Amygdalin/Laetrile

What is Amygdalin?

Amygdalin is a cyanogenic diglycoside from the kernels of stone fruits, most abundantly bitter almond and apricot. Cleave off its sugars and it decomposes into benzaldehyde and hydrogen cyanide, 5.9 percent of it by mass. That is not a contaminant, it is the seed's chemical defense against anything that chews it.

Sold since the 1950s as Laetrile and later as "vitamin B17," it is the most thoroughly tested and most thoroughly rejected alternative cancer therapy in American medical history. The National Cancer Institute funded the trials. They were negative, patients developed cyanide toxicity, and it is still on sale.

Common Names

• Amygdalin

• Laetrile, a trade name; the US-patented product was mandelonitrile beta-glucuronide, the Mexican product amygdalin itself

• "Vitamin B17," a marketing designation, not a recognized nutrient

• Bitter apricot kernel, bitter almond extract

Primary Active Compounds

• Amygdalin, C20H27NO11, a diglycoside of mandelonitrile carrying two glucose units

• Prunasin, the monoglycoside formed when the first sugar is removed

• Mandelonitrile, the unstable aglycone that falls apart into benzaldehyde and cyanide

• Emulsin, the plant's own beta-glucosidase, in the same kernel

Key Note

Amygdalin occurs in the seeds of Prunus armeniaca (apricot), Prunus dulcis var. amara (bitter almond), Prunus persica (peach), cherry, and plum. The fruit flesh is safe. The hazard is the kernel inside the pit.

Everything below follows from one fact: this is a delivery system for cyanide, and your gut bacteria are good at opening it.

Primary Functions & Benefits

Amygdalin has no established function in human physiology and no demonstrated benefit for any condition. What it does is narrow and well characterized.

• A beta-glucosidase removes one glucose to yield prunasin, a second yields mandelonitrile, which decomposes into benzaldehyde and hydrogen cyanide.

• The cyanide binds cytochrome c oxidase in the mitochondrial electron transport chain, halting aerobic ATP production. Lactate accumulates, which is why cyanide poisoning presents with severe lactic acidosis.

The claimed benefit, selective destruction of cancer cells, was tested and did not occur. Section 12 covers why.

Who Should Take Amygdalin

No one. No population has evidence supporting use, and no dose has demonstrated benefit.

The more useful question is who is being sold it.

• People with advanced or metastatic cancer told standard options are exhausted. Wanting to keep acting when the medical system has run out of moves is not gullibility.

• People recently diagnosed and frightened, told an inexpensive natural compound was suppressed by industry.

• People with no cancer at all, taking kernels preventively. The cyanide exposure is identical.

The real cost is not only the cyanide. The measurable harm in the record is delayed or abandoned effective treatment. Patients who chose laetrile over surgery, chemotherapy, or radiation while their disease was still treatable lost that window permanently. The Supreme Court addressed this in United States v. Rutherford (442 U.S. 544, decided June 18, 1979), rejecting the argument that safety and effectiveness standards do not apply to dying patients. A terminal diagnosis is what makes a person a target.

If you are in the first group, the useful conversation is with your oncology team about trial enrollment and palliative care.

Who Should AVOID or Use Caution

Contraindications

• Everyone. Amygdalin and laetrile should not be taken at any dose, by any route.

• Children carry the highest risk because dose scales with body weight. A 2015 case in Wiener Medizinische Wochenschrift described a 4-year-old boy with metastatic ependymoma whose parents gave him intravenous and oral "vitamin B17" plus apricot kernels for about a week. He arrived with a Glasgow Coma Scale of 3, severe lactic acidosis, and markedly elevated serum cyanide, and recovered after sodium thiosulfate.

• Pregnancy and breastfeeding. Cyanide crosses the placenta and amygdalin is teratogenic in animal models.

Use Caution

• Raw bitter apricot kernels sold as a health food carry the same hazard as the pills, as do bitter almonds and raw peach or cherry kernels.

• Any household storing kernels loose where a child can reach them.

Critical Safety Point

Poisoning from oral amygdalin is not instantaneous. Bacterial hydrolysis takes time, so symptoms can appear hours later, and feeling fine at hour one means nothing. Contact Poison Control rather than waiting. Hydroxocobalamin and sodium thiosulfate work best early.

Recommended Dosages

There is no recommended dosage. What follows is what is on the market and what trials used, so you can recognize the products.

What clinics have administered

Moertel's 1982 phase II trial gave 4.5 g/m² intravenously for 21 days, then 0.5 g orally four times daily, with a comparison arm at 7 g/m².

What is sold to consumers

Amygdalin and "B17" tablets come at 100 mg and 500 mg, with vendors suggesting multiple tablets daily. Raw kernels sell loose by the bag, in capsules, and as powder.

What sellers recommend against the safety assessment

EFSA's 2016 opinion documented online sellers promoting 10 kernels per day for the general population and up to 60 per day for people with cancer. The same opinion set an acute reference dose of 20 micrograms of cyanide per kilogram of body weight, 25-fold below the lowest reported lethal dose. An adult reaches that limit at roughly three small kernels, about 370 mg of kernel material, a toddler at about 60 mg, half of one small kernel.

Duration

Not applicable. There is no duration at which this becomes appropriate.

Timing & Administration

This is not about optimizing absorption. It is about which presentation kills people, and the answer runs opposite to intuition.

• Oral is the more toxic route. Intestinal bacteria produce abundant beta-glucosidase and meet the full swallowed dose.

• The animal data isolate the mechanism. Germ-free rats given oral amygdalin showed no adverse effects and normal blood cyanide. Conventional rats on the same dose developed lethargy and convulsions with elevated cyanide. The difference was gut flora.

• Plant enzymes compound it. In the phase I trial, two of six patients developed cyanide poisoning symptoms after eating raw almonds while on oral amygdalin.

• Taking it with food, fasted, or in divided doses changes none of this.

Benefits of Taking Amygdalin

None have been demonstrated in humans. This is not thin evidence awaiting confirmation. It was tested under federal sponsorship and failed.

• The 1982 New England Journal of Medicine trial by Moertel and colleagues treated 178 patients with amygdalin plus the full "metabolic therapy" package of diet, enzymes, and vitamins. Among 175 evaluable patients, one partial response was recorded, in a gastric carcinoma, lasting 10 weeks. By the end of the intravenous course, 54 percent had measurable progression. By seven months, all had progressed. The authors concluded that amygdalin is a toxic drug not effective as a cancer treatment.

• The 2015 Cochrane review found no randomized trials of laetrile in cancer meeting inclusion criteria, out of more than 200 references screened, and concluded the risk-benefit balance is unambiguously negative.

• Cell-culture papers reporting that amygdalin kills tumor cell lines keep appearing. Cyanide kills cells in a dish. That does not distinguish a therapy from a poison.

Potential Negatives & Side Effects

The adverse effects of amygdalin are cyanide's, tracking dose and route.

• Early: nausea, vomiting, headache, dizziness, confusion, weakness.

• Cardiovascular and respiratory: dyspnea, hypotension, tachycardia progressing to bradycardia, cyanosis of skin and mucous membranes.

• Metabolic: severe lactic acidosis, the fingerprint of blocked mitochondrial respiration.

• Neurological: agitation, stupor, seizures, coma, then cardiovascular collapse and death.

• Chronic exposure: the FDA's May 24, 2024 warning on apricot seed products flags long-term neurological damage including vision impairment, hearing loss, and loss of balance. That injury does not necessarily reverse.

Deficiency Symptoms

Amygdalin is not an essential nutrient, so there is no deficiency state and no deficiency symptoms. That is the core of the claim laetrile was sold on. Krebs Jr. asserted cancer is a deficiency disease of "vitamin B17." No such deficiency has ever been produced in any organism.

What amygdalin addresses

Nothing. There is no condition it has been shown to help in humans.

Bottom line

A compound cannot be deficient if the body has no use for it. The absence of a deficiency state is the test the "vitamin" label never passed.

Toxicity Symptoms

At high intake

Acute cyanide poisoning, the progression listed in section 9, ending in seizures, coma, and cardiovascular collapse. Onset after oral dosing may lag by hours.

Signs to reduce or stop

There is no "reduce" here. Any symptom after ingesting amygdalin, laetrile, or bitter kernels, including a headache you would otherwise ignore, is a reason to stop and seek assessment the same day. Say the word cyanide, because clinicians will not suspect it unless you name it.

General note

In 2005 in Annals of Pharmacotherapy, a 68-year-old woman took 3 g of amygdalin while on her usual 4,800 mg of daily vitamin C and arrived with a reduced Glasgow Coma Scale, seizures, and lactic acidosis requiring intubation. She responded to hydroxocobalamin. A 2017 report in Case Reports in Emergency Medicine documented severe cyanide toxicity from amygdalin tablets alone. This is what the product does when taken as directed.

How Amygdalin Works

The mechanistic claim behind the laetrile movement sounds plausible and is wrong in a specific, checkable way.

• The claim: tumor tissue contains elevated beta-glucosidase, which releases cyanide inside the tumor, while normal tissue is protected by high rhodanese, which converts cyanide to thiocyanate. Cancer cells are said to be rhodanese-poor and killed selectively.

• Problem one, the enzyme is not where the claim needs it. Newmark and colleagues assayed beta-glucosidase activity across tissues and detected no glucose release from amygdalin or prunasin in any human neoplastic tissue examined, while rat and human small intestinal mucosa showed high activity. The enzyme is concentrated in your gut, not your tumor.

• Problem two, cyanide does not stay put. Even if a tumor liberated it locally, hydrogen cyanide is small, freely diffusible, and enters circulation immediately.

• Problem three, rhodanese distribution does not deliver the claimed selectivity. Normal and malignant tissue do differ in rhodanese and glucuronidase levels, the grain of truth the claim is built on. But tested directly, laetrile showed no selective killing of human leukemia cell lines relative to normal bone marrow.

• What actually happens: colonic bacteria cleave what you swallow, cyanide enters your bloodstream and binds cytochrome c oxidase throughout your body. Your tumor is not a participant.

Synergistic Supplements

There are none. Amygdalin has no demonstrated benefit, so there is nothing to potentiate. Several products sold alongside it increase the danger.

• High-dose vitamin C, covered in section 14, the most important item here.

• Proteolytic enzyme blends, standard in the "metabolic therapy" package laetrile is sold inside.

One piece of biochemistry runs the other way. Rhodanese needs a sulfur donor, which is why sodium thiosulfate is a cyanide antidote. That is emergency medicine, not a supplement.

Interactions & What NOT to Take

• High-dose vitamin C. This is the interaction to know. Vitamin C increases the in vitro conversion of amygdalin to cyanide and depletes the cysteine the body needs to detoxify it. More cyanide made, less capacity to clear it. The 2005 case in section 11 is what that looks like. Both products are marketed to the same buyer, often on the same website.

• Raw almonds, bean sprouts, and crushed fresh fruit seeds. These supply plant beta-glucosidase directly, as the phase I trial showed.

• Anything that increases gut fermentation, including high-dose probiotics, would be expected to increase cyanide liberation from an oral dose. That is predicted mechanistically, not quantified.

• All conventional cancer treatment. The most damaging interaction on record is not chemical. It is substitution.

Special Considerations

• Legal status in the United States. Laetrile has never been FDA-approved. After Rutherford, the Tenth Circuit upheld the ban on interstate shipment in 1980, and FDA does not accept amygdalin as a lawful dietary ingredient. On May 24, 2024 it warned that specific apricot seed products contained amygdalin at levels that could cause fatal cyanide toxicity.

• Cross-border clinics. Laetrile is still given in Mexican clinics and some US clinics outside FDA oversight, often for tens of thousands of dollars.

• The family business. Ernst T. Krebs Sr. and Jr. also named and promoted pangamic acid as "vitamin B15," another compound with no established metabolic role. The same naming strategy applied twice is a pattern.

Research Status & Evidence Quality

Strong Evidence For

• Amygdalin releases hydrogen cyanide in the human body, more from the oral route than the intravenous.

• Amygdalin is not effective as a cancer treatment, established by NCI-sponsored trials and reaffirmed by systematic review.

• Amygdalin causes cyanide poisoning at commercially marketed doses, in adults and children.

Moderate Evidence For

• High-dose vitamin C increases the toxicity of a given amygdalin dose, from in vitro conversion data plus case reports rather than controlled study.

• Chronic low-level cyanide exposure from repeated kernel eating produces neurological injury, extrapolated from cyanide toxicology rather than prospective study.

Emerging / Preliminary Evidence For

• Nothing therapeutic. The in vitro cytotoxicity reports are dish findings for a compound that liberates cyanide.

Research Limitations

• The 1982 trial was non-randomized with no placebo arm. That limits it as general efficacy evidence, but no control arm was needed to read a result that stark.

• Cochrane found zero qualifying randomized trials. This is not a gap awaiting funding. The research was done, at public expense, and it answered the question.

Summary & Key Takeaways

Amygdalin is a cyanide prodrug renamed "vitamin B17" to escape drug rules, and the renaming was the most successful part of the product. When the National Cancer Institute tested it, one partial response was recorded and every patient progressed within seven months. Nothing since has changed that.

Bottom Line

Do not take amygdalin, laetrile, "vitamin B17," or raw bitter apricot kernels, and do not give them to a child. There is no dose with demonstrated benefit and no safe route, and the oral form sold to consumers is the more toxic one.

Key Safety Points

• EFSA's acute cyanide reference dose is reached at roughly three small apricot kernels for an adult and half of one for a toddler. Sellers recommend 10 a day, and 60 for people with cancer.

• High-dose vitamin C increases cyanide release from amygdalin and depletes the cysteine needed to clear it.

• Symptoms after oral dosing can be delayed by hours. Call Poison Control and say the word cyanide.

• The largest documented harm is treatment delayed or abandoned while a cancer was still treatable.

Special Note

The B17 story shows what a name can do that a molecule cannot. Calling a cyanide-releasing glycoside a vitamin invented a deficiency disease that does not exist, without a single experiment. When a supplement's name asserts a category, ask who assigned it and what evidence was submitted. If the seller assigned it, the name is the product.