Reishi mushrooms are rare mushrooms that grow at the base of deciduous trees. Some people claim that reishi mushrooms can boost the immune system, fight cancer, and relieve symptoms of many other health conditions.

Despite the popularity of reishi mushrooms in Eastern medicine, there are limited human studies on the effects of this fungus. There is also growing evidence to suggest that reishi mushrooms may be toxic and cause health issues.

Keep reading for more information on the possible benefits of reishi mushrooms, as well as the side effects and risks.

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Reishi mushrooms are popular in Eastern medicine.

Reishi mushrooms (Ganoderma lucidum) have been a part of some traditional medicine practices for more than 2,000 years.

According to one review article, reishi mushrooms contain polysaccharides, peptides, and triterpenoids, which may provide some of their health benefits. They also contain dietary fiber and various minerals, vitamins, and amino acids.

People grind them into powder or use extracts to make supplements and other products. While their use is widespread, the evidence supporting any benefits is still lacking.

Most researchers have done studies either on animals or in labs. The few human studies to date have not reproduced the same results, indicating that the mushrooms may not be as beneficial for humans.

Reishi mushrooms are best-known for their purported effects in boosting the immune system and helping fight off cancer. However, studies do not support the alleged benefits of reishi mushrooms.

The Susan G. Komen foundation, a cancer charity, has found insufficient or no evidence that reishi mushrooms are effective in:

The Memorial Sloan Kettering Cancer Center also state that there is little or no evidence to suggest that reishi mushrooms treat:

However, research is ongoing on the potential benefits of reishi mushrooms. Laboratory test-tube studies have found that they could be effective in fighting cancer and shrinking tumors.

There is also evidence from in vitro and animal studies that reishi mushrooms may support the immune system, but high quality studies in humans are necessary before researchers draw any conclusions.

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An upset stomach is a possible side effect of taking reishi mushroom.

Many side effects of reishi mushrooms remain unknown due to the limited body of research in humans.

One review of studies found that reishi mushrooms may help with boosting the immune system, but the authors would not recommend them as a first response to cancer. A few people reported side effects, which included:

The Susan G. Komen Foundation note that reishi mushroom extract is possibly safe for up to 1 year when a person takes it orally. However, they also note that taking powdered reishi mushroom for longer than 1 month may be toxic to the liver.

Other potential side effects include:

  • nausea
  • insomnia
  • chronic diarrhea
  • liver toxicity
  • dryness in the mouth, throat, and nose
  • itchiness
  • nosebleeds
  • bloody stool

Liver toxicity is a dangerous side effect that can lead to death.

The right dosage of reishi mushroom extract or powder can vary widely depending on which form of the mushroom a person uses. It is important to check the label of the specific product for the recommended dosage.

Before taking a reishi mushroom supplement, a person should talk to a doctor. Supplements can interact with other medications, potentially causing adverse effects, and worsen some health conditions.

A doctor may be able to recommend alternative therapies and treatments that work better for people based on their medical history.

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When buying reishi mushrooms, people should check for additional ingredients or unknown substances.

There are several risks and considerations to keep in mind before taking reishi mushrooms.

Reishi supplements may cause anticoagulants or antiplatelets to become more effective, which increases the risk of bleeding. Therefore, people whom doctors have scheduled for surgery and individuals with bleeding disorders should not take reishi mushrooms.

These supplements might also lower blood pressure. People who already have low blood pressure or are taking blood pressure medication may wish to avoid reishi mushrooms.

This advice also applies to those taking immunosuppressants, as reishi mushroom supplements may counteract their effectiveness.

Also, women who are pregnant or breastfeeding should not consume these mushrooms.

People should carefully consider the dangerous side effects above before trying reishi mushroom supplements.

It is important to note that the Food and Drug Administration (FDA) do not monitor supplements and natural remedies. Depending on where a person purchases them from, they may contain additional ingredients or unknown substances.

Many people believe that reishi mushrooms provide some health benefits, primarily immune system enhancement and cancer treatment. However, it is vital to note that there is limited evidence to support any of the claims about their effectiveness.

Reishi mushrooms may be harmful to people who have bleeding issues, are pregnant, or take certain medications.

Before trying reishi mushrooms, it is best to speak to a doctor about the safety and risks.