Laetrile

Other common name(s): amygdalin, vitamin B17, Amigdalina B-17

Scientific/medical name(s): mandelonitrile beta-D-gentiobioside, mandelonitrile-beta-glucuronide

Description

Laetrile is a chemically modified form of amygdalin, a naturally-occurring substance found mainly in the kernels of apricots, peaches, and almonds. However, the terms amygdalin and Laetrile are often used interchangeably. The name Laetrile is also used to describe a closely related, man-made substance. Laetrile and amygdalin are promoted as alternative cancer treatments.

Overview

Available scientific evidence does not support claims that Laetrile or amygdalin are are effective in treating cancer or any other disease. Both contain a small amount of a substance that can be converted to cyanide in the body, and several cases of cyanide poisoning have been linked to the use of Laetrile. The U.S. Food and Drug Administration (FDA) has not approved Laetrile as a medical treatment in the United States.

How is it promoted for use?

Supporters once called Laetrile "the perfect chemotherapeutic agent," as it was said to kill cancer cells while being non-toxic to normal cells. Promoters claim that societies with diets rich in amygdalin, such as the Hunza and the Karakorum, are "cancer-free peoples." Supporters also say that Laetrile can prevent cancer and can help patients stay in remission. It is also promoted to provide pain relief to people with cancer. Other reported uses for Laetrile have been in the prevention and treatment of high blood pressure and arthritis.

There are several proposed explanations for how Laetrile works. Supporters claim that cancer cells contain more of a certain enzyme that splits the Laetrile molecule and releases the cyanide within it. The cancer cell then supposedly dies from cyanide poisoning. Normal cells supposedly do not have as much of this enzyme and instead contain an enzyme that renders the Laetrile harmless. Supporters claim that normal cells are not affected for this reason.

Another popular theory is that cancer is really a "vitamin deficiency" and that Laetrile is the missing "vitamin B17." Laetrile does not meet the widely accepted scientific definition of a vitamin, in that it has not been proven to be essential to achieving or maintaining good health.

What does it involve?

Amygdalin is most commonly extracted from apricot pits. Laetrile is a related substance, which has a slightly different chemical structure. Laetrile or amygdalin are often taken as part of a metabolic therapy that includes a specific diet with high doses of vitamins (see Metabolic Therapy). Although no standard treatment plan exists, a typical treatment consists of injecting Laetrile or amygdalin into a vein each day for 2 to 3 weeks, followed by taking tablets by mouth as a maintenance therapy. Laetrile and amygdalin are also used in enemas and in solutions applied directly to skin lesions. Chemical analyses of products sold as Laetrile showed that the actual ingredient is often amygdalin rather than Laetrile. For this reason, and because the terms are often used as synonyms, both substances are called Laetrile in the remainder of this document unless otherwise noted.

Laetrile treatments may cost thousands of dollars per week. Laetrile is commonly used in some hospitals and clinics in northern Mexico because it is difficult to get in the United States.

What is the history behind it?

"Bitter almonds" have been used as a medical remedy for thousands of years by cultures as diverse as the ancient Egyptians, Chinese, and Pueblo Indians. In 1802, a chemist discovered that distilling the water from bitter almonds released hydrocyanic acid. In the 1830s, the source of this hydrocyanic acid was purified and called amygdalin. It was thought to be the active ingredient in bitter almonds.

According to a 1991 review, the current use of Laetrile can be directly attributed to the theories of Ernst T. Krebs, Sr., MD, which were first proposed in the 1920s. Krebs tested an extract from apricot pits to treat cancer, but the pills proved too toxic for human use.

Around 1952, his son, Ernst T. Krebs, Jr., changed the process of extracting amygdalin and created a chemically modified version, which he named Laetrile. He claimed that the new substance was more potent as an anti-cancer drug than naturally occurring amygdalin. Despite this chemical distinction, both proponents and skeptics commonly refer to both substances as Laetrile. Adding to this confusion is the fact that many products sold as Laetrile consist mostly of amygdalin.

The same 1991 review notes that, beginning in 1957, Laetrile was repeatedly tested against tumor cells implanted in animals. At least a dozen separate sets of experiments were done at seven institutions. Targets included several different types of cancer. The conclusion was that Laetrile did not have any anti-tumor activity.

The FDA placed sanctions against the sale of Laetrile. In 1977, the FDA commissioner stated that there was no evidence for the safety or effectiveness of Laetrile. Because of the risk of cyanide poisoning, the government has banned the transport of Laetrile into the United States or across state lines, as well as the use of Laetrile in states without laws specifically allowing it. Since 2000, there have been several instances of prosecution because of Laetrile transport across state lines.

What is the evidence?

From the 1950s through the 1970s, Laetrile grew in popularity in the United States as an alternative treatment for cancer. For this reason, and despite the lack of scientific evidence that Laetrile was effective, the National Cancer Institute (NCI) studied it in 1978 through a retrospective case review (a study that looks back at cases from the past). The NCI sent letters to more than 400,000 doctors and other practitioners, asking them to submit positive results from cases involving Laetrile. While an estimated 75,000 people in the United States had taken Laetrile, only 93 "positive" cases were submitted, and in only 6 of those was there evidence of major tumor shrinkage.

A 1991 NCI review of the evidence of Laetrile’s effectiveness stated that "scientific studies were conducted for more than 20 years, starting in the mid-1950s, looking for evidence of antitumor efficacy by Laetrile. In no instance was evidence found that treatment with Laetrile results in any benefit against tumors in animals. Despite this negative record, a clinical trial in humans was conducted in 1981. It did not show any anticancer effect of Laetrile."

The clinical trial of Laetrile on humans was performed between 1979 and 1981 at medical centers around the country. About 175 patients with different types of cancer were treated with a commonly used regimen of Laetrile plus metabolic therapy (see Metabolic Therapy). Published in 1982, it reported that one patient had major tumor shrinkage (a partial response) at first. Of the patients, 91% of their cancers had progressed after 3 months, and median survival was less than 5 months. In all patients, their cancer grew within 8 months of starting treatment.

In contrast to the findings the NCIs findings, one of the leading proponents of Laetrile claims to have treated nearly 30,000 cancer patients in several studies of the drug with promising results. However, these results have not been reviewed or repeated by the scientific medical community.

The consensus of available scientific evidence does not support claims that Laetrile is an effective anti-cancer treatment, either in animal studies or in human clinical trials. Cancer cells do not seem to be more susceptible to the effects of Laetrile than normal cells. The successes claimed by its supporters are based on individual reports, testimonials, and publicity issued by promoters.

Are there any possible problems or complications?

The use of Laetrile has been linked to cyanide toxicity and death in a few cases. Although drug interactions are unknown, at least one case report suggests that vitamin C may increase the amount of cyanide released from Laetrile in the body. This can increase the risk of cyanide poisoning. This risk is also likely to be increased if the person also eats raw almonds or crushed fruit pits while taking Laetrile. Eating fruits and vegetables that contain beta-glucosidase (such as celery, peaches, bean sprouts, and carrots) may increase the risk of cyanide poisoning. Always tell your doctor and pharmacist about any supplements or herbs you are taking.

This treatment should be avoided by children, and by women who are pregnant or breast-feeding. Relying on this type of treatment alone, and avoiding or delaying conventional medical care for cancer, may have serious health consequences.

Additional resources

More information from your American Cancer Society

The following information on complementary and alternative therapies may also be helpful to you. These materials may be found on our Web site (www.cancer.org) or ordered from our toll-free number (1-800-ACS-2345).

Guidelines for Using Complementary and Alternative Therapies

Dietary Supplements: How to Know What Is Safe

The ACS Operational Statement on Complementary and Alternative Methods of Cancer Management

Complementary and Alternative Methods for Cancer Management

Placebo Effect

Learning About New Ways to Treat Cancer

Learning About New Ways to Prevent Cancer

References

American Cancer Society. Unproven methods of cancer management. Laetrile. CA Cancer J Clin. 1991;41:187-192.

Bromley J, Hughes BG, Leong DC, Buckley NA. Life-threatening interaction between complementary medicines: cyanide toxicity following ingestion of amygdalin and vitamin C. Ann Pharmacother. 2005;39:1566-1569.

Ellison NM, Byar DP, Newell GR. Special report on Laetrile: the NCI Laetrile review. Results of the National Cancer Institute’s retrospective Laetrile analysis. N Engl J Med. 1978;299:549-552.

Fetrow CW, Avila JR. Professional’s Handbook of Complementary and Alternative Medicines. Springhouse, Pa: Springhouse Corp; 1999.

Herbert V. Laetrile: The Cult of Cyanide: Promoting Poison for Profit. Am J Clin Nutr. 1979;32:1121-1158.

Lerner IJ. Laetrile: a lesson in cancer quackery. CA Cancer J Clin 1981;31:91-95.

Memorial Sloan-Kettering Cancer Center. About herbs: Amygdalin. 2006. Accessed at: www.mskcc.org/mskcc/html/69118.cfm on June 11, 2008.

Milazzo S, Lejeune S, Ernst E. Laetrile for cancer: a systematic review of the clinical evidence. Support Care Cancer. 2006.

Moertel CG, Fleming TR, Rubin J, et al. A clinical trial of amygdalin (Laetrile) in the treatment of human cancer. N Engl J Med. 1982;306:201-206.

National Cancer Institute Physician Data Query (PDQ). Laetrile/Amygdalin. 2006. Accessed at: www.cancer.gov/cancertopics/pdq/cam/laetrile/healthprofessional on June 11, 2008.

Wilson B. The rise and fall of laetrile. 2004. Accessed at: www.quackwatch.org/01QuackeryRelatedTopics/Cancer/laetrile.html on June 11, 2008.

Note: This information may not cover all possible claims, uses, actions, precautions, side effects or interactions. It is not intended as medical advice, and should not be relied upon as a substitute for consultation with your doctor, who is familiar with your medical situation.