Amygdalin/Laetrile

Description and background    

The terms amygdalin, laetrile and “vitamin B17” are often used synonymously but refer to different products.

Amygdalin is a secondary plant compound belonging to the group of cyanogenic glycosides characterized by the release of cyanide upon enzymatic degradation. Amygdalin is also known as mandelonitrile-beta-glucuronide (semi-synthetic), mandelonitrile beta-D-gentiobioside (natural product), amygdalina, and nitriloside.

Laetrile is an acronym derived from ‘LAEvorotatory’ and ‘mandeloniTRILE’ and is used to describe a purified, semi-synthetic form of amygdalin.

Although not a vitamin, amygdalin is sometimes also referred to as “vitamin B17”, a name given to it by chemist E.T. Krebs. According to a historical theory cancer develops as a result of deficiency of "vitamin B17" (Milazzo 2015).

Amygdalin was first identified and isolated by French chemists in 1830 and was used as an anti-cancer agent in 1845 in Russia. By the 1920s amygdalin had reached the US, but the early pill form was considered to be too toxic and its use was discontinued. In the 1950s an apparently non-toxic, semi--synthetic intravenous form of amygdalin was developed by Ernst T Krebs in the U.S., and this became known as laetrile.

In the 1970s laetrile gained popularity either as a single-agent treatment or as part of a metabolic treatment regimen that also included high-dose vitamin supplements and enzymes (Chandler 1984). The popularity of laetrile reached its peak in the United States in 1978 when it was reported that 70,000 people had been treated with it (Chandler 1984). Current prevalence data are not available.

Ingredients and quality issues

Amygdalin is a secondary plant compound belonging to the group of cyanogenic glycosides, which are enzymatically degraded by beta-glucosidases to form cyanide. The compound is found in the seeds of apricots, peaches and bitter almonds and also in plants such as lima beans, clover and sorghum.  Minor amounts of amygdalin may be ingested when eating a balanced diet.

The chemistry of laetrile available in the United States is different from the one used in Mexico. The laetrile used in Mexico may be crushed apricot seeds rather than the semi-synthetic form of laetrile (mandelonitrile-beta-glucuronide) that is used in the US (Davignon 1978). Therefore it is conceivable that not all studies on laetrile have looked at the same compound.

Application and dosage

Amygdalin is usually taken orally in the form of bitter apricot seeds. Laetrile is available for oral administration as well as intravenous or intramuscular injection. Treatment is typically initiated intravenously for two to three weeks and then continued orally. Laetrile is also used as an enema form or applied directly to skin lesions.

Alleged indications

Suppliers have postulated the use of amygdalin/laetrile as anti-cancer treatment. Many supporters of laetrile refer to anthropological evidence from epidemiological studies of secluded cultures consuming high levels of foods rich in amygdalin, e.g.  the Hunzakots of Pakistan, the Inuit of the Arctic or the indigenous Hopi and Navajo of North America (McCarrison 1936).

Expeditions have reported extraordinary longevity and the absence of cancer in these cultures, however the studies are often flawed due to language barriers, highly selected contacts and sometimes deliberate misinformation. They fail to provide clear evidence for a causal relationship between the uptake of amygdalin and the incidence of cancer.

Mechanisms of action

It has been claimed that amygdalin could exert its anticancer activity via inducing apoptosis, inhibiting tumour cell growth, and reducing tumour cell metastasis (He 2020).

Proponents ascribe the anticancer effects to the cyanide released upon enzymatic degradation of the compound. They postulate that amygdalin is selectively effective against cancer cells only. This hypothesis involves an imbalance of the enzymes beta-glucosidases, beta-glucuronidase and rhodanase in cancer cells as compared to healthy cells.

Malignant cells are claimed to be specifically vulnerable to cyanogenic glycosides because of two characteristics: firstly, a higher level of beta-glucosidases and beta-glucuronidase compared to healthy cells, which would lead to a more rapid intracellular release of cyanide from laetrile or amygdalin, and secondly, a deficiency in rhodanase, an enzyme that converts cyanide into the harmless compound thiocyanate (Ellison 1978, BfArM 2014, He 2020).

Legal issues

In the US laetrile has had a long controversial history. This includes inaccurate theories of how it works, conspiracy theories of unpublished research studies supporting its use, banning of its use in the US by the Food and Drug Administration (FDA), and prison sentences for many proponents and suppliers (including ET Krebs himself). The controversy continues.

In the United Kingdom the Medicines and Healthcare Products Regulatory Agency (MHRA) has assigned amygdalin/laetrile /B17 the status of a prescription-only medicine. The substance is not banned but it is unlicensed, and so access to it is subject to prescription by a medical doctor. This implies that doctors can supply it to a patient should they consider it an appropriate treatment, but do so at their own risk. There is no licensed product containing the substance laetrile/amygdalin/B17 in the UK.

Drugs containing amygdalin are not approved by the regulatory authorities in Germany and are considered unsafe according to the German Drug Act.