Does Laetrile (Vitamin B17) Cure Cancer?

Often it is a bag of bitter apricot seeds; sometimes it is a bottle labeled "vitamin B17." A simple substance from fruit pits kills cancer cells and spares healthy ones, the pitch goes, and drug companies buried it because nobody can patent a seed. All you have to do is take it.

It is a good story, almost every part of it is wrong, and some of the wrong parts can hurt you.

Amygdalin is a real compound. NCI says it is found in fruit pits, such as apricot pits, and in raw nuts, lima beans, clover and sorghum. Laetrile is another name for amygdalin. NCI's detailed summary adds that the names are often used as if they mean the same thing, but they are not the same product. The patented U.S. Laetrile is a semisynthetic form of amygdalin. The Mexican product is made from crushed apricot pits.

The name "vitamin B17" was given to laetrile by E.T. Krebs Jr. The committee that approves vitamin names, part of the American Institute of Nutrition, never approved it. NCI is blunt about this. There is no evidence that laetrile is needed for normal metabolism, or that it can work as a vitamin in animals or people.

A vitamin sounds both safe and necessary. A cyanide-releasing plant compound does not. The label did a lot of work.

When amygdalin breaks down it releases hydrogen cyanide. This is ordinary chemistry, not rhetoric. NCI says the breakdown also makes benzaldehyde and glucose.

Supporters offered theories for why this might kill tumors. One idea was that cancer cells hold more of certain enzymes and less rhodanese, the enzyme that turns cyanide into a far less harmful compound. NCI says some lab findings fit parts of these ideas. But the animal and human studies, described below, found no anticancer benefit.

How you take it changes the danger. NCI says cyanide poisoning is much more common when laetrile is swallowed. Gut bacteria and some plants in food carry enzymes that release the cyanide. Little breakdown happens when laetrile is injected. In one rat study, germ-free rats had no side effects and normal blood cyanide. Rats with normal gut bacteria showed signs of cyanide poisoning, such as lethargy and convulsions.

Some everyday foods make it worse. NCI says side effects get worse with raw almonds or crushed fruit pits, with certain fruits and vegetables (it names celery, peaches, bean sprouts and carrots), and with high doses of vitamin C. In an early NCI study, two patients who ate raw almonds while taking laetrile by mouth developed signs of cyanide poisoning.

The reported harms are not minor. NCI's list runs from nausea, vomiting, headache and dizziness, through a blue color of the skin, liver damage, very low blood pressure, a droopy upper eyelid and nerve damage that makes walking difficult. It also includes fever, confusion, coma, and death.

This is the part the suppression story leaves out. Laetrile was not ignored. It was studied with public money by NCI.

NCI sponsored animal studies in rats and mice with several kinds of cancer. None of the solid tumors or leukemias responded at any dose tested, and survival did not improve in any treated group.

NCI then asked practitioners for case reports from people who believed laetrile helped. Of 93 submitted, 67 could be evaluated. An expert panel found two complete responses and four partial responses. That was thin, but it was not nothing. On the basis of those six responses, NCI agreed to sponsor human trials.

Charles Moertel and colleagues published the main trial in 1982. It used the routine laetrile practitioners followed. Patients got amygdalin by vein for 21 days, then pills, plus vitamins, pancreatic enzymes, and a set diet. There were 175 patients who could be evaluated, most with breast, colon, or lung cancer.

Only one patient met the criteria for a response. It was a partial response, and it lasted 10 weeks. By the end of the intravenous course, 54 percent of patients had measurable disease progression. Seven months after the intravenous course ended, every patient's disease had progressed. About 20 percent claimed some relief of symptoms, and 7 percent reported better ability to work or do routine activities at some point. In most patients, these benefits did not last. Blood cyanide levels were not raised after the intravenous treatment, but they were raised after the pills.

That is not a buried result. That is a result.

NCI says the FDA has not approved laetrile for cancer or any other condition. An application to study it as a new drug was filed in 1970. It was first approved, then rejected. NCI says the reasons were that animal studies showed laetrile was not likely to work, and that there were questions about how the study would be run. Court fights followed, and more than 20 states legalized it in the 1970s. In 1980 the U.S. Supreme Court upheld a federal ban on shipping it between states.

It never went away. NCI says it is still made and used, mostly in Mexico and in some U.S. clinics. The FDA does not regulate how it is made, so batches can vary in purity and contents. Labels have been found to be wrong, and samples have been found contaminated with bacteria and other substances. You do not really know your dose, which matters enormously for something that releases a poison.

The FDA still acts against sellers. In 2021 it sent a warning letter to a company selling bitter apricot seeds, amygdalin extract and a product called Laetrile B17. The letter quoted website claims that B17 is "killing harmful cells" and that it "works in the control of cancer."

Because the appeal is real, and it is not foolish.

Cancer strips away control, and laetrile hands some back. You can buy it online without anyone's permission. The story even explains why your doctor says no, which converts that "no" into proof rather than a warning. And it usually arrives from someone who is frightened for you and desperate to do something useful. That is not a bad motive.

Testimonials feel like evidence because they are about actual people. But a story cannot separate the remedy from everything else going on. People who take laetrile may also be having surgery, chemotherapy, or radiation. Some cancers move slowly. Trials exist precisely because a story cannot sort that out.

Cyanide poisoning is the obvious risk. Another risk is time. NCI says laetrile has been studied and found not to work. Time spent on apricot seeds is time not spent on a treatment that might. This harm is silent. Nobody feels it happening, and it shows up later, on a scan.

You can say that to a relative without starting a fight. Begin with "I know you are trying to help," then hand them something real to do — a ride, a meal, a seat beside you during infusion.

Three questions do most of the work.

Was it ever actually tested? Search the name plus "PDQ" at cancer.gov, where NCI keeps summaries on alternative cancer treatments, including the ones that failed.

Does the cover-up story survive a look at the dates? Laetrile's own history breaks it, because NCI, part of the same federal government, sponsored the trials.

Who profits? FDA warning letters are public, so search the product name at fda.gov. The sentences quoted back at a company are often the exact ones that first convinced you.

If you are already taking it, tell your oncology team. NCI says some alternative therapies can affect standard treatment or cause harm when used with it.

• Call 911 or go to the nearest emergency department if someone who has taken laetrile is suddenly confused, is hard to wake, or has skin that looks blue.
• Call Poison Help at 1-800-222-1222 if someone has swallowed laetrile, amygdalin pills or apricot seeds and you are worried.
• Call your care team right away if you have taken laetrile and develop nausea, vomiting, headache, dizziness, or trouble walking.

• Laetrile/Amygdalin (PDQ) Health Professional Version — National Cancer Institute
• Laetrile/Amygdalin (PDQ) Patient Version — National Cancer Institute
• Illegally Sold Cancer Treatments — US Food and Drug Administration
• Warning Letter: Richardson Nutritional Center — US Food and Drug Administration
• Poisoning — MedlinePlus