Ganoderma lingzhi
Reishi mushrooms are a popular fungus in Eastern medicine that have been used to treat a variety of conditions. Some of the claimed benefits of reishi mushroom include:  
Immune system: Reishi mushrooms may increase the number and activity of white blood cells, which help fight viruses and bacteria.  
Cancer: Reishi mushrooms contain beta-glucans, which may slow or stop tumor growth.  
Fatigue: Reishi mushrooms may help reduce fatigue.  
Sleep: Reishi mushrooms may improve sleep.  
Depression: Reishi mushrooms may help relieve depression symptoms.  
Energy: Reishi mushrooms may help boost energy levels.  
However, some research has not supported the use of reishi mushrooms for other conditions, such as:  
Cardiovascular risk factors
Randomized controlled trials have not shown that reishi mushrooms reduce cardiovascular risk factors associated with type 2 diabetes.  
Fibromyalgia
Reishi mushrooms did not influence blood or anthropometric measurements in patients with fibromyalgia.  
Cholesterol, blood sugar, and antioxidants
Most human research has shown that reishi mushrooms do not improve cholesterol, blood sugar, or antioxidants. 
Reishi mushrooms are among several medicinal mushrooms that have been used for hundreds of years, mainly in Asian countries, for treatment of infections. More recently, they have also been used in the treatment of pulmonary diseases and cancer. Medicinal mushrooms have been approved adjuncts to standard cancer treatments in Japan and China for more than 30 years and have an extensive clinical history of safe use as single agents or combined with chemotherapy.
Reishi mushrooms can slow blood clotting, which can increase the risk of bleeding when taken with other blood thinners like warfarin. Doctors recommend stopping reishi mushroom use at least two weeks before surgery. 
 
CANCER STUDIES
There are several studies on reishi mushrooms and cancer, including: 
Immune cell activity
A review of five randomized trials found that reishi mushrooms increased the activity of immune cells when given with chemotherapy and radiotherapy. However, the review also stated that more high-quality trials are needed before reishi mushrooms can be considered a cancer treatment. 
Benign colorectal tumors
A study in Japan found that patients with benign colorectal tumors who took an extract of reishi mushrooms for 12 months had a decrease in the number and size of their tumors. 
Breast cancer
A study found that reishi mushrooms may suppress tumor growth in breast cancer by affecting protein synthesis and survival pathways. 
Aromatase inhibitor-associated toxicities
The Minnesota Cancer Clinical Trials Network funded a study to evaluate reishi mushrooms as a treatment for toxicities associated with aromatase inhibitors in breast cancer.