Laetrile is a man-made version of amygdalin named “vitamin B17.” It was widely used as an alternative anticancer drug in the ‘70s. Although proven ineffective and even toxic, its use is still legal. If you want to make informed decisions, read below to uncover the shocking story behind this fraudulent anticancer remedy.

What Is Vitamin B17?

Laetrile is a purported anticancer drug developed in the early 1950s and patented in 1961 by Dr. Ernst T. Krebs and his son Ernst T. Krebs Jr. The compound is derived from amygdalin, the substance that gives bitter almonds their taste. They named it “vitamin B17,” although it is not a vitamin at all [1+].

A popular alternative anticancer therapy in the 70s, its unproven benefits, potential toxicity, and ban by the FDA caused its use to dramatically fall. Although still used as part of “holistic” regimens in a few alternative clinics (mainly in Mexico), Laetrile has been largely abandoned or replaced by apricot seeds as a source of amygdalin [2+].

Amygdalin vs Laetrile vs Vitamin B17

A lot of confusion was created – among fraudulent claims, media portrayal, and scientific research – around the terms amygdalin, laetrile, and “vitamin B17.” Even today, most people are not sure if these substances are all one the same thing or if they’re different in some way.

Here is what you need to know to start with…

Amygdalin is a natural substance found in the seeds of several stone fruits of the Rosaceae family, such as apricots, peaches, almonds, plums, and apples. It is made up of two sugar molecules bound to a compound (mandelonitrile) that releases cyanide when broken down [3+].

Laetrile is a man-made version of amygdalin (mandelonitrile is bound to a sugar derivative called glucuronic acid). However, the product made in Mexico and often sold under the names “Laetrile” and “vitamin B17” is actually amygdalin obtained from crushed apricot seeds [1+, 4+].

Vitamin B17 is the new name that the Krebs gave to Laetrile after suggesting that all cancers are caused by a deficit in this “vitamin”. This name fulfilled several purposes [5+]:

  • Promoting Laetrile as a substance that not only cures but also prevents cancer
  • Escaping strict FDA drug regulations by classifying it as a supplement
  • Exploiting the love affair of the general public with vitamins

However, Laetrile doesn’t fit the scientific definition of vitamin – a substance that is essential to sustain health without supplying energy or building blocks for cells [6+].

Notably, the Krebs had previously patented another “vitamin” (B15 or pangamic acid) and promoted it as a remedy for asthma, eczema, arthritis, and cancer. But as it turns out, not only was pangamic acid not curing any disease, it was more likely causing cancer [7+, 8+].

Early History

Amygdalin was first isolated from bitter almonds in 1830. According to reports, its anticancer effects were tested in Russia and Germany in the 19th century, and it was further researched during the early 20th century [4+, 1+].

In the 1920s, the Californian doctor Ernst T. Krebs “rediscovered” amygdalin while trying to develop a flavoring for bourbon. After noting that amygdalin reduced tumor growth in rats, Krebs started using it in people with cancer. However, he abandoned the remedy because it was too toxic and its effectiveness was unpredictable [1+, 5+].

Over 20 years later, his son Ernst T. Krebs Jr, often referred to as “doctor” but not holding a doctoral degree, developed and patented a man-made, purportedly less toxic analog of amygdalin and named it “Laetrile” (short for “laevorotatory mandelonitrile”) [5+, 2+].

The Rise and Fall of a Cancer Quack

Laetrile owes much of its acquired popularity to Andrew R.L. McNaughton, a Canadian adventurer who started promoting Laetrile after meeting Krebs Jr. McNaughton founded a company to manufacture and distribute the compound [5+].

As a result of McNaughton’s promotion, the journalist Glenn Kittler wrote two articles and a book on the benefits of Laetrile and the doctor Ernesto Contreras opened the first Laetrile clinic in Mexico [9+].

The case of John Richardson, a doctor who was charged for violating California’s Cancer Law by prescribing this compound, triggered the formation of the Committee for Freedom of Choice in Medicine, the first pro-Laetrile organization. Laetrile use spread outside Mexico and California as a result and 70k people had used it by 1978 [5+].

The Supreme Court’s decision to forbid its shipping across borders, the negative results in clinical studies, and unfavorable publicity such as the death of actor Steve McQueen while on Laetrile therapy caused its popularity to fall dramatically [1+, 10, 11].

However, “vitamin B17” still makes its way onto natural health blogs, where its proponents complain about a conspiracy against this remedy. The ongoing petition by Dr Joseph Mercola to acknowledge his studies with Laetrile and the publishing of the book “World without cancer. The story of vitamin B17” keep the myth alive.

Snapshot

PROS

  • May improve inflammatory conditions

CONS

  • Advertised with fraudulent claims
  • Negative results for cancer in clinical studies
  • Toxic when taken by mouth
  • Ineffective when injected
  • Unapproved by the FDA
  • Low quality of some supplements

Do Vitamin B17 Foods Exist?

As a man-made substance, Laetrile (“vitamin B17”) is not found in any foods. Among the amygdalin sources, only almonds (and occasionally apricot seeds) are normally eaten. While regular (sweet) almonds contain only traces of amygdalin, its levels in bitter almonds can reach up to 8 g/kg [12, 13+].

Other foods with measurable but much lower amygdalin levels than bitter almonds include pumpkin seeds and processed products such as apple juice, tinned apricot and peach, and almond milk [14+].

Although the following foods are sometimes mistakenly reported to contain amygdalin, they actually have similar compounds that also release cyanide:

  • Seeds: sorghum, millet, flax [15, 16, 17]
  • Beans: Lima and mung beans [18, 19]
  • Bamboo shoots [20]
  • Macadamia nuts [21]
  • Cassava [22]

These foods may be toxic if you don’t process them sufficiently. However, you’ll greatly reduce their levels of cyanide-releasing compounds by adequately toasting, boiling, fermenting, drying, soaking, or peeling them [23].

See the “Vitamin B17 Side Effects & Safety” section for more information about the dangers of eating amygdalin-containing foods.

How Does It Work?

Fraudulent Anticancer Mechanisms

Both amygdalin and Laetrile can be broken down by an enzyme called beta-glucosidase into mandelonitrile and other compounds. Mandelonitrile is unstable and releases cyanide, which kills cells by blocking an enzyme they require to use oxygen (cytochrome oxidase C) [24, 25+].

Based on this mechanism, Krebs Jr proposed that Laetrile is more toxic to cancer cells because they contain more beta-glucosidase than healthy cells. What’s more, he claimed that only healthy cells have another enzyme called rhodanese that protects them from cyanide by turning it into non-toxic compounds [2+, 26+].

There are several issues with this theory.

For one, healthy and cancer tissues barely break down amygdalin and Laetrile because they contain only traces of beta-glucosidase. Only gut bacteria contain higher levels of this enzyme, which explains why these compounds are toxic by mouth but not injected [27+, 28, 29].

Additionally, it’s uncertain if healthy and cancer tissues have similar rhodanese levels. Older studies suggest that they do, while a few recent studies exist. Some suggest that low rhodanese may be involved in IBS. One recent study did find that rhodanese was less active in colorectal cancer cells, but this was not confirmed clinically [30+, 31+, 32, 33].

In response to objections, Krebs modified his theory to propose that yet another enzyme (beta-glucuronidase) is more abundant in cancers and responsible for Laetrile’s effects. This theory implies that only Laetrile (but not amygdalin) works, since beta-glucuronidase can’t break down amygdalin [2+].

Older studies reported conflicting results about the activity of this enzyme in cancer cells. Scientists are still uncertain about the levels of beta-glucuronidase in healthy vs. cancer cells. Only one recent study reported higher levels of the enzyme in colorectal cancer cells. Thus, Kreb’s modified theory remains unsubstantiated [34, 35, 36, 37, 2+].

Despite the lack of evidence, Krebs renamed the drug “vitamin B17” in 1970. He came up with the theory that cancers are caused by deficits in this “vitamin.” Although never proven, Laetrile’s advocates still accept it as true nowadays [5+, 2+].

Evidence-Based Mechanisms

Anti-inflammatory

Most potential health benefits of amygdalin seen in animal and cell-based studies are due to its anti-inflammatory activity. Amygdalin blocks the major pro-inflammatory pathways( NF-kB and NLRP3) while activating anti-inflammatory ones (Nrf2/NQO1). This reduces the production of inflammatory [38, 39]:

Anticancer

In cancer cells, amygdalin (not Laetrile!) blocked the proteins that promote:

  • Growth (cyclins, CDKs) [44, 45]
  • Survival (Bcl2, survivin, XIAP) [46, 47]
  • Spreading (integrins) [48, 49]

While increasing their sensitivity to free radicals and their production of cancer-fighting proteins (Bax, caspases, PARP) [50, 51, 47].

The mechanism based on cyanide release may also work, but it requires the development of drugs combining amygdalin with beta-glucosidase (to increase cyanide release), cell membrane proteins (to penetrate tissues and reach tumors), and tumor antibodies (to attack tumors but not healthy cells), [52, 53, 54].

Research & the Cancer Cure Hoax

Clinical Studies

The first documented amygdalin use for cancer dates back to 1845. Some anecdotal reports of Laetrile improving cancer during the 1950s and 60s exist, but they often lack essential data for their interpretation [55+, 56+, 57+, 58+].

In 1978, the NCI asked almost 400k doctors in the US to provide cases with positive results for further examination by a panel of doctors. Despite Laetrile’s popularity, only 93 cases were submitted. Of these, 26 were insufficiently documented, 62 had no improvement, and only 6 showed some response to Laetrile [10].

In the only clinical trial ever performed, 175 people with cancer were given amygdalin combined with a special diet. The results were similar to those expected in the absence of therapy: cancer had progressed in 90% of people after 3 months and 80% were dead after 8. Even worse, some of them developed cyanide poisoning [11].

Three recent reviews identified several studies on the use of Laetrile or amygdalin for cancer, but none were sufficiently relevant and well designed. Interestingly, a systematic review of over 200 trials testing amygdalin and other unconventional anticancer substances faced the same problem [59, 60, 61, 55, 62].

To sum it up, clinical evidence suggests that Laetrile or amygdalin do not benefit cancer patients but instead put them at a risk of dangerous cyanide poisoning.

Preclinical Studies

Results in animals were equally disappointing. Amygdalin, both alone and combined with beta-glucosidase, failed to stop cancer progression in 7 out of 8 studies in mice with induced and transplanted tumors [63, 64, 65, 66, 67, 68+, 69, 70].

In turn, the compound reduced the development and growth, blocked the spreading, and increased the death of cancer cells in the following cancer types:

However, these results may very well be irreproducible in clinical trials. While the drug always reaches its target tissue and doesn’t interact with other substances in cells, this is usually not the case in humans. In this particular case, it’s important to note that the studies didn’t check if cyanide damaged healthy cells.

Benefits

Despite the negative anticancer results, amygdalin may have other properties. Indeed, peach seed extract (Tao Ren) is a common ingredient in traditional Chinese remedies for improving blood flow, tissue scarring, and inflammatory diseases.

Below are some preliminary studies investigating its use for these conditions. Note that they may only apply to amygdalin and NOT to Laetrile (or “vitamin B17”).

1) May Improve Blood Flow

Apricot seeds (6x/day) reduced blood pressure in a clinical trial on 72 people. The effect was stronger in combination with 500 mg/day vitamin C, which protects blood vessels and triggers the production of a molecule that relaxes them (NO) [80+].

However, it’s important to note that vitamin C increases the risk of cyanide toxicity. See the “Vitamin B17 Side Effects & Safety” section for more information about this effect.

A traditional Chinese remedy with peach seeds (typically used for blood disorders) reduced blood thickness and blood clotting in rats [81].

2) May Reduce Tissue Scarring

In animal and cells, amygdalin protected the following organs from tissue scarring:

Two traditional Chinese medicines with amygdalin commonly used for tissue scarring in the liver (CGA and Xiayuxue) improved this condition in rats and mice with liver damage [88, 89, 90].

3) May Support Lung Health

Amygdalin protected mice from long- and short-term lung disease by reducing inflammation [38, 87].

Similarly, a traditional Chinese medicine remedy with amygdalin (Mahuang decoction) reduced airway inflammation in asthmatic mice [91].

Very low-weight newborn babies need supplemental oxygen to support breathing because their lungs are very premature. However, the excess of oxygen may damage the lungs. Amygdalin sustained the growth and multiplication of premature lung cells exposed to high oxygen levels [92].

4) May Fight Inflammatory Pain

In rats and mice with inflammatory conditions, amygdalin reduced pain, the levels of a protein produced in nerves in response to pain (c-fos), and the production of inflammatory substances [93, 40, 42].

Endometriosis – the growth of a tissue similar to the uterine lining in other pelvic organs – reduces fertility and increases menstrual pain. Amygdalin combined with a statin drug (atorvastatin) relieved inflammation in rats with this condition [43].

5) May Support Liver Health

By blocking inflammation, amygdalin reduced tissue damage and increased survival in mice with liver injury. In mice with fatty liver disease, it reduced liver damage and blood fat levels but failed to prevent fat buildup in the liver [39, 94].

6) May Reduce Blood Fat Levels

In mice, amygdalin reduced fat and cholesterol levels in the blood and their buildup inside the arteries [95, 96, 94].

The extract of a plant rich in amygdalin (chokeberry) blocked fat cell development and reduced weight gain and fat blood levels in mice fed a high-fat diet [97].

7) May Improve Dry Eye Syndrome

Dry eye syndrome occurs when the eye doesn’t produce enough tears. It’s normally due to the inflammation caused by air pollution particles. In rats and eye cells, amygdalin improved this condition by reducing inflammation [41].

Dosage

In the only clinical trial performed with amygdalin, the doses – based on usual practices by doctors prescribing it – were [11+]:

  • Injected: 3 g, 2x – 5x/day
  • Oral: 500 mg, 3x – 4x/day

Even at these recommended doses, both amygdalin and Laetrile have caused cyanide poisoning when taken by mouth [98+, 99+, 100, 101+].

Apricot seeds haven’t been tested for cancer in clinical trials and there isn’t an official dose. Unofficial recommendations by anecdotal testimonies are in the range of 20-40 seeds throughout the day. The trial testing them for high blood pressure used 6 seeds/day [80+].

In addition to the dangers of using an unproven remedy and basing its dosing on anecdotal information, especially for a condition as serious as cancer, seed amounts as low as 5 20 in adults and 3 in children have caused cyanide poisoning [102+, 103, 104].

Vitamin B17 Legal Status

During its popularity boom in the 1970s, Laetrile advocates started a pro-legalization campaign. As a result, trials were held and the courts of 27 states authorized the production and use of Laetrile. As a drug unapproved by the FDA, Laetrile transport both into the US and across state borders remained forbidden and the black market continued to be its main source [105, 1+].

The case of Glen Rutherford, whose Laetrile was seized by the FDA when bringing it back from Mexico, revived the debate. Although a judge initially ruled that terminally ill patients could transport unapproved drugs across borders with a statement from their doctors, the Supreme Court finally forbade it in all cases [106+, 2+].

Today, Laetrile is banned by the FDA. Its use and possession are legal, but not its transport across borders, sale online, or anticancer marketing claims. For instance, the case of the wrestler Jason Vale, convicted in 2000 for selling Laetrile online, attracted much public attention [107+].

The ban on Laetrile’s transport makes its production within the US unprofitable and most products are made in Mexico. It is, however, legal to buy apricot seeds and supplements made from them.

Additionally, a few clinics in Mexico, Germany, and Thailand still offer “holistic” therapies combining injectable Laetrile with diets and enemas.

Vitamin B17 Side Effects & Safety

Cyanide Poisoning

In compounds like amygdalin, cyanide release depends on the rate of breakdown. Those containing only one sugar molecule (like Laetrile) break down in fewer steps and release cyanide faster than those with two molecules (like amygdalin) [108+].

In any case, both substances have caused cyanide toxicity in people with cancer or children taking them accidentally. The main symptoms were [11+, 100, 99, 109, 110+, 111+]:

  • Fever
  • Headache
  • Nausea and vomiting
  • Low blood pressure
  • Difficulties breathing
  • Skin rash
  • Muscle weakness and damage
  • Nerve damage
  • Drooping eyelids
  • Liver damage
  • Confusion, coma, and even death

From Foods

Natural amygdalin sources such as apricot seeds have also caused cyanide poisoning with similar symptoms [102, 103, 104, 112, 113, 114+].

In the case of seeds, the risk of poisoning is higher because they contain both amygdalin and beta-glucosidase. Although they are in different cells, chewing the seeds breaks the tissues and allows both substances to mix [108+].

While oral amygdalin often causes cyanide poisoning, injected remedies might be less toxic (to both healthy and cancer cells) since amygdalin is flushed with urine without being digested in the gut [115+, 2+].

The toxic effects of Laetrile may be enhanced in combination with foods that increase cyanide levels. This includes those rich in [116, 117]:

  • Cyanide-releasing compounds (almonds, macadamia nuts, millet, cassava)
  • Beta-glucosidase (carrots, celery, bean sprouts, peaches)

Additionally, vitamin C (either in supplements or foods such as citruses, kiwis, and strawberries) increases amygdalin toxicity by speeding cyanide release and reducing the levels of an amino acid that detoxes cyanide (cysteine) [118, 119, 120].

People at an increased risk of cyanide poisoning also include those with:

Other Risks

It’s especially dangerous to replace approved anticancer therapies with Laetrile or amygdalin. Two kids with high chances of surviving leukemia relapsed and died after their parents decided to give them Laetrile instead of chemotherapy [123+, 124+, 125].

Since Laetrile is not approved by the FDA, its manufacturing is not regulated and many products may be unsafe for clinical use. Indeed, an analysis of several tablets and injections produced in Mexico revealed that they were insufficiently powerful, poorly manufactured, and often contaminated with microorganisms [126].

In pregnant hamsters, oral but not injected Laetrile caused malformations in the offspring. In the only case reported in humans, a pregnant woman receiving Laetrile injections gave birth to a healthy baby. Due to the lack of safety data, its use during pregnancy should be avoided [115, 127].

Limitations and Caveats

The successful stories of Laetrile as an anticancer drug are all based on anecdotal evidence often lacking essential data such as the number of patients or the follow-up period. Similarly, all systematic reviews failed to find trials that were well-designed and documented.

All the other potential health benefits are insufficiently investigated. Amygdalin’s effect on blood pressure was tested in only one clinical trial that didn’t include a negative control, while the rest have only been investigated in animals and cells. More clinical trials are required to validate these results.

Reviews

Since it’s illegal to sell Laetrile or amygdalin online, only reviews of apricot seeds or products derived from them (mainly capsules and oil) are available. For legal reasons, the products are not advertised as anticancer drugs but as nutritious dietary supplements with vitamin B17.

People usually took in the seeds and capsules to help fight or prevent cancer. A lot of them were convinced that the product was helping – although they provided little information on its effects and additional therapies – and normally gave it good ratings.

The main complaint among dissatisfied users was the bitter taste of the seeds. Several of the negative reviews warned potential users that B17 is not a real vitamin and its effects on cancer are not proven.

The oil was mainly bought for its softening effects on the hair and skin and normally received positive reviews. A few users reported drinking it because they thought it helped fight cancer.

Take-Away:

Laetrile, also known as vitamin B17, is a man-made version of the natural substance amygdalin. It’s not actually a vitamin. Developed in the ‘50s by Dr. Ernst T. Krebs and his son, its use as an alternative remedy for cancer was popularized in the ‘70s.

But this “miracle cure” turned out to be a hoax. Clinical studies failed to find any effects other than that it causes cyanide poisoning when used orally. Far from being an effective anticancer drug, this compound can be dangerous.

The controversy between advocates and opponents brought Laetrile before the court. Its use and possession were approved, but it can’t be transported across borders, sold online, or advertised as a cancer-healing product.

Today, only a few clinics still use Laetrile in “holistic” therapies. It has largely been replaced by apricot seeds, which may have some health benefits but aren’t harmless either.

About the Author

Carlos Tello, PhD (Molecular Biology)

PhD (Molecular Biology)

Carlos received his PhD and MS from the Universidad de Sevilla.

Carlos spent 9 years in the laboratory investigating mineral transport in plants. He then started working as a freelancer, mainly in science writing, editing, and consulting. Carlos is passionate about learning the mechanisms behind biological processes and communicating science to both academic and non-academic audiences. He strongly believes that scientific literacy is crucial to maintain a healthy lifestyle and avoid falling for scams.

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