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Fungi of the Month · Edition 01 · July 2026

Reishi — What the Trials Show, and the Liver Warning

Sold for immunity, stress, sleep and the liver. In people, there are small trials for fatigue and poor-quality trials alongside cancer treatment, no benefit for cholesterol or blood sugar, and case reports of liver injury. Here is what each claim rests on.

Stephen Duncan
BSc (Hons) · PG Dip · MSc · FDN-P
July 2026 · corrected October 2026
Corrected October 2026
This edition first described a 2003 study as a randomised trial in lung cancer that "showed significant NK cell activation". It was an uncontrolled study in mixed advanced cancers. The same team's 2005 lung-cancer study found no significant change in NK activity. The page also called reishi "hepatoprotective" without mentioning case reports of liver injury, and it named two brands. Those are corrected below, every claim is graded, and a "How much" block is added. What changed and why →
Disclosure
Detective Health has commercial relationships with Amrita, Longevity Essentials and Synergistics, who sell medicinal mushroom products. Nothing below is a recommendation to buy any of them.

Reishi (Ganoderma lucidum) has been used in East Asian medicine for a very long time, and it's sold today for immunity, stress, sleep and the liver. It gets oversold by one side of the supplement industry and dismissed out of hand by the other. This edition sets out what has been tested in people, what has only been seen in the lab, and what has gone wrong.

What's in it

Two main compound groups
Beta-glucans and triterpenes
Beta-glucans (polysaccharides): shared with other medicinal mushrooms. In the lab they bind receptors on immune cells (Dectin-1). Grade: mechanistic. The human studies below used polysaccharide extracts.
Triterpenes (ganoderic acids): specific to Ganoderma species. Cell and animal studies report effects on liver cells, cholesterol synthesis and histamine release. Grade: mechanistic, cell and animal. None of these effects has been shown to matter clinically in people.
Extraction: polysaccharides come out in hot water; triterpenes dissolve far better in alcohol. So a hot-water-only extract will be low in triterpenes. That's chemistry, not a clinical finding. Which fraction matters depends on which trial you're trying to match.

The evidence, by use

Fatigue and wellbeing

The strongest single trial: 132 Chinese adults diagnosed with neurasthenia (a diagnosis centred on fatigue, used more in China than in the UK) were randomised to a reishi polysaccharide extract (Ganopoly, 1,800 mg three times a day) or placebo for 8 weeks. Fatigue and overall severity improved more with reishi: 51.6% were rated more than minimally improved, against 24.6% on placebo (Tang 2005). A small pilot trial in 48 women with breast cancer on hormone therapy reported less fatigue after 4 weeks of spore powder (Zhao 2012). Grade: mixed. Two small trials, both of specific products, neither repeated in a UK-type population.

Alongside cancer treatment

A Cochrane review found five randomised trials, all of poor quality. Reishi given alongside chemotherapy or radiotherapy was associated with better tumour response and quality of life, and with small rises in some immune-cell counts. No trial measured survival, and the reviewers found no case for reishi as a first-line treatment (Jin 2016). An uncontrolled study in mixed advanced cancers reported higher NK-cell activity after 12 weeks (Gao 2003). The same team's later study in advanced lung cancer found no significant change in NK activity overall (Gao 2005). Grade: mixed, poor-quality trials. If you have cancer, it belongs only in a conversation with your oncology team.

Cholesterol, blood sugar and blood pressure

The lab finding that triterpenes act on the statin pathway hasn't translated in people. A Cochrane review of trials in people with type 2 diabetes found no meaningful effect on HbA1c, total or LDL cholesterol, triglycerides or blood pressure. Adverse events were somewhat more common on reishi, though none were serious (Klupp 2015). Grade: tested, and no benefit shown.

Stress, cortisol and sleep

Reishi prolonged sleep in rats (Cui 2012), and there are animal studies on the stress response. There are no randomised trials in people for sleep or for cortisol. Grade: mechanistic and untested. I previously described the sleep effect as "mild but consistent" in practice. That was my impression, not evidence, and I've removed it.

The liver: both directions

Animal studies report protective effects on the liver, and a 10-day study in 10 healthy volunteers found no harmful changes in the markers measured (Wachtel-Galor 2004). Grade for "hepatoprotective": animal only. Set against that, there are case reports of liver injury with reishi powder:

Case reports can't tell you how common this is. Several involved other medicines too. But they rule out calling reishi "liver support" without a warning. I no longer suggest reishi for raised liver enzymes or a raised GGT. Those need a GP to find the cause.

How much: what the trials used
Reishi
Tested dose: 5.4 g a day of a reishi polysaccharide extract (Ganopoly), as 1,800 mg three times a day before meals, for 8 weeks, in adults with neurasthenia (Tang 2005). The cancer studies used the same product and amount for 12 weeks (Gao 2003; Gao 2005). Trials in type 2 diabetes used 1.4 to 3 g a day for 12 to 16 weeks, with no benefit (Klupp 2015). Most products on sale are not the extract that was tested.
Upper limit: no official upper limit (no EFSA, UK EVM or NHS figure). Long-term safety data are thin.
How long, and when to stop: the fatigue trial ran 8 weeks. If nothing has changed by then, stop. Stop at once, and see your GP, if you notice yellowing of the skin or eyes, dark urine, pale stools, itching or pain under the right ribs.
Check first if: you have liver disease or drink alcohol regularly; you take medicines that affect the liver, blood thinners, or immune-suppressing medicines; you are having cancer treatment; or you are pregnant or breastfeeding (no safety data).
Grade: mixed for fatigue (two small trials). Mixed and poor-quality alongside cancer treatment. No benefit for cholesterol, blood sugar or blood pressure. Untested for sleep and stress.

Choosing a product

If you decide to try it, the product matters, because most products on sale aren't what the trials used.

Product typePolysaccharidesTriterpenesMatches a trial?
Fruiting body, hot water + alcohol extractYesYesClosest to the general literature
Fruiting body, hot water onlyYesLowCloser to the polysaccharide trials
Mycelium grown on grainLower, plus grain starchLow or variableNo
Spore powderLowerHigherOne pilot trial (Zhao 2012)

Look for the species (Ganoderma lucidum), the part used (fruiting body or spores), the extraction method, and the beta-glucan and triterpene content per serving, plus a third-party test for heavy metals. I used to give minimum percentages here, but I can't point to a source for them, so I've taken them out. I also used to name two brands; I've removed those too. The same checklist is on the medicinal mushrooms guide.

Before you take it

If fatigue is the reason, the causes worth ruling out first, such as iron, thyroid, sleep and medicines, are ones your GP and a blood test can check. If liver enzymes or GGT are raised, see your GP before taking anything that acts on the liver, including reishi.

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Sources