The chaga mushroom has been used for centuries as a folk medicine remedy in North European countries and Russia. In laboratory studies, chaga demonstrates anti-cancer activity as well as anti-inflammatory, antiviral and immune-stimulating properties, according to the Memorial Sloan-Kettering Cancer Center. This bitter mushroom is sometimes used for pain relief. Always consult a health care provider before trying a medicinal plant, especially if you take medicines or have a health condition, because consuming it may lead to unwanted effects.
Consuming chaga mushrooms may magnify the effects of anticoagulant medications such as aspirin and warfarin. This raises your risk for bleeding and bruising. The active constituents in the mushroom are a combination of triterpenes, including sterols, betulinic acid and polysaccharides, similar to those in the Reishi mushroom, which also raises bleeding risk when taken with anticoagulant or anti-platelet medicines.
Chaga mushrooms also interact with diabetes medicines like insulin, raising your risk for hypoglycemia, or blood sugar levels that fall too low. Symptoms of hypoglycemia may include shakiness, hunger, confusion, dizziness, feeling weak or anxious, and difficulty speaking.
Since the chaga mushroom is not well studied in terms of human consumption, there may be other side effects that are not documented. According to the Memorial Sloan-Kettering Cancer Center in New York, there have been no clinical trials that assess chaga's safety for treating or preventing conditions, including diabetes, cancer or cardiovascular disease, conditions for which the mushroom has a theoretical benefit.
The chaga mushroom, like many other mushrooms, is rich in beta glucans. These have immunomodulating activities. Beta glucans are of interest because they bind to complement receptor 3, or CR3. This allows immune cells in your body to recognize cancer cells as "non-self," which theoretically can trigger cellular death of the cancer cells. Though the side effects of this mushroom are not well studied, other mushrooms that contain beta glucans, such as the Reishi mushroom, can cause a dry mouth and throat, nosebleeds, itchiness, an upset stomach and bloody stools, according to “The Essential Herb-Drug-Vitamin Interaction Guide,” by George T. Grossberg and Barry Fox.