Wild shiitake mushrooms are native to Japan, China, and other Asian countries and typically grow on fallen broadleaf trees. Shiitake is now widely cultivated throughout the world, including the United States. The fruiting body is used medicinally.

Shiitake has been revered in Japan and China as both a food and medicinal herb for thousands of years. Wu Ri, a physician from the Chinese Ming Dynasty era (A.D. 1368–1644), wrote extensively about this mushroom, noting its ability to increase energy, cure colds, and eliminate worms.¹

Shiitake contains proteins, fats, carbohydrates, soluble fiber, vitamins, and minerals. In addition, shiitake’s key ingredient—found in the fruiting body—is a polysaccharide called lentinan. Commercial preparations employ the powdered mycelium of the mushroom before the cap and stem grow. This preparation is called lentinus edodes mycelium extract (LEM). LEM is rich in polysaccharides and lignans.

One preliminary trial suggested that oral shiitake may be useful for people with hepatitis B.⁴ A highly purified, intravenous form of lentinan is used in Japan and has been reported to increase survival in people with recurrent stomach cancer, particularly when used in combination with chemotherapy.⁵ Similar findings have been found in one small clinical trial with people suffering from pancreatic cancer.⁶ Case reports from Japan suggest that intravenous lentinan may be helpful in treating people with HIV infection.⁷ However, large-scale clinical trials to confirm this action have not yet been performed.

Oral supplementation of lentinan from shiitake has been shown to significantly reduce the recurrence rate of genital warts (condyloma acuminata). A preliminary trial involving a group of men and women with genital warts found that those who took 12.5 mg of lentinan twice a day for two months after laser surgery had significantly fewer recurrences (10.53% recurrence rate) compared to those who only had the laser surgery (47.06% recurrence rate).⁸

The traditional intake of the whole, dried shiitake mushroom is 6–16 grams per day.⁹ The mushroom is typically eaten in soups or taken as a decoction (i.e., boiled for 10–20 minutes, cooled, strained, and drunk). Recommended intake of LEM is 1–3 grams two to three times per day. Purified lentinan is considered a drug in Japan and is not currently available as an herbal supplement in North America.

Shiitake has an excellent record of safety but has been known to induce temporary diarrhea and abdominal bloating when used in high amounts (above 15–20 grams per day). Its safety during pregnancy and breast feeding has not yet been established.