Reishi is a dark mushroom whose botanical name is Ganoderma lucidum. Reishi is considered an adaptogen, a compound that may help the body cope with stress and boost the immune system.
Reishi mushroom is important in traditional medicine systems of several countries in Asia, including China, Japan, and Korea.
Other names for this mushroom include red reishi, basidiomycetes mushroom, ling zhi, or ling chih (in China), and mannentake (in Japan).
People can eat the whole mushroom, but powdered forms or extracts are mostly commonly used in traditional or alternative medicine.
(See also Overview of Dietary Supplements.)
Claims for Reishi
Proponents of reishi mushroom claim that it can benefit health in many ways, including the following:
Boost the immune system (although what this means or how this could be done is not clear) to prevent or treat infections
Treat fatigue
Lower high cholesterol and blood pressure
Increase strength and stamina
Treat HIV and AIDS
Prevent or treat cancer
Reduce inflammation
Evidence for Reishi
Any single compound, including reishi, is highly unlikely to have such a broad range of health benefits. Thus, evidence is very unlikely to confirm such multiple benefits.
Studies in animals and cells have shown that reishi can protect the kidneys and liver from damage, kill cancer cells, and help fight infections.
Studies in people have not confirmed these findings.
The evidence from studies in people to show that reishi has the claimed health benefits is limited. Many of these studies are small and of poor quality, and some have contradicted the findings of others.
A well-conducted review found that the evidence was insufficient to show that reishi can be used as the initial treatment for cancer. The evidence does not show whether reishi can prolong survival in people with cancer.
Small studies with weak designs have also shown that reishi mushroom treatment reduces pain and promotes the healing of painful varicella-zoster lesions in older adults. Other small studies have found that reishi might reduce fatigue and improve quality of life in people who have had breast cancer. Other evidence indicates that reishi may help relieve urinary tract symptoms in men with an enlarged prostate.
Side Effects of Reishi
Taking reishi mushroom extract for up to a year might be safe, but taking the powdered form of reishi for more than a month could damage the liver.
Other side effects of reishi mushrooms include dry mouth, rashes, upset stomach, diarrhea, headache, nosebleed, and dizziness.
The safety of reishi mushroom in pregnant women and women who are breastfeeding has not been thoroughly studied.
High doses of reishi could increase bleeding risk in people with certain bleeding disorders, including thrombocytopenia (low level of platelets in the blood).
Taking high doses of reishi before or during surgery could increase the risk of bleeding.
Because reishi might reduce blood pressure, it might worsen low blood pressure in people whose blood pressure is already low.
Drug Interactions with Reishi
Reishi could make some chemotherapy drugs less effective (although conversely it may make some chemotherapy drugs more effective).
Reishi may interfere with a lab test for a serum tumor marker (CA72-4) that indicates the presence of certain types of cancers.
In animal studies, reishi may interact with diabetes medications to decrease blood sugar. This has not been shown in humans.
Recommendations for Reishi
There appears to be no compelling reason to take reishi for most people.
The claimed health benefits of reishi have not been confirmed in high-quality studies in people.
However, reishi is probably safe for most people; even so,
Pregnant and breastfeeding women, people with low blood pressure or certain bleeding disorders, and those who are undergoing surgery should avoid reishi.
People who take certain medications (including medications to slow blood clotting and chemotherapy drugs) should talk to their doctor before taking reishi.
