Common Names
- Apricot pits
- vitamin B17
- mandelonitrile-beta-glucuronide (semi-synthetic)
- mandelonitrile beta-D-gentiobioside (natural product)
- laevorotatory and mandelonitrile
- prunasin
For Patients & Caregivers
Amygdalin (Laetrile) has toxic side effects and decreased survival in cancer patients.
Amygdalin (also called Laetrile®) is an extract derived from apricot pits and other plants. It can be broken down by enzymes in the intestine to produce cyanide, a known poison. It was first used in Europe and later in the United States as an alternative cancer therapy. Promoters claimed that the cyanide released from amygdalin selectively killed cancer cells, leaving normal tissue cells unharmed. When fed to laboratory animals that had cancer cells implanted in them, amygdalin did not reduce the tumor size or slow their growth. In a clinical study, cancer patients using amygdalin did not have any benefits but some showed cyanide toxicity.
There is renewed interest in studying amygdalin after the discovery of new anticancer mechanisms. However, cancer patients should not use this product in the current form until more is known about its safety and effectiveness.
- Amygdalin is not an approved drug in the United States.
- Laboratory analysis showed that some samples of amygdalin have been contaminated with microbes and substances that induce fever. This analysis also showed that both the injectable and oral forms contained less active product than was claimed on the label.
The Food and Drug Administration has banned the sale and use of amygdalin (Laetrile®) due to the risk of cyanide poisoning. For this reason, Laetrile® is only offered at alternative medicine clinics outside the United States. Some clinics use it as a component of multi-modality metabolic therapies. Such therapies generally have not been found effective and are discussed at greater length in a separate monograph about metabolic therapies.
For Healthcare Professionals
Amygdalin is a naturally occurring cyanogenic glycoside derived from nuts, plants, and the pits of certain fruits, primarily apricots. Bitter almonds containing amygdalin are used in Traditional Chinese Medicine to remove “blood stasis” and to treat abscesses (1). Amygdalin was first used to treat cancer more than a century ago in Russia and later in the United States. A purified form sold as Laetrile has been a popular alternative cancer therapy since the 1960s. Some claimed amygdalin to be a vitamin (B17) and that deficiencies could cause cancer, but this is not substantiated by scientific evidence (2). Amygdalin is banned in the United States but it is available in other countries and online.
Amygdalin is metabolized by the enzyme beta-glucosidase into benzaldehyde, glucose and cyanide in the intestine (3) (4). Cyanide from the hydrolysis of amygdalin is believed to be cytotoxic with actions selective against cancerous cells, but results from animal studies were mostly negative (4) (5) (6). Other animal studies suggest it may help to relieve pain due to its anti-inflammatory (7) and analgesic effects (8).
One study suggested amygdalin can inhibit tumor growth, but subsequent tests were unable to confirm this observation (9). A clinical trial in the late 1970s supported by the National Cancer Institute did not find amygdalin to be beneficial, and some patients in the study developed cyanide toxicity (10). A systematic review also concluded that amygdalin is ineffective against cancer (11).
With the recent discovery of anticancer properties of amygdalin through previously unknown mechanisms (12) (13) (14) (15) (16) (32), there is renewed interest in whether this agent may have potential as an anticancer treatment.
Amygdalin has severe adverse effects. It should not be used as a therapy in the current form.
Amygdalin is metabolized by the enzyme beta-glucosidase, which removes the glucose molecules to form prunasin and mandelonitrile. This is further broken down to benzaldehyde and hydrocyanic acid (3) (4). When consumed orally, amygdalin is more likely to produce cyanide toxicity, as compared with the injectable form (17), possibly due to the presence of enzymes from the microflora in the intestine (18). Cyanide from the hydrolysis of amygdalin is cytotoxic. It was postulated that this action is selective against cancerous cells because normal cells convert the cyanide to benign thiocyanate via rhodanese (19) (20) (21). This theory has not been proven in humans (22).
Amygdalin demonstrated anti-inflammatory effects by promoting the immunomodulating function of Treg cells (24). In animal studies, amygdalin suppressed prostaglandin E(2) synthesis and nitric oxide production through COX-2 and iNOS inhibition (7). It reduced inflammation pain by inhibiting tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1beta) (8).
Amygdalin exerts neurotrophic effects by activating the extracellular-signal-regulated kinase (ERK) 1/2 pathway (25).
Recent studies found amygdalin may have anticancer effects. In animals, amygdalin inhibits the tumor-promoting effect of the Epstein-Barr virus (12). In human prostate cancer DU145 and LNCaP cells, amygdalin increased pro-apoptotic Bax protein expression and caspase-3 enzyme activity, while decreasing anti-apoptotic Bcl-2 protein expression (23). It downregulates cell cycle-related genes in SNU-C4 human colon cancer cells (13). An in vitro study suggests amygdalin may inhibit growth and proliferation in bladder cancer cell lines by decreasing cell cycle regulatory proteins cdk2 and cyclin A (16). It also induces growth-regulating protein follistatin expression in human hepatocarcinoma HepG2 cells (15).
Case reports
Oral: Dermatitis and cyanide toxicity including nausea, vomiting, headache, dizziness, mental obtundation, cyanosis, hypotension, ptosis, neuropathies, coma, and death (10) (17) (29) (27) (30).
Oral: Severe cyanide poisoning following ingestion of 3 grams of amygdalin with concurrent use of high doses of vitamin C (26).
Oral: Consumption of amygdalin caused peripheral neuropathy in a patient with vitamin B12 deficiency (31).
Oral and Intraveous: Administration of intravenous and oral amygdalin caused cyanide poisoning characterized by serious agitaion and encephalopathy in a 4-year-old (33).
Oral: Hypoxia from cyanide toxicity after consumption of apricot kernel extract (34).