Reishi

What it is

Reishi (also called lingzhi) is a woody mushroom, Ganoderma lucidum, that has been used in traditional Chinese medicine for more than 2,000 years [1]. It is sold as dried powder, hot-water or alcohol extracts, spore powder and spore oil. Its main active compounds are thought to be triterpenoids and polysaccharides (long chains of sugars) [2].

How it might work

Proposed mechanisms, not proven in people: the triterpenoids and polysaccharides may reduce oxidative stress (damage from reactive molecules) and shift the activity of immune cells [2] [3].

What the research says

Antioxidant status and fitness. The most consistent positive signal is in antioxidant markers. A 2025 meta-analysis (a study that pools many trials) of 17 randomised trials with 971 people found reishi raised glutathione peroxidase, an antioxidant enzyme (WMD +2.29, 95% CI 1.67 to 2.92), and lowered body mass index slightly (−0.43) and resting heart rate (−3.92 beats per minute); the authors rated certainty as very low for every outcome [4]. In 42 healthy adults, six months of a triterpenoid-enriched capsule raised plasma antioxidant capacity, lowered a marker of fat oxidation (TBARS 3.37 to 2.47) and cut liver enzymes GOT and GPT by 42% and 27% [2]. On fitness, 78 female college students taking 1,000 mg a day for 30 days improved VO2max (a measure of aerobic fitness), work capacity and grip strength compared with placebo, and reported lower anxiety and depression scores [5]. In 64 women with fibromyalgia, 6 g a day for 6 weeks improved aerobic endurance, lower-body flexibility and speed [6].

Cholesterol and triglycerides. A 12-week trial of 110 people with raised blood fats found that reishi spore oil softgels lowered triglycerides (1.51 vs 1.88 mmol/L), LDL cholesterol (2.68 vs 3.20 mmol/L) and total cholesterol (4.87 vs 5.25 mmol/L) compared with placebo [7]. An earlier crossover trial of 23 people saw triglycerides fall and HDL rise on reishi, but carry-over between treatment periods stopped the authors from analysing these results fully [8]. Two other analyses found nothing: a Cochrane review (an independent review of trials) found no change in total cholesterol or LDL in people with type 2 diabetes [1], and the 2025 meta-analysis found no pooled effect on lipids [4]. A 6-week trial in women with fibromyalgia also found no change in cholesterol or triglycerides [9].

Blood sugar and blood pressure. These are the best-tested claims, and they came out negative. The Cochrane review of 5 trials (398 people) found no meaningful drop in HbA1c, a three-month blood sugar measure (−0.10 percentage points, 95% CI −1.05 to 0.85), and no difference in blood pressure [1]. A 16-week placebo-controlled trial of 84 people with type 2 diabetes and metabolic syndrome, taking 3 g a day, also found no effect on HbA1c or fasting glucose [10]. The 2012 crossover trial found lower insulin and insulin resistance on reishi, but no change in blood pressure [8].

Immune function. In cancer patients, a Cochrane meta-analysis found reishi alongside standard treatment raised the share of CD3, CD4 and CD8 immune cells by about 2 to 4 percentage points [11]. In people without cancer, results were mixed: 23 adults with borderline blood pressure or cholesterol showed no difference in lymphocyte subsets [8], while in 39 older women 2,000 mg a day for 8 weeks shifted T-cell gene activity toward an anti-inflammatory pattern without increasing T-cell proliferation [3]. These are lab markers, not fewer infections.

Cancer. The Cochrane review of 5 trials found patients given reishi alongside chemotherapy or radiotherapy were somewhat more likely to respond than those on conventional treatment alone (RR 1.50, 95% CI 0.90 to 2.51), and four trials reported better quality of life. No trial measured survival, and the trials were of poor quality, so the reviewers did not support reishi as a first-line treatment [11].

Alzheimer's disease. In a pilot trial of 42 people with Alzheimer's, 6 weeks of reishi spore powder did not improve memory and thinking scores (ADAS-cog p = 0.31) or quality of life compared with placebo [12].

Doses used in studies

Doses vary widely. The 2025 meta-analysis pooled trials using 200 to 11,200 mg a day for 1 to 24 weeks [4]. The Cochrane review of blood sugar trials covered 1.4 to 3 g a day for 12 to 16 weeks [1]. The fitness trial in students used 500 or 1,000 mg a day for 30 days [5]. The older-women immune trial used 2,000 mg of dry extract a day for 8 weeks [3], and the fibromyalgia trials used 6 g a day of powder for 6 weeks [6]. These are doses studied, not recommendations.

Safety and interactions

Side effects. In trials reishi was generally well tolerated. In the Cochrane cardiovascular review, people taking reishi for four months were 1.67 times as likely to report an adverse event as those on placebo (95% CI 0.86 to 3.24), and none were serious [1]. The cancer review reported minimal side effects such as nausea and insomnia and no significant blood or liver toxicity [11].

Liver injury. Case reports describe serious liver damage. Two patients developed hepatitis after switching from boiled reishi to reishi powder for one to two months, and one of them died; both were also taking other treatments [13]. A 47-year-old man developed acute hepatitis after taking reishi powder together with alcohol and recovered fully in two weeks [14]. Case reports cannot show how often this happens or prove reishi was the cause.

Upper limits, medicines, pregnancy and other conditions. The highest dose in the pooled trials was 11.2 g a day [4], and no official upper intake limit was identified in the studies reviewed. No dedicated studies of interactions with medicines, of use in pregnancy or breastfeeding, or of use in people with bleeding disorders were found. Because of the liver reports, people with liver disease or who drink alcohol regularly, and anyone taking other liver-affecting products, may want to ask a doctor first.

Caveats and open questions

Most trials are small and short, and products differ (fruiting body powder, extract, spore powder, spore oil), so results from one form may not apply to another [4]. The authors of the 2025 meta-analysis rated the certainty of evidence as very low for all outcomes [4]. The positive cholesterol and liver-enzyme results come from single trials that other analyses did not reproduce [7] [2] [4]. An ongoing trial is testing reishi extract for fatigue and joint pain in cancer patients.