarin."

The diuretic hypothesis

Natural Medicines attributes a possible increase in urine output to hydrangea's constituents. No study has measured it for H. arborescens, and the lithium warning rests on that unmeasured premise.

Hydrangenol

Hydrangenol is an isocoumarin found in H. macrophylla and H. serrata leaves. It drives the contact allergy described above, and Korean researchers credit it with the skin effects of H. serrata extract. Its presence and amount in H. arborescens root are unreported.

Synergistic Supplements

No combination containing hydrangea root has been tested in a human trial, so no synergy has been shown.

The historical pairing, and why it now reads as a warning

The best-documented combination is Lambert & Co.'s "Lithiated Hydrangea" from the 1880s, which paired the root with lithia. Today the one drug interaction that databases list for hydrangea is with lithium (see Interactions).

Typical modern blends

Hydrangea root usually appears inside multi-herb "kidney" or "stone" formulas. The FDA's 2017 letter to Years to Your Health quoted one such blend: agrimony, hydrangea root, marshmallow root, stone root, gravel root, lobelia and ginger root. Gravel root, corn silk, uva ursi, buchu, juniper and celery seed, the other common partners, each have their own issues in this archive. A blend makes it impossible to attribute either a benefit or a reaction to any single herb, and lobelia brings its own toxicity.

What actually has trial support for stones

Higher fluid intake, and prescription therapies chosen by stone type (for example potassium citrate for some calcium and uric acid stones), are the approaches urology guidelines rest on. Adding hydrangea to those adds an untested variable, not a partner.

Interactions & What NOT to Take

• Lithium (for example Lithobid): rated a moderate interaction by Natural Medicines. The concern is that a diuretic effect could reduce lithium clearance and raise lithium levels into the toxic range. It is theoretical, and no published case was found, but lithium has a narrow margin and the consequence would be serious.

• Loop and thiazide diuretics (furosemide, bumetanide, hydrochlorothiazide, chlorthalidone): a theoretical additive effect, built on the same unmeasured diuretic premise.

• Warfarin and direct oral anticoagulants (apixaban, rivaroxaban): no interaction report was found. Umbelliferone is not a 4-hydroxycoumarin, the chemical class of warfarin, so "coumarin content" is not by itself a bleeding signal.

• Cytochrome P450 substrates: no data exist on H. arborescens root and any drug-metabolizing enzyme. An absence of data is not evidence of safety.

• Other "stone" products at the same time: stacking several kidney blends multiplies unknowns and makes any reaction impossible to trace.

Do not take hydrangea root instead of seeking care for a stone that is causing fever, vomiting or blocked urine.

Quality, Testing & Adulteration

The identity problem is built into the name

"Hydrangea" on a label can mean four materially different things: H. arborescens root (the American supplement), H. paniculata stem (Chinese renal research), H. serrata or H. macrophylla leaf (Korean and Japanese products), or, since the 2015 reclassification, Hydrangea febrifuga, the herb sold for centuries as chang shan. Febrifugine, the chang shan alkaloid, was abandoned as an antimalarial drug because of diarrhea, vomiting and liver toxicity, according to a 2006 Journal of Medicinal Chemistry paper. Febrifugine has also been isolated from other hydrangeas, including H. umbellata, the leaves of the garden hydrangea H. macrophylla (Ishih, 2003) and the roots of H. chinensis (Khalil, 2003). One Australian university monograph lists febrifugine and isofebrifugine among H. arborescens constituents without a measured amount or primary source; this issue could not confirm it.

What a product listing can hide

The Nature's Way bottle names "Hydrangea arborescens" and "root." A third-party summary of the same product lists only "Hydrangea," with species and part blank. Herb Pharm's label adds "sustainably wildcrafted," a statement about sourcing that says nothing about identity testing. Wild versus cultivated supply is covered in the Honeybush issue.

Testing programs

No hydrangea root product carrying a USP Verified or NSF Certified mark turned up in research for this issue, and no ConsumerLab review of the category was found. Those programs, where they apply, confirm that the labeled ingredient and amount are present and that contaminants are under limits; none tests whether a herb works. No published HPTLC fingerprint or DNA barcode reference specific to H. arborescens root was found either. The 2023 Russian anatomy paper documents diagnostic microscopic features of the leaf (anomocytic stomata on the lower surface, calcium oxalate raphides, several hair types), and a 1974 Japanese study mapped calcium oxalate crystal patterns across Hydrangea leaves, but no reference method for powdered root was found.

Garden hydrangeas are studied as aluminum and lead accumulators (metals in botanicals are covered in the Iceland Moss issue); no measured metal results for H. arborescens root products were found.

Paperwork worth requesting from the seller

• The full Latin binomial (Hydrangea arborescens) and the plant part (root or rhizome), not just "hydrangea."

• The identity method actually run (microscopy, HPTLC or DNA) and the reference material it was compared against.

• Lead, cadmium, arsenic and mercury results with the limits applied, plus microbial counts.

• For extracts, the herb-to-solvent ratio and alcohol percentage. For any product claiming a marker, the method and result for total coumarins.

What you can verify without the seller's help

• The label names the species and the part. If it says only "hydrangea," put it back.

• The label makes no claim to "dissolve" stones; the FDA has treated that wording as an unapproved drug claim.

• A single serving stays well below 2 g of root equivalent. Both labels reviewed here do; a 15 g tea does not.

• The NIH Dietary Supplement Label Database (DSLD) lets you read the full label of many products before buying.

Special Considerations

Pets, horses and the plant in the yard

H. arborescens is a common yard and garden shrub (the 'Annabelle' type), and the ASPCA lists it as toxic to dogs, cats and horses, with vomiting, depression and diarrhea the usual signs. Milan poison center data put H. macrophylla among the plants most often involved in domestic animal calls in both 2000 to 2011 and 2015 to 2019. Dried hydrangea flowers in arrangements and spilled capsules are both within reach of a curious dog. The ASPCA Animal Poison Control Center and a veterinarian are the right first calls.

Gardeners, florists and nursery workers

The contact allergy reports cluster in people who handle hydrangeas for a living, often presenting as cracked fingertip eczema of the thumb, index and middle fingers. Gloves address the hazard; switching to a different hydrangea product does not.

Diners in Japan

Hydrangea leaves are sometimes used as a seasonal garnish under sashimi or omelet. Japan's health ministry says not to eat them.

Older adults

Lithium, diuretics and declining kidney function are all more common with age, and all three are the situations where an untested diuretic claim matters most.

Children

No safety data exist. A third-party label listing that extends use to children 4 years and older is not supported by any published study.

Research Status & Evidence Quality

Evidence tiers

• Human randomized trials of H. arborescens: none, for any indication.

• Human clinical reports on oral root: 19th century anecdotes only, including the 120-calculi report (King's, 1898) and two uncontrolled gout cases with Lithiated Hydrangea (1885).

• Animal studies: at least six rodent kidney-injury studies from 2012 to 2021, all on H. paniculata. None on H. arborescens.

• Human trials of another hydrangea: two 12-week randomized trials of H. serrata leaf extract (n = 151 and 93), for skin and body weight.

• Chemistry: one modern quantitative analysis of H. arborescens root (2023: total coumarins 0.41%) and 19th century isolations of hydrangin (1887, 1889).

• Safety: contact allergy reports from 1973 to 2024; the June 2008 Japanese leaf incidents (9 people ill across two events); poison center animal data from Milan (2000 to 2019); ASPCA listing; Natural Medicines ratings.

Research Limitations

• The literature mixes species freely. Consumer articles cite H. paniculata kidney studies as evidence for H. arborescens root.

• No product is standardized, so even a positive trial would be hard to reproduce on the shelf.

• The 2 g safety threshold has no cited case series behind it in the database text reviewed for this issue; the database's consumer record shows a last update on December 12, 2014, though it was reviewed again on March 23, 2026.

• No source reviewed for this issue reports the cyanogenic glycoside or hydrangenol content of H. arborescens root.

• The cause of the Japanese leaf poisonings remains disputed between cyanogenic glycosides and other constituents.

Summary & Key Takeaways

Bottom Line

Hydrangea root (Hydrangea arborescens) is a 19th century bladder remedy with no published human trial behind it, no standardized product on the shelf, and a 2 g single-dose safety line that sits at its own old standard dose. The case for buying it is tradition. The case against is a century-old overdose warning, a lithium interaction, largely unmeasured chemistry, and a plant the ASPCA lists as toxic to pets. For stones, an analysis of the stone itself and guideline-based care do what this root has never been shown to do.

Key Safety Points

• Overdose causes dizziness and chest oppression, a warning repeated from 1898 to today; Natural Medicines draws the line at more than 2 g of dried root at a time and rates long-term use as likely unsafe.

• Avoid with lithium, in pregnancy and breastfeeding, and in children.

• Hydrangea plants cause allergic contact dermatitis, with hydrangenol identified as a strong sensitizer.

• The ASPCA lists H. arborescens as toxic to dogs, cats and horses.

• A stone with fever, vomiting or blocked urine needs emergency care, not an herb.

Special Note

When you read "hydrangea" in a study, a fact sheet or on a bottle, check the species and the plant part before you believe anything attached to it.

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Researched and drafted with AI assistance. Every claim verified against primary sources and human-reviewed before publication. Last reviewed: November 7, 2026. Corrections: reply to any issue.

This issue is for education only and is not medical advice. If you take any medication or have a diagnosed condition, talk with a clinician before starting, stopping or changing a supplement.