Vitamin B17: Amygdalin, Cyanide, and Cancer Claims

“Vitamin B17” is not actually a vitamin. It is a commercial and alternative-medicine label for amygdalin, a naturally occurring compound found in the seeds and kernels of many fruits, most famously apricot pits and bitter almonds. No major scientific or regulatory body recognizes it as a nutrient the body needs, and its most prominent use, as an unproven cancer treatment marketed under the name “laetrile,” has been studied and found ineffective in clinical settings while carrying a real risk of cyanide poisoning.

What Amygdalin Actually Is

Amygdalin belongs to a family of compounds called cyanogenic glycosides, meaning it has a sugar molecule bonded to a structure that can release hydrogen cyanide under the right conditions. It occurs naturally in the seeds of plants in the Rosaceae family, including apricots, peaches, bitter almonds, cherries, and plums.¹ Seeds from Rosaceae species contain substantially more amygdalin than seeds from other plant families. In a survey of commercially available seeds and kernels in the UK, Rosaceae seeds contained roughly 0.1 to 17.5 milligrams per gram, while seeds from unrelated species ranged from 0.01 to 0.2 milligrams per gram.²

A laboratory analysis of 18 market samples of apricot kernels and almonds found amygdalin concentrations spanning an enormous range, from 2 to 24,000 micrograms per gram, with corresponding estimated cyanide content ranging from 0.2 to 1,420 micrograms per gram.³ That wide spread matters because someone eating a handful of bitter apricot kernels has no way to tell whether they are getting a low-amygdalin batch or a high one.

Why It Is Called a Vitamin

The “vitamin B17” label traces back to Ernst T. Krebs Jr., who in the mid-twentieth century promoted amygdalin and a semi-synthetic derivative he called laetrile as cancer treatments. Krebs argued that amygdalin was an essential nutrient and that cancer resulted from its deficiency, a framing that made the substance sound like an ordinary health supplement rather than an unapproved drug. No nutritional science supports this. Vitamins are, by definition, organic compounds the body requires in small amounts for normal metabolic function and cannot produce on its own. Amygdalin meets none of those criteria. The body does not use it in any known metabolic pathway, and no deficiency disease results from its absence. The “B17” label persists in health-food marketing and on some supplement packaging, but it is a marketing term, not a biochemical designation.

How Amygdalin Turns Into Cyanide

The danger of amygdalin comes from what happens after you swallow it. When crushed or chewed seeds are eaten, enzymes in the plant tissue and in your gut bacteria break the amygdalin molecule apart, releasing hydrogen cyanide.⁴ The amount of cyanide released depends partly on the composition of a person’s gut bacteria, which varies from individual to individual. That variability makes it genuinely hard to predict how much cyanide any given person will absorb from a set number of kernels.

Cyanide is toxic because it shuts down the machinery cells use to produce energy. Specifically, it binds to cytochrome c oxidase, a critical enzyme in the mitochondrial chain that converts oxygen into usable energy. Laboratory measurements show that when roughly 60 percent of this enzyme is blocked, cells can no longer consume oxygen normally.⁵ In severe poisoning, the result is essentially internal suffocation: the blood carries plenty of oxygen, but the cells cannot use it.

This is, ironically, the same chemical defense the plant evolved. Cyanogenic glycosides exist in seeds and leaves as a defense against insects and other herbivores. When an insect chews through plant tissue, compartmentalized enzymes meet the stored glycosides and generate a burst of cyanide, deterring or killing the attacker.⁶ Some specialized insects have evolved counter-adaptations to tolerate or even co-opt these compounds, but humans have not.⁷

How the Body Detoxifies Small Amounts of Cyanide

Humans encounter trace amounts of cyanide from many foods and even from cigarette smoke, so the body does have a built-in detoxification system. The liver enzyme rhodanese (also called thiosulfate-cyanide sulfurtransferase) converts cyanide into thiocyanate, a much less toxic compound that is then excreted in urine.⁸ This enzyme is involved in broader sulfur metabolism and also plays roles in maintaining iron-sulfur clusters and other cellular housekeeping.⁹

The catch is that rhodanese can only handle a limited throughput. Eating a few apple seeds or a small number of cooked stone-fruit products is well within the liver’s capacity. But swallowing a therapeutic dose of amygdalin supplements, or chewing through a pile of raw apricot kernels, can easily overwhelm the system. The detox pathway was shaped by incidental dietary exposure, not by someone intentionally concentrating the compound.

The Cancer Treatment That Never Panned Out

Proponents of laetrile (the semi-synthetic form of amygdalin) claimed for decades that it selectively killed cancer cells while leaving healthy cells unharmed. The theory was that cancer cells supposedly contained high levels of an enzyme that would release cyanide specifically at tumor sites, while healthy cells contained enough rhodanese to neutralize it. This sounded plausible enough to generate intense public demand in the 1970s and early 1980s, and tens of thousands of Americans traveled to clinics in Mexico to receive laetrile treatments.

The National Cancer Institute eventually funded a clinical trial, published in the New England Journal of Medicine in 1982, to test whether amygdalin had any effect against cancer in humans. The results were unambiguous: no benefit was observed in terms of tumor shrinkage, symptom improvement, or survival. Several patients showed signs of cyanide toxicity, with blood cyanide levels in some cases approaching the lethal range. The authors concluded plainly that amygdalin is “a toxic drug that is not effective as a cancer treatment.”¹⁰

Since that trial, no controlled clinical study has ever demonstrated a benefit. A Cochrane systematic review, the gold standard for evidence synthesis, assessed all available clinical data and found that claims of benefit “are not currently supported by sound clinical data,” while the risk of cyanide poisoning, especially from oral ingestion, was considerable. The review concluded that the risk-benefit balance is “unambiguously negative.”¹¹ A separate systematic review examined 36 published reports, including case series and individual case reports, and found no controlled trials at all among them. Not one proved effectiveness.¹²

Why Lab Results Did Not Translate to Humans

One reason the laetrile story persists is that amygdalin does show activity against cancer cells in laboratory dishes. Researchers have reported that it can trigger programmed cell death and slow the growth and spread of various cancer cell types in vitro.¹³ This is often cited in online forums and on supplement-selling websites as evidence that amygdalin “works.”

The problem is that killing cancer cells in a petri dish is a very low bar. Bleach kills cancer cells in a dish. So does ethanol. The critical question is whether a compound can be delivered at effective concentrations inside a living human body, targeting cancer tissue selectively without poisoning the rest of the patient. On that front, there is no convincing evidence that amygdalin causes tumor regression in humans, especially in people with advanced disease. At the same time, some researchers have noted that when purified amygdalin is given intravenously in controlled doses rather than orally, overt toxicity is less pronounced, though the absence of toxicity is not the same as the presence of benefit. The overall picture is that multiple aspects of amygdalin’s potential have not been adequately explored, but nothing tested so far in humans has worked.

Some recent research has explored loading amygdalin into nanoparticles, hoping to increase its concentration at tumor sites while limiting cyanide exposure elsewhere. This work is entirely preliminary and confined to the lab. No nanoparticle formulation of amygdalin has been tested in humans.¹⁴

Real Poisoning Cases

The medical literature contains numerous case reports of people poisoned by apricot kernels or amygdalin supplements. These are not theoretical risks. In one case, a 41-year-old woman purchased apricot kernels from a health food store, ate them, and within 20 minutes became weak and short of breath. By the time she reached the hospital she was comatose and hypothermic. She responded to antidotal therapy for cyanide poisoning but required a continuous thiosulfate infusion for persistent metabolic acidosis.¹⁵

In another case, a 35-year-old woman consumed more than 20 apricot kernels. Published literature estimated each kernel contained cyanide concentrations averaging around 2.9 milligrams per gram. She initially appeared fine but about 70 minutes later developed headache, nausea, difficulty breathing, low blood pressure, and dangerously low oxygen levels. She was treated with hydroxocobalamin, a cyanide antidote.¹⁶

Chronic exposure is also documented. One patient had been taking apricot kernel extract daily for five years as a self-prescribed remedy. The ongoing low-level cyanide exposure affected peripheral oxygen readings, causing a pulse oximeter to give falsely low results during surgery. Once the patient stopped taking the extract, oxygen measurements returned to normal.¹⁷ That case is a useful reminder that the dangers are not limited to a single dramatic overdose; sustained low-dose exposure can quietly cause harm.

How Apricot Kernels End Up on Store Shelves

Despite the evidence, you can still buy raw apricot kernels and amygdalin supplements online and in some health food stores. This is partly a regulatory gap. In the United States, the FDA banned laetrile as an injectable drug in the 1970s, but raw apricot kernels are sold as food products, not drugs, so they sidestep that ban. Supplement manufacturers avoid making explicit cancer treatment claims on labels while relying on internet marketing, word of mouth, and books from the alternative-medicine ecosystem to drive sales. In Europe and Australia, regulators have set limits on amygdalin content in food products, and some countries have banned the sale of bitter apricot kernels outright. But enforcement is inconsistent, and products still circulate freely on global e-commerce platforms.

The “B17” label itself is part of this marketing architecture. Calling something a vitamin implies it is a natural substance your body needs and that mainstream medicine is overlooking. That framing taps into a deep vein of distrust toward conventional oncology. For someone facing a cancer diagnosis, the narrative that a simple natural compound could help, but is being suppressed by pharmaceutical interests, can be powerfully appealing. Understanding that amygdalin is not a vitamin, that no deficiency disease corresponds to it, and that its “vitamin” status was invented by its promoter is essential context for evaluating those claims.

Cyanogenic Glycosides Beyond Apricot Kernels

Amygdalin is just one member of the larger cyanogenic glycoside family. These compounds show up across the plant kingdom, and humans have encountered them throughout history. Cassava, a dietary staple for hundreds of millions of people in sub-Saharan Africa and parts of South America and Asia, contains a different cyanogenic glycoside called linamarin. When cassava is properly processed through soaking, fermenting, and drying, the cyanogenic compounds are broken down and the food is safe. When processing is insufficient, chronic cyanide exposure results. This has been linked to konzo, a distinct paralytic neurological disease seen in communities that depend heavily on improperly processed cassava, especially during famine conditions when nutritional status is already poor.¹⁸

The konzo story is instructive because it illustrates the spectrum of cyanogenic glycoside risk. At one end, you have incidental exposure from common foods like apple seeds or lima beans, well within the body’s detoxification capacity and essentially harmless. At the other end, you have intentional consumption of concentrated amygdalin supplements or chronic reliance on poorly prepared cyanogenic staples, both of which overwhelm the rhodanese system and cause real damage. The dose, the route, and the nutritional background of the person all matter enormously. This is why blanket statements like “amygdalin is natural and safe” or “apricot kernels are deadly poison” both miss the mark. The compound is genuinely dangerous when consumed in the quantities promoted by laetrile advocates, and genuinely inconsequential in the trace amounts present in ordinary fruit consumption.

What Would Legitimate Research Look Like

Some researchers continue to investigate whether any therapeutic use can be salvaged from amygdalin. The focus has shifted away from the old laetrile model, where patients swallowed pills or received crude extracts, toward two newer approaches. One involves nanoparticle delivery systems designed to concentrate amygdalin at tumor sites and limit systemic cyanide release.¹⁹ The other investigates the compound’s interactions with gut bacteria, since microbial composition appears to influence how much cyanide is generated from a given dose of amygdalin.²⁰

Both lines of work are at the earliest stages of preclinical investigation. None of the nanoparticle formulations have entered human trials, and the gut-microbiome angle has not produced a practical therapeutic strategy. If amygdalin ever proves useful in medicine, it will likely be as a heavily engineered pharmaceutical, not as ground-up apricot pits from a health food store. The gap between a promising molecule and a working drug is vast, and amygdalin has not crossed it in over half a century of attention.

Buying Apricot Kernels Safely

If you eat stone fruit, you may occasionally encounter the kernel inside the pit. Swallowing an intact kernel whole, without chewing, limits enzyme exposure and reduces cyanide release. Eating one or two kernels, even chewed, is unlikely to cause harm in a healthy adult, though individual variation in gut flora means no universally safe number exists. The danger arises with quantities in the range of 20 or more raw bitter kernels eaten at once, or with sustained daily consumption of kernel extracts over weeks and months.

Sweet apricot kernels, the type commonly sold as snacks in Mediterranean and Middle Eastern cuisine, contain far less amygdalin than bitter kernels and are generally considered safe in normal dietary amounts. Bitter kernels, which have a sharply astringent taste, contain the highest concentrations. If a kernel tastes intensely bitter, that bitterness is the amygdalin, and it is a signal to stop eating. The European Food Safety Authority has recommended that adults consume no more than three small apricot kernels per sitting, a conservative threshold based on estimated cyanide release. Children should eat none.

For anyone currently taking amygdalin or apricot kernel supplements as a cancer treatment or general health measure, the evidence points clearly in one direction. No clinical benefit has been demonstrated in any controlled study, and the risk of cyanide poisoning, whether acute or chronic, is well documented. Discussing any supplement use with a physician, especially one that releases cyanide as its primary metabolic byproduct, is not overcautious. It is the minimum reasonable step.