1. Introduction: A Cyanide-Releasing Compound Marketed as a Cure
Amygdalin is a naturally occurring compound found in the kernels of bitter almonds, apricots, and other stone fruits. Its semi-synthetic form, called laetrile (and marketed as «vitamin B17,» though it is not a vitamin). It was promoted from the 1950s onward by Ernst Krebs and others as a «selective» cancer cure that would release cyanide only inside tumor cells. Regulatory agencies banned it after controlled trials showed no benefit, and it is associated with documented cases of cyanide poisoning. It is a textbook example of a disproven alternative cancer «cure» that persists in marketing despite clear evidence of harm.
2. Chemistry and the «Selectivity» Claim
Amygdalin is a cyanogenic glycoside: it contains a sugar moiety bound to a cyanide-containing structure. When it is broken down by the enzyme β-glucosidase, it releases hydrogen cyanide, a potent cellular poison that blocks mitochondrial respiration. The central claim of the laetrile proponents was that cancer tissue contains higher levels of β-glucosidase and lower levels of the protective enzyme rhodanese, so that cyanide would be released preferentially in tumors. This alleged differential was not confirmed. In reality, oral amygdalin is metabolized largely by gut bacteria, and the release of cyanide is neither tumor-specific nor controllable — it can poison normal tissues, including the liver, and the biologically available cyanide is not directed to cancer.
3. Evidence From Controlled Trials
The definitive test came in a trial sponsored by the US National Cancer Institute and reported by Moertel and colleagues in 1982: patients with various advanced cancers were treated with amygdalin (laetrile) using the protocol advocated by its proponents. No patient had a complete or partial response, and some developed symptoms of cyanide toxicity. A second controlled study of laetrile plus a «metabolic» regimen similarly found no benefit. Subsequent reviews have consistently concluded that amygdalin has no established anticancer activity. The rigorous trials therefore refuted the original anecdotal claims.
4. Documented Harm: Cyanide Poisoning
- Acute cyanide toxicity. Case reports and poison-center data document serious and sometimes fatal cyanide poisoning after ingestion of amygdalin or apricot kernels, including in children.
- Chronic toxicity. Repeated exposure can cause neurological injury and thyroid effects, among other problems.
- Increased risk with gut β-glucosidase. Because gut bacteria can hydrolyze amygdalin to release cyanide, oral consumption is the most hazardous route; co-administration of «enzyme» products can worsen it.
- Delay of effective treatment. As with other alternative cancer «cures,» the most common serious harm is the loss of a window in which conventional treatment could have been effective.
5. Regulatory Status
Laetrile and amygdalin are not approved as cancer treatments by the US Food and Drug Administration or equivalent agencies, and their importation for use as a drug is illegal in many countries. The «vitamin B17» label is a marketing construction: amygdalin is not a vitamin, and deficiency of it does not cause disease. Health agencies have repeatedly warned the public against amygdalin and apricot-kernel «cures.»
6. Why the Claim Persists
Despite being disproven decades ago, amygdalin retains a following. Reasons include the enduring appeal of a «natural» cure, distrust of conventional medicine, the emotional weight of a cancer diagnosis, and the persistence of anecdotal success stories that cannot withstand controlled scrutiny. The selectivity hypothesis, though false, is intuitive enough to be repeated uncritically. Understanding these dynamics helps clinicians respond to patients with empathy rather than dismissal, while being unequivocal that amygdalin does not treat cancer and can cause poisoning.
7. Unresolved Questions and Speculative Directions
- If the selectivity claim is false and toxicity is unpredictable, there is no sound basis for further clinical development of amygdalin as a cancer drug. [Marked for verification.]
- Targeted delivery of cyanogenic compounds with tumor specificity is a theoretical concept, but no such product exists and it is unrelated to laetrile.
8. Conclusion
Amygdalin (laetrile, «vitamin B17») does not treat cancer. Controlled trials showed no response, and its consumption can cause potentially fatal cyanide poisoning, especially via oral apricot kernels. Its selectivity rationale was never confirmed, and it is banned or restricted by regulators. It should not be used as a cancer treatment, and doing so risks both poisoning and the loss of effective conventional care.
Sources and Key Research Centers
- National Cancer Institute — PDQ summary on laetrile/amygdalin.
- US Food and Drug Administration — warnings on laetrile and fraudulent cancer cures.
- Cyanide poisoning from apricot kernels — poison-center case series and reports. [Citation details to be verified.]
- Controlled trial of amygdalin
- Moertel CG, Fleming TR, Rubin J, et al. «A clinical trial of amygdalin (Laetrile) in the treatment of human cancer.» New England Journal of Medicine, 1982; 306(4): 201–206. [Citation details to be verified.]
- Second controlled trial of laetrile plus metabolic therapy — Moertel CG et al., New England Journal of Medicine, 1982. [Citation details to be verified.]
Note: citation identifiers are provided where available; readers should confirm bibliographic details against the publisher’s record. This article is an editorial scientific overview and is not a medical recommendation.