Does apricot-kernel extract (laetrile / 'vitamin B17') treat cancer?

The short answer

No. Laetrile does not treat cancer.

It was tested in a clinical trial sponsored by the National Cancer Institute. The trial enrolled 178 patients in the late 1970s and early 1980s. The published conclusion was blunt: "Amygdalin (Laetrile) is a toxic drug that is not effective as a cancer treatment."

The FDA has never approved it for cancer, or for anything else.

The rest of this page explains what it is and what the trial found.

What laetrile is

Amygdalin is a natural compound. It is found in the pits of apricots and other stone fruit, and in raw nuts, lima beans, clover, and sorghum.

In the 1950s an injectable form was patented in the United States as Laetrile. In the 1970s it was promoted hard as an alternative cancer treatment. By 1978, more than 70,000 Americans were reported to have used it.

The names are used loosely. The US-patented Laetrile and the amygdalin made in Mexico from crushed apricot pits are not the same compound. What is sold today is generally the latter, and it is not FDA-regulated. NCI notes that batches vary in purity and contents.

"Vitamin B17" is a marketing name, not a scientific one. Ernst T. Krebs Jr. applied that label. It has never been approved as a vitamin by the American Institute of Nutrition.

That distinction matters. Calling something a vitamin implies your body needs it, and that going short of it causes disease. That is the framing behind the claim that cancer is a "vitamin B17 deficiency." There is no such deficiency, because there is no such vitamin.

The proposed mechanism, and why it fails

The theory has an internal logic. That is part of why it persists.

Amygdalin releases hydrogen cyanide when it breaks down. Cyanide kills cells by blocking their ability to use oxygen. That much is real chemistry, and it is the hook. What it leaves out is that cancer is a disease of altered genes rather than an infection that a poison can simply clear, as our page on what cancer is explains.

The specific claim, as NCI's summary describes it, runs like this. Cancer cells are said to carry more beta-glucosidase, the enzyme that frees cyanide from amygdalin. They are also said to carry less rhodanese, the enzyme that detoxifies it. If that were true, the compound would poison tumors and spare healthy tissue.

Some evidence does show that normal and cancerous tissues differ in these enzymes. That is why the idea was worth testing. But a difference in a dish is a long way from a safe margin in a person, and the enzyme that matters most is not in the tumor at all.

Where the cyanide is released turns out to be the whole story. Bacteria in your gut break amygdalin apart, so taking it by mouth releases far more cyanide than injecting it.

NCI's summary describes the experiment that shows this. Germ-free rats given oral amygdalin had no toxicity and no rise in blood cyanide. Normal rats on the same dose became lethargic and had convulsions. The gut flora activates the drug, not the tumor.

What the trials found

Two NCI-sponsored studies were run.

The phase 1 study gave amygdalin to six patients, using the doses and schedules laetrile practitioners were actually using. Toxicity was minimal. Two patients who ate raw almonds during the oral phase developed symptoms of cyanide poisoning.

The phase 2 study was published by Moertel and colleagues in the New England Journal of Medicine in 1982. It enrolled 178 patients. Most had breast, colon, or lung cancer. The great majority were in good general condition, and a third had never had chemotherapy.

They received amygdalin by vein for 21 days, then oral doses. They also received the full metabolic program that went with laetrile in practice: a special diet, vitamins, and enzymes. That design was deliberate. The trial tested the whole package as its advocates delivered it.

One patient had a partial response, lasting ten weeks. By the end of the intravenous course, 54% had measurable disease progression. Every patient had progressed within seven months of finishing it. The authors reported "no substantive benefit" in cure, improvement, stabilization, symptoms, or length of life.

Blood cyanide stayed normal during the intravenous phase. It rose during the oral phase, exactly as the gut-bacteria mechanism predicts. In several patients the levels approached the lethal range.

It is tempting to read a negative trial as proof that nobody looked hard enough. That is not what happened here. Laetrile was tested by a federal agency, in patients well enough to respond, using the protocol its own proponents specified.

The specific harm

The risk is not theoretical. The symptoms of laetrile toxicity are the symptoms of cyanide poisoning: liver damage, nerve damage causing trouble walking, fever, coma, and death.

Risk goes up with oral dosing. It goes up again with raw almonds or crushed fruit pits taken alongside, and with high-dose vitamin C. Because the product is unregulated and batches vary, you do not reliably know the dose you are taking.

The second harm is quieter and often larger. A cancer that is treatable now may not be treatable in six months. Time spent on something that does not work is time the disease is not being treated.

What this does not mean

• Apricots are fine. This is about concentrated extracts and kernels eaten on purpose, not fruit.
• "It's natural" describes where a substance came from, not what it does. Cyanide is natural.
• Wanting more options than your team has offered is reasonable. Raising that with them, including an interest in clinical trials, is a better route than a product sold on a claim that has already been tested and failed.
• Nothing here says anything about supplements in general. It is about one compound with one specific, well-documented failure.

The measures with the strongest evidence behind them are unexciting by comparison. Our overview of cancer prevention covers what actually lowers risk, and the screening overview covers what catches cancer early enough to matter.

Sources

• NCI PDQ: Laetrile/Amygdalin (Patient Version)
• NCI PDQ: Laetrile/Amygdalin (Health Professional Version)
• 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(4):201-6
• Memorial Sloan Kettering: Amygdalin

How this page was made

An AI-assisted editorial system helped prepare this page. No named medical reviewer has reviewed it unless one is listed.

Cancer Explained is published by the National Cancer Information Foundation. It is not medical advice and does not suggest a test or treatment.

See an error, old source, or unclear wording? Tell us.