What it's actually good for
Reishi (Ganoderma lucidum) has one of the longest traditional-use records of any medicinal mushroom, and modern research has at least confirmed that its two main compound classes do something measurable. Beta-glucan polysaccharides engage receptors on macrophages and NK cells; triterpenes (ganoderic acids) inhibit NF-κB and MAPK inflammatory signaling. A 2026 preclinical systematic review (Pozzobon et al.) pooling 23 cellular and animal studies confirmed the triterpene anti-inflammatory mechanism is real and reproducible — but noted poor bioavailability as a barrier to translating it into human effects, and found no human clinical data on that pathway at all. That gap between "does something in a dish" and "does something in a person" is the story of reishi generally: mechanistically plausible, traditionally well-regarded, and thinly tested in rigorous human trials.
What the research says
Immune modulation (Grade C — one solid trial, not yet a body of evidence). The best human data here is a 2023 randomized, double-blind, placebo-controlled trial (Chen et al., Foods) in 157 healthy adults given 200 mg/day of a standardized reishi beta-glucan extract for 84 days. The treatment group showed real increases in CD3+/CD4+/CD8+ T-cell counts, NK cell cytotoxicity (up 83% versus placebo), and IgA, with no adverse changes to liver or kidney markers. That's a well-designed trial with a meaningful sample size, and it's the strongest single piece of clinical evidence behind reishi's immune claim. But it's one trial in healthy volunteers measuring immune cell activity, not infection rates or symptom outcomes — it shows reishi does something to circulating immune markers, not that it prevents colds or flu. One good trial doesn't make a settled case.
Sleep and stress (thinner). The sleep claim leans on small trials with soft endpoints — well-being scores, fatigue questionnaires, subjective sleep quality — rather than polysomnography or infection/illness endpoints. An older RCT in patients with neurasthenia (a nonstandard fatigue diagnosis) found reishi polysaccharide reduced fatigue and improved well-being versus placebo; more recent small trials in stressed populations report similar soft-outcome improvements. None of it clears the bar for anything above a C on the sleep claim specifically.
Cancer (the best-studied use case, and still weak). A 2016 Cochrane review of Ganoderma lucidum in cancer patients — five RCTs, 373 participants — rated the evidence low to very low quality, useful mainly as insufficient to recommend it as treatment on its own. That doesn't speak to the immune or sleep claims directly, but it's the field's most rigorous human investigation of reishi, and it found the same pattern this whole entry does: interesting biological signal, not enough methodological rigor to draw firm conclusions.
How much, and which form
Typical doses run 1,000–3,000 mg/day of extract, or 1.5–9 g/day of dried whole mushroom — a wide range because studies use wildly different preparations. Look for hot-water or dual (water + alcohol) extracts: water pulls out the beta-glucans, alcohol pulls out the triterpenes, and a water-only extract misses the triterpenes almost entirely. Fruiting-body extracts are generally preferred over mycelium-on-grain products, which can be diluted with starch from the growth substrate.
Safety & interactions
Reishi has been well-tolerated in studies running up to a year, with occasional GI upset or dizziness. Rare case reports link powdered reishi products to liver toxicity, so anyone with existing liver disease should be cautious and talk to a clinician first. Because it may potentiate anticoagulant and antiplatelet drugs, stop it before surgery and check with a doctor if you're on blood thinners. The immune-modulating mechanism also creates a theoretical interaction risk with immunosuppressants. This is informational, not medical advice — talk to a clinician before starting, especially if pregnant, nursing, on medication, or managing a chronic condition.
How we picked the brand
A reishi product earns a spot when it's a fruiting-body (not mycelium-on-grain) hot-water or dual extract with a stated beta-glucan percentage, backed by independent third-party testing.