Laetrile is often wrongly called amygdalin or vitamin B17.

Rather, it is a drug that contains purified amygdalin — a compound found in the seeds or kernels of many fruits, raw nuts, beans and other plant foods (1, 2).

Laetrile is best known as a controversial treatment for cancer. However, there is little scientific evidence to support this hefty claim (1).

This article explains everything you need to know about laetrile, backed by science.

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Laetrile is the name of a drug created in 1952 by Dr. Ernst T. Krebs, Jr. (3).

It contains purified amygdalin, which is a compound found naturally in the following (1, 4):

  • Raw nuts: Such as bitter almonds, raw almonds and macadamia nuts.
  • Vegetables: Carrots, celery, bean sprouts, mung beans, lima beans and butter beans.
  • Seeds: Millet, flaxseeds and buckwheat.
  • Pits of: Apples, plums, apricots, cherries and pears.

You can take laetrile as a pill or receive it as an injection into the veins or muscles (1).

It is a controversial cancer treatment that was popular in the 1970s. However, it was banned in many US states after research deemed it ineffective and potentially poisonous (3, 5).

When laetrile passes through the body, it is converted into hydrogen cyanide — a compound that can prevent cells from using oxygen and eventually kill them (1, 6).

Some theories suggest that hydrogen cyanide may have anticancer effects. Yet, these theories don’t have much evidence to support their claims (7, 8).

Interestingly, there is some evidence that laetrile may provide health benefits. Studies have found that it may help reduce blood pressure, relieve pain and boost immunity (9, 10, 11).

Summary Laetrile is a drug that contains purified amygdalin. It is converted by the body into hydrogen cyanide, which is said to be the source of its suggested anticancer effects.

The body breaks down laetrile into three compounds: hydrogen cyanide, benzaldehyde and prunasin (2).

Hydrogen cyanide appears to be the main compound responsible for its health benefits. It is also thought to be the primary anticancer ingredient in laetrile (12).

Certain enzymes in the body convert hydrogen cyanide into a less toxic molecule called thiocyanate. This molecule was previously used to treat blood pressure, as it may dilate blood vessels. It was later discontinued because of its toxic effects (13, 14, 15).

There are four possible theories on how laetrile may fight cancer, though these theories are not supported by scientific evidence.

Two theories state that cancer cells are rich in enzymes that convert laetrile into cyanide. Since cyanide kills cells, this means that cancer cells may break down laetrile and kill the cancer (7, 8).

However, there is no evidence that cancer cells contain the enzymes that help convert laetrile into cyanide (16, 17).

The third theory suggests that cancer is caused by a deficiency in vitamin B17 (amygdalin).

No evidence proves that amygdalin is actually a vitamin. It is also not naturally found in the body, and your body cannot be deficient in amygdalin (18, 19, 20).

The last theory proposes that hydrogen cyanide, which is made by breaking down laetrile, will make cancer cells more acidic and cause them to die.

But hydrogen cyanide does not differentiate and may also kill healthy cells as well as cancer cells (21).

Summary It’s not clear how laetrile may help fight cancer. However, a few theories suggest that it may specifically target cancer cells or treat nutritional deficiencies.

While most of the research on laetrile focuses on its effects on cancer, some studies have found that amygdalin, the natural form of laetrile, may have other health benefits.

Here are a few possible health benefits of amygdalin:

  • It may lower blood pressure: In one study, amygdalin helped lower systolic blood pressure (upper value) by 28.5% and diastolic blood pressure (lower value) by 25%. These effects were enhanced when taken with vitamin C (9).
  • It may relieve pain: Several animal studies show that amygdalin may help relieve pain caused by inflammatory conditions, such as arthritis. However, there is a lack of human-based evidence in this area (10, 22).
  • It may boost immunity: A test-tube study found that amygdalin improved the ability of immune cells to adhere to prostate cancer cells (11).

Keep in mind that the benefits above are only supported by weak evidence. More studies on laetrile and its health benefits need to be done before recommendations can be made.

Summary Some evidence shows that laetrile may help lower blood pressure, relieve pain and boost immunity. However, more human studies are needed.

Laetrile is often wrongly called vitamin B17. It is actually a patented drug that was invented by Dr. Ernst T. Krebs, Jr. in 1952.

During the 1970s, Dr. Krebs falsely claimed that all cancers are caused by a vitamin deficiency. He also claimed that laetrile was the missing vitamin in cancer, which he then called vitamin B17 (23).

He likely labeled laetrile as vitamin B17 so that it would be classified as a nutritional supplement, rather than a medicine. This is likely because the tough federal laws that apply to marketing drugs do not apply to supplements.

Interestingly, Dr. Krebs and his father had previously created vitamin B15, or pangamic acid. This was another supplement that claimed to cure a variety of diseases (23, 24).

Summary Laetrile was likely called vitamin B17 so that it could be marketed as a nutritional supplement, rather than a medicine. This allowed it to avoid tough laws that apply to marketing drugs.

During the 1970s, laetrile was a popular alternative treatment for cancer (8).

However, it is now banned by the Food and Drug Administration (FDA) in many states. This is because laetrile can cause severe side effects. Not to mention, there is no evidence that shows it can effectively treat cancer (3, 5, 25).

In two animal studies, scientists treated a variety of cancers with laetrile alone or combined with an enzyme that helps activate it. In both studies, animals did not show any improvement after being treated with laetrile (26, 27).

Additionally, the animals seemed to experience more side effects when they received both the enzyme and laetrile, rather than laetrile alone.

Currently, only two studies have examined the effects of laetrile on cancer in humans, though neither compared it to a placebo treatment. Thus, it's not clear if taking laetrile is better than receiving no treatment at all (28).

In one study, 178 people with cancer were treated with laetrile. Scientists found that it had no significant effect on cancer. In fact, some people experienced cyanide poisoning (29).

In the other study, six people with cancer were treated with laetrile. Scientists found that laetrile did not help treat cancer, as each individual’s cancer continued to spread (30).

There are some reports that say laetrile helped treat cancer. Nevertheless, these reports also weren’t able to prove that it was laetrile alone that helped (28).

Lastly, a few test-tube studies have shown that laetrile may reduce the occurrence of tumors by suppressing genes that help them spread. However, there’s no evidence that this same effect will occur in living human bodies (31, 32, 33).

Overall, the evidence shows that laetrile is ineffective at treating cancer. It is also very dangerous, as it has the potential to be highly toxic and cause death.

Summary Most evidence clearly shows that laetrile is ineffective at treating cancer in human and animal studies. While there are some reports of laetrile helping treat cancers, they aren’t based on proper scientific studies.

Laetrile is known to have various side effects (34, 35, 36, 37).

Most of these side effects are caused by too much hydrogen cyanide in the body. That’s why the symptoms of laetrile poisoning are the same as cyanide poisoning (8).

Side effects include (1):

  • Nausea and vomiting
  • Headaches
  • Dizziness
  • Bluish skin caused by oxygen deprivation
  • Liver damage
  • Abnormally low blood pressure
  • Droopy upper eyelid (ptosis)

Side effects are worsened by (1, 2):

  • Taking laetrile as a pill, rather than as an injection
  • Eating raw almonds or crushed fruit pits while taking laetrile
  • Taking too much vitamin C while taking laetrile
  • Eating fruits or vegetables that may enhance the effects of laetrile, such as carrots, bean sprouts, celery and peaches

Research shows that vitamin C can interact with laetrile and increase its toxic effects.

Vitamin C speeds up the conversion of laetrile into hydrogen cyanide. It also depletes the body's stores of cysteine, an amino acid that helps the body detoxify hydrogen cyanide (38, 39).

In some cases, taking laetrile (and amygdalin) has led to death through cyanide poisoning (40, 41).

Summary Laetrile can cause a variety of side effects, which are worsened by taking it as a pill or with too much vitamin C. Raw almonds, crushed fruit pits and certain fruits and vegetables can also worsen symptoms.

Laetrile (amygdalin) is a highly controversial alternative cancer treatment.

It is banned in many states by the FDA because it is ineffective at treating cancer and may cause cyanide poisoning.

Laetrile comes with very serious health risks that may potentially lead to death. Thus, it should be avoided.