Reishi mushroom: what the evidence shows, side effects and who should avoid it

What is reishi mushroom?

Reishi (Ganoderma lucidum) is a wood-growing mushroom with a glossy red-brown cap. In China it’s called lingzhi, and one of its folk names is “mushroom of immortality”. It has a long history in traditional medicine in China, Japan and Korea.

You can eat the whole mushroom, but powders and extracts are used far more often. Reishi is sold as capsules, tablets, extracts, powders and tea, and there’s also a separate spore powder. Its active compounds are thought to be polysaccharides (including beta-glucans) and triterpenes.

Reishi benefits: what the research shows

In cell and animal studies, reishi extracts affected immune cells, protected the liver and kidneys and slowed the growth of tumour cells. In people, these results have largely not held up. According to the MSD Manual, the studies are few, many are small and poor quality, and some contradict others.

A 2025 meta-analysis pooled 17 randomised trials. It found a small fall in body mass index and heart rate, but no effect on blood pressure, blood sugar, cholesterol, inflammation or liver enzymes. Its authors rated the certainty of the evidence as very low for every outcome.

Before you buy, bear in mind:

• there are no strong trials with a clear result for reishi;
• products vary widely: mushroom powder, extract, spore powder;
• no health claim for reishi has been authorised in the UK or EU;
• the MSD Manual concludes that most people have no compelling reason to take it.

Reishi side effects and risks

Liver

The most serious risk is liver injury. A first case was described in Hong Kong in 2004, and a second in Thailand in 2005 ended in death from fulminant hepatitis. Both patients had drunk boiled reishi before without problems, and both were also taking other medicines. Liver damage developed 1–2 months after they switched to reishi powder.

Memorial Sloan Kettering (MSK), a US cancer centre, lists further cases: hypereosinophilia (too many of one type of white blood cell) with liver nodules, and acute liver injury in a man who also drank alcohol. Results usually returned to normal after stopping the mushroom. The MSD Manual says extract taken for up to a year might be safe, but powder taken for over a month could damage the liver.

Bleeding

MSK warns that reishi may raise the risk of bleeding with anticoagulants and antiplatelet medicines. Its extracts may prolong clotting tests such as INR, PT and APTT. Yet in a trial of 20 healthy volunteers, 1.5 g a day for 4 weeks didn’t change clotting. There’s no data in people already on blood thinners, so it’s not worth the risk.

Blood pressure

According to the MSD Manual, reishi might lower blood pressure, so with blood pressure medicines it could make it too low. In controlled trials, blood pressure didn’t change on reishi. So the risk is mostly theoretical, but if your blood pressure is low or you take tablets for it, talk to your GP first.

Other side effects

Trials and case reports describe:

• nausea, upset stomach, diarrhoea or constipation;
• insomnia, dizziness, headache;
• dry mouth, itching and rash;
• nosebleeds.

Don’t take reishi if:

• you’re pregnant or breastfeeding: its safety hasn’t been studied;
• you have low blood pressure or a bleeding disorder, including a low platelet count;
• you have surgery coming up;
• you have liver disease, given the reported cases of liver injury.

Talk to your GP or pharmacist first if you take:

• warfarin, clopidogrel, heparin, or regular ibuprofen or naproxen;
• blood pressure medicines;
• immunosuppressants, because reishi may boost the immune response;
• chemotherapy, as it may interact with some cancer medicines.

Reishi spore powder can raise the tumour marker CA72-4 in blood tests. Before any tumour marker test, tell your doctor you take it.

Dark urine, yellowing of the skin or eyes, itching, unexplained bruising or bleeding gums are reasons to stop at once and see a doctor. Taking several supplements and medicines? Check our vitamin compatibility chart.

How to take reishi

There’s no official dose. Trials used:

Powder, extract or spores?

iHerb sells three kinds of product, and their risks differ:

• Mushroom powder is dried, ground reishi. Reported cases of liver injury were linked to powder.
• Extract contains compounds drawn out of the mushroom with water or alcohol. It’s easier to dose, and a good label states the beta-glucan or triterpene content.
• Spore powder is made from the mushroom’s spores rather than the cap. It can raise the CA72-4 tumour marker and showed no benefit in a pilot study in Alzheimer’s disease.

If your GP agrees:

1. Choose an extract rather than raw mushroom powder, since the liver cases mostly involved powder.
2. Don’t exceed the label dose. If you do choose raw powder, don’t take it for longer than a month, as the MSD Manual advises.
3. Don’t combine it with alcohol.
4. If you have surgery coming up, stop in good time and tell your surgeon, who will say how far ahead.

Better-studied options for immunity

Supplements “for immunity” mainly help when you’re short of something. Start with what’s better studied:

• vitamin D: the NHS advises 10 mcg a day in autumn and winter;
• zinc, if your diet is low in it;
• sleep, physical activity and the vaccines offered to you on the NHS.

You’ll find more options in our immunity section. Not sure what you need? Try our vitamin check. For another popular mushroom, read about lion’s mane.

How to choose reishi on iHerb

Open the product page and find what it’s made from. Then pick that line below:

1. Check the lists above for medicines and conditions that rule it out.
2. Look for Ganoderma lucidum and “fruiting body extract” on the label.
3. Prefer products that state beta-glucans or triterpenes rather than only “polysaccharides”.
4. Avoid raw mushroom powder for long-term use.
5. Pick a single-ingredient product rather than a mushroom blend, so you know what caused any reaction.
6. Look for independent quality testing (USP, NSF or similar seals).