No reliable clinical evidence supports the use of “vitamin B17” as a cancer treatment. The substance in question, amygdalin, is a naturally occurring compound found in the seeds and pits of many fruits, and laetrile is a semi-synthetic version of it. Despite decades of promotion by alternative-medicine advocates, systematic reviews have found zero randomized controlled trials demonstrating any benefit against cancer, while the documented risks include potentially fatal cyanide poisoning. The story behind this supposed cancer cure is a case study in how unproven remedies persist long after the science has weighed in.
What “Vitamin B17” Actually Is
The first thing to know is that “vitamin B17” is not a vitamin. Vitamins are nutrients your body requires in small amounts to function properly, and amygdalin does not meet that definition by any recognized nutritional or medical authority. The name was coined in the 1970s as a marketing strategy to make the substance sound like a natural, essential nutrient rather than what it is: a cyanogenic glycoside, a type of plant chemical that releases hydrogen cyanide when broken down.
Amygdalin occurs naturally in the seeds of apricots, peaches, bitter almonds, and dozens of other plants. In nature, this cyanide-releasing ability is a defense mechanism: when an insect or animal chews on the seed, the plant’s enzymes break amygdalin apart and release cyanide, discouraging the herbivore from eating more.1PubMed Central. Plant cyanogenic glycosides: from structure to properties and potential applications Laetrile, the form typically sold or administered as a cancer therapy, is a semi-synthetic derivative of amygdalin. The two names are often used interchangeably, though they are chemically distinct.2PubMed. Anticancer Attributes and Multifaceted Pharmacological Implications of Laetrile and Amygdalin
The Proposed Anti-Cancer Mechanism
The theory behind laetrile as a cancer treatment goes roughly like this: cancer cells supposedly contain high levels of an enzyme called beta-glucosidase, which breaks amygdalin down and releases cyanide directly at the tumor site. Meanwhile, normal cells supposedly have plenty of another enzyme, rhodanese, which can detoxify that cyanide before it causes harm. In this framework, amygdalin acts like a “selective poison” that kills cancer cells while sparing healthy tissue.
It is an elegant story, and it is wrong. Research going back to the early 1980s showed that cancer tissues actually contain low levels of beta-glucosidase compared to normal liver and small intestine tissue. Even more damaging to the theory, cancer cells contain rhodanese in amounts comparable to liver and kidney cells, meaning they are not uniquely vulnerable to cyanide at all.3PubMed. The case against laetrile: the fraudulent cancer remedy The selective-toxicity idea has no biochemical foundation. Cyanide released from amygdalin does not preferentially target tumor cells. It poisons whatever tissue it reaches.
How Amygdalin Turns Into Cyanide in Your Body
If the enzyme levels in cancer cells do not support the proposed mechanism, where does the cyanide actually come from? The answer turns out to be your gut. When amygdalin is swallowed, bacteria in the intestines do the job of breaking it down and releasing hydrogen cyanide into the bloodstream. This was demonstrated in a striking experiment comparing normal rats with germ-free rats (animals raised without any intestinal bacteria). Normal rats given oral amygdalin developed lethal blood cyanide levels and often died within hours. Germ-free rats given the same dose showed almost no cyanide in their blood and experienced no symptoms.4Biochemical Pharmacology. Role of the gastrointestinal microflora in amygdalin (laetrile)-induced cyanide toxicity
More recent work has identified specific gut bacteria involved in breaking amygdalin apart and generating cyanide.5PubMed Central. Impact of intestinal microbiota on metabolic toxicity and potential detoxification of amygdalin This matters for a practical reason: the toxicity of oral amygdalin is partly unpredictable because it depends on the unique composition of a person’s gut microbiome. Two people taking the same dose could experience very different levels of cyanide exposure. Intravenous laetrile bypasses the gut and is somewhat less acutely toxic, but it still introduces cyanide-generating compounds into the body without any proven benefit.
What the Clinical Evidence Shows
The most authoritative test of laetrile in humans was a phase II clinical trial published in the New England Journal of Medicine in 1982. The study enrolled cancer patients who received amygdalin intravenously and then orally, alongside a so-called “metabolic therapy” diet. The results were unambiguous: no patient was cured, no patient saw their cancer stabilize, and there was no improvement in symptoms or life span. Several patients developed symptoms of cyanide toxicity, and some had blood cyanide levels approaching the lethal range. The authors concluded flatly that amygdalin is “a toxic drug that is not effective as a cancer treatment.”6PubMed. A clinical trial of amygdalin (Laetrile) in the treatment of human cancer
Since that trial, no one has conducted a randomized controlled trial of laetrile or amygdalin for cancer, which is itself telling. A Cochrane systematic review, the gold standard for evaluating medical evidence, searched for any controlled trials and found none. The review concluded that “the claims that laetrile or amygdalin have beneficial effects for cancer patients are not currently supported by sound clinical data” and that the risk-benefit balance “is therefore unambiguously negative.”7Cochrane Database of Systematic Reviews. Laetrile treatment for cancer A separate systematic review that examined 36 publications, including case series and case reports, reached the same conclusion: none proved effectiveness.8PubMed. Laetrile for cancer: a systematic review of the clinical evidence
This is not a case of “more research is needed.” The compound has been tested, reviewed, and reviewed again over four decades. The evidence base is not thin because scientists are ignoring it. It is thin because what testing has been done showed no benefit and clear harm, giving researchers no scientific reason to pursue further trials.
Real Cases of Cyanide Poisoning
The danger of amygdalin is not theoretical. Published case reports document exactly what happens when people take this substance, and the outcomes range from serious illness to death. A 41-year-old woman in the United States ingested apricot kernels purchased at a health food store and within 20 minutes became weak and had difficulty breathing. By the time she reached the emergency department, she was comatose and hypothermic. She survived only because doctors recognized cyanide poisoning and administered antidotes promptly.9PubMed. Acute cyanide toxicity caused by apricot kernel ingestion
Children are especially vulnerable. A 28-month-old girl who ate apricot seeds while sitting with her father lost consciousness and began seizing. Her blood cyanide level exceeded 3 mg/L within hours, a concentration well into the lethal range. Despite intensive care, she died on the 22nd day of hospitalization.10American Journal of Case Reports. Fatal cyanide poisoning in a child, caused by eating apricot seeds These are not outlier events. They are the predictable consequences of consuming a substance that releases cyanide in the human digestive system.
Emergency treatment for cyanide poisoning from amygdalin typically involves hydroxocobalamin (a form of vitamin B12 that binds cyanide) or a combination of amyl nitrite and sodium thiosulfate. In one case, a woman who ingested amygdalin tablets was critically ill but recovered fully after receiving hydroxocobalamin.11PubMed Central. Physician Beware: Severe Cyanide Toxicity from Amygdalin Tablets Ingestion The fact that specific antidotal protocols exist for this exact scenario tells you something about how often it happens.
Drug Interactions That Increase the Risk
People drawn to laetrile often embrace a broader alternative health philosophy, and that creates a compounding hazard. One well-documented interaction involves high-dose vitamin C supplements. Your body detoxifies cyanide by converting it to a less harmful compound called thiocyanate, and this process depends on cysteine, a sulfur-containing amino acid. Large doses of vitamin C can deplete cysteine stores, which could impair your ability to handle the cyanide released from amygdalin.12Medical Hypotheses. Conjoint use of laetrile and megadoses of ascorbic acid in cancer treatment: Possible side effects Since many alternative cancer protocols recommend both laetrile and megadose vitamin C, this is a genuinely dangerous combination that the people most likely to try it are also most likely to encounter.
Why People Still Seek It Out
Given the weight of evidence, it is reasonable to wonder why anyone still pursues laetrile. Part of the answer is that misinformation about cancer treatments is extraordinarily common. In a survey of over 600 U.S. adults, including people with cancer diagnoses and caregivers, more than half reported seeing cancer treatment misinformation on social media. Among those with a cancer diagnosis, about 70% had encountered such content. Roughly a quarter of all participants had received advice about alternative ways to treat or cure cancer, and the rate was even higher among cancer patients themselves, at close to half.13JMIR Publications. Exposure and Reactions to Cancer Treatment Misinformation and Advice: Survey Study Perhaps most troubling, about 70% of participants thought cancer treatment misinformation on social media was true at least some of the time.
Laetrile also benefits from a persistent conspiracy narrative: the idea that pharmaceutical companies and regulatory agencies are suppressing a natural cure to protect their profits. This framing is almost impossible to disprove to a believer, because any evidence against laetrile can be folded into the narrative as further proof of the cover-up. The “vitamin B17” branding plays directly into this by suggesting that the substance is something your body needs and the medical establishment refuses to acknowledge.
When Patients Do Not Tell Their Doctors
A related problem is that many cancer patients who try alternative remedies never mention it to their oncologist. A systematic review of 21 studies found that between 20% and 77% of cancer patients using complementary and alternative therapies did not disclose this to their doctors. The most common reasons were that the doctor never asked, the patient expected the doctor to disapprove, or the patient did not think it was relevant to their conventional treatment.14PubMed Central. Cancer patient disclosure and patient-doctor communication of complementary and alternative medicine use: a systematic review
This nondisclosure is dangerous in general, but it is especially dangerous with amygdalin. A doctor who does not know a patient is taking laetrile or eating apricot kernels daily cannot monitor for cyanide exposure, cannot adjust treatment plans to account for potential interactions, and cannot respond quickly if symptoms of toxicity appear. If you or someone you know is considering amygdalin, telling the treatment team is not optional. It is a safety issue.
The Regulatory Landscape
Laetrile is not approved as a cancer treatment by the U.S. Food and Drug Administration, and it is banned from interstate commerce in the United States. In Canada, the position has been similarly firm since the 1970s. Repeated testing by major research institutions, including the National Cancer Institute and the Sloan-Kettering Institute, failed to show that amygdalin could cure, control, or even alleviate cancer.15Canadian Medical Association journal. Laetrile: Canada’s legal position firm but pressure in the South grows
That said, the substance remains available in some countries, can be purchased online, and is sold in the form of raw apricot kernels marketed as health foods. In parts of Mexico, clinics have historically offered laetrile infusions to cancer patients who travel across the border from the United States specifically to obtain them. The practical reality is that regulatory bans have limited, but not eliminated, access. Anyone sufficiently motivated to find amygdalin or laetrile can do so, which is why clear public communication about its risks remains important.
What About the Lab Studies
Advocates sometimes point to laboratory research showing that amygdalin kills cancer cells in a dish. These studies do exist, and some show real cytotoxic effects on cell lines. Researchers have even explored encapsulating amygdalin in nanoparticles to improve its delivery to tumor cells.16International Journal of Biological Macromolecules. Evaluation of amygdalin-loaded alginate-chitosan nanoparticles as biocompatible drug delivery carriers for anticancerous efficacy But cell-culture experiments are the very earliest stage of drug development. Thousands of substances kill cancer cells in a petri dish, including bleach and boiling water. The question is whether a compound can selectively target cancer in a living human body at doses that do not cause unacceptable harm. For amygdalin, every attempt to answer that question in humans has come back negative.
The nanoparticle research is genuine science, but it is basic research exploring whether delivery technology could hypothetically make amygdalin more targeted. It does not constitute evidence that amygdalin works as a cancer therapy. The leap from “kills cells in a dish” to “treats cancer in people” is enormous, and most compounds that make it through the first step never survive the second. Amygdalin failed at the second step decades ago, and nothing in the current laboratory research changes that picture for patients today.
Apricot Kernels Sold as Food
One of the more insidious ways people are exposed to amygdalin is through “bitter” apricot kernels marketed as a superfood or health supplement. These are the seeds found inside apricot pits, and they contain substantial concentrations of amygdalin. They are sold online and in some health food stores, often with carefully worded disclaimers that stop short of making explicit cancer claims but strongly imply health benefits. Social media posts and alternative health blogs fill in the gaps by directly recommending them for cancer prevention or treatment.
Eating a handful of these kernels is not the same as eating a few almonds. Each kernel can contain enough amygdalin to release a meaningful dose of cyanide once gut bacteria go to work on it. The European Food Safety Authority has assessed the acute health risks of raw apricot kernels and found that even small numbers can push adults toward potentially harmful cyanide exposure. For children, the margin of safety is even narrower, as the fatal case of the toddler mentioned earlier illustrates.
The kernels are legal to sell in many places as a food product, which creates a confusing signal: if they are available in a store next to other seeds and nuts, consumers understandably assume they are safe to eat in similar quantities. They are not. If you encounter apricot kernels marketed with health claims, treat those claims with the same skepticism you would apply to any unregulated product promising to treat a serious disease.
How “Vitamin B17” Got Its Name
The “vitamin” label was deliberately chosen. In the 1970s, Ernst Krebs Jr., who promoted laetrile as a cancer treatment, began referring to amygdalin as vitamin B17. This was a strategic move. If amygdalin were classified as a vitamin, it could potentially sidestep the FDA’s drug regulations and be sold as a dietary supplement. The framing also implied that cancer was a deficiency disease, something caused by not getting enough of a natural substance, which made the “treatment” feel intuitive and nonthreatening.
No scientific body has ever recognized amygdalin as a vitamin. There is no known deficiency syndrome associated with a lack of amygdalin, and your body does not require it for any metabolic process. The B17 designation is pure marketing, but it has been remarkably sticky. Decades later, you can still find the term used uncritically on product labels, in online forums, and across social media platforms, giving a veneer of nutritional legitimacy to a compound that is neither a nutrient nor a medicine.