Reishi side effects: What is known, and who should be careful?
Short answer: Reishi is generally well tolerated in studies. In a review of 5 studies with a total of 398 participants who took 1.4 to 3 grams of reishi per day for 12 to 16 weeks, side effects were not significantly more common than with a placebo and were not serious (Klupp et al., 2015). The effects reported were mostly mild symptoms, such as nausea or difficulty sleeping. If you are pregnant, have liver problems, are allergic to mushrooms, or take medication, consult your doctor or pharmacist first.
Last updated: October 30, 2026 · Written by Florian Fermin
"How many capsules can I take per day?" We get this question often, and it really points to another question: can taking more also be harmful? Online, you can find long lists of reishi side effects, often without sources. That's why this page only covers what has been reported in research, as well as what we still don't know.
What side effects of reishi have been reported in research?
Controlled studies of reishi report few and mostly mild side effects. One Cochrane review mentions nausea and insomnia in one study. A second Cochrane review found no serious side effects with 1.4 to 3 grams of reishi per day for 12 to 16 weeks.
Reishi is called gesteelde lakzwam in Dutch, reishi or lingzhi in English, and Ganoderma lucidum in Latin. It is a hard, woody mushroom that has been used in Asia for centuries. Learn more about its origins and compounds in our article about the reishi mushroom.
In the review by Klupp and colleagues, participants taking reishi were 1.67 times as likely to experience a side effect as those taking a placebo. The confidence interval ranged from 0.86 to 3.24, so the difference could also be due to chance. The studies were small and only adults from a specific group took part, so the results cannot simply be applied to everyone (Klupp et al., 2015).
The review by Jin and colleagues found that only one of five studies reported side effects: nausea and insomnia (Jin et al., 2016). A U.S. NIH database on the safety of medicines states that short clinical studies generally report few or no side effects (NIH, 2024).
How common are reishi side effects, and how strong is the evidence?
How often reishi causes side effects is not well known. The studies we found lasted 4 to 16 weeks, were small, and did not always record side effects. What is known is listed in the table below, along with the source and strength of the evidence.
| Possible side effect or point to note | What was reported | Type of evidence | Source |
|---|---|---|---|
| Mild symptoms (nausea, difficulty sleeping) | In one study, not serious | Randomized studies, summarized in a review | Jin et al., 2016 |
| Side effects in general | 1.67 times as often as with placebo, not significant, none serious | 5 studies, 398 participants | Klupp et al., 2015 |
| Liver | Reported very rarely, often alongside other substances or alcohol | Isolated reports | NIH, 2024 |
| Effect on blood clotting | No change at 1.5 g per day for 4 weeks in healthy people | Randomized study, 40 participants | Kwok et al., 2005 |
| Allergy to spores | Skin reactions to reishi spore extract in people with respiratory allergies | Skin tests, not ingestion | Singh et al., 1995 |
What should you keep in mind if you have liver problems?
Only a few isolated reports are known about reishi and the liver. They are often poorly documented and sometimes involved other substances or alcohol. The NIH database describes this as very rare (NIH, 2024). There is no good research on reishi in people with liver problems.
If you have liver problems or drink a lot of alcohol, check with your doctor before taking reishi.
Does reishi affect blood clotting, and what does that mean if you take blood thinners?
In healthy people, reishi does not appear to affect blood clotting. In a randomized study, 40 healthy volunteers received 1.5 grams of reishi or a placebo per day for 4 weeks, and all clotting values remained normal. This has not been studied in people who take blood thinners.
The study was conducted because laboratory research had suggested that reishi might inhibit platelet function. This was not observed in the 20 participants who took reishi (Kwok et al., 2005).
If you take blood thinners or have surgery coming up, simply let your doctor or pharmacist know that you're taking reishi. The study doesn't say anything about combining it with medication.
Who should take extra care with reishi, even at a normal dose?
Extra caution applies to people with an allergy to mushrooms or molds, people with liver problems, pregnant women and women who are breastfeeding, and anyone taking medication. There isn't enough safety data for these groups. Check with your doctor or pharmacist first.
- Allergy. In India, 28% of 172 people with respiratory allergies reacted to a skin test with reishi spores (Singh et al., 1995). This concerns inhaled spores, not a supplement, but if you're allergic to mushrooms, don't start taking it without checking first.
- Medications. There are no good studies on interactions between reishi and medications. If you take blood thinners or other medications, check with your doctor or pharmacist.
- Pregnancy and breastfeeding. We found no studies on reishi in pregnant women or during breastfeeding. Without data, the advice is: don't start taking it on your own.
- Children. We also found no studies on reishi in children.
Does it matter whether you take reishi as a powder, extract, or tea?
The form affects how much you take in. An extract is concentrated, so the dosage on the label is even more important than for powder. Follow the daily dosage on the label for every form.
Quality also matters. Lead, cadmium, and mercury have been measured in reishi grown on wood, while no cadmium or mercury was found in the wild samples tested (Wachtel-Galor et al., 2011). So ask for a certificate of analysis. Our article about a CoA for a mushroom supplement explains how to read one.
If you combine several products containing reishi, add the amounts together. You can read about the differences between the forms and how much reishi you get from each in reishi powder, capsules, or extract.
What should you do if you think you're experiencing side effects from reishi?
Stop taking reishi and contact your doctor if your symptoms don't go away. Bring the product with you, or note its name, the dosage, and how long you've been using it. If your skin or eyes turn yellow, don't wait; call your doctor the same day.
I would always start with the lowest dosage on the label. That way, you can tell sooner whether you tolerate it well, and you won't take more than you need.
Do you use other mushrooms too? We wrote a separate article about the side effects of lion's mane: side effects of lion's mane.
Summary in 3 points
- In studies lasting 4 to 16 weeks, with 1.4 to 3 grams of reishi per day, few side effects were reported, and they were mostly mild, such as nausea and poor sleep.
- Only a few isolated reports are known regarding the liver. If you have liver problems, consult your doctor first.
- For pregnancy, breastfeeding, liver problems, a mushroom allergy, or medication use, safety data are lacking: consult your doctor or pharmacist first.
Frequently asked questions
Is reishi safe to take every day?
No serious side effects were observed in studies lasting up to 16 weeks, with doses of 1.4 to 3 grams per day. Little is known about use over several years. Follow the dosage on the label.
Can you take reishi if you use blood thinners?
This has not been studied. Blood clotting did not change in healthy people, but that tells us nothing about combining it with medication. So consult your doctor or pharmacist first.
Can reishi cause poor sleep or nausea?
Nausea and insomnia were reported in one study (Jin et al., 2016). How often this occurs is not known.
Can you use reishi if you have liver problems?
There is no reliable research on this. Regarding the liver, only a few isolated reports are known, sometimes in combination with other substances or alcohol. So consult your doctor first.
Can you use reishi during pregnancy?
There are no studies on reishi in pregnant women or during breastfeeding. So don't start taking it on your own, and consult your midwife, doctor or pharmacist.
Sources
- Klupp NL, Chang D, Hawke F, Kiat H, Cao H, Grant SJ, Bensoussan A (2015). Cochrane review of Ganoderma lucidum in adults, randomized trials. Cochrane Database of Systematic Reviews, 2015(2), CD007259. Europe PMC 25686270
- Jin X, Ruiz Beguerie J, Sze DM, Chan GC (2016). Cochrane review of Ganoderma lucidum (reishi), randomized trials. Cochrane Database of Systematic Reviews, 4(4), CD007731. Europe PMC 27045603
- National Institutes of Health (NIH). Lingzhi, Reishi. NCBI Bookshelf, updated October 5, 2024. NCBI Bookshelf NBK609014
- Kwok Y, Ng KFJ, Li CCF, Lam CCK, Man RYK (2005). A prospective, randomized, double-blind, placebo-controlled study of the platelet and global hemostatic effects of Ganoderma lucidum (Ling-Zhi) in healthy volunteers. Anesthesia and Analgesia, 101(2), 423-426. Europe PMC 16037156
- Singh AB, Gupta SK, Pereira BM, Prakash D (1995). Skin prick test study of sensitivity to Ganoderma lucidum spores in India. Clinical and Experimental Allergy, 25(5), 440-447. Europe PMC 7553247
- Wachtel-Galor S, Yuen J, Buswell JA, Benzie IFF. Ganoderma lucidum (Lingzhi or Reishi). In: Benzie IFF, Wachtel-Galor S, editors. 2nd ed. Boca Raton (FL): CRC Press/Taylor & Francis; 2011. Chapter 9. NCBI Bookshelf NBK92757
To find out which forms of reishi we sell, visit the buy reishi page.
This article is for informational purposes and is not medical advice. Dietary supplements are not a substitute for a varied and balanced diet and a healthy lifestyle. If in doubt, during pregnancy, or when taking medication, consult your doctor or pharmacist.
Reishi from GOYU
Available as powder, capsules (without fillers) and extract capsules (20:1).
