The short answer
Side effects are uncommon and usually mild. The ones reported are stomach discomfort, headache and allergic reactions such as itching or a rash. Taking it with food and starting at a low dose helps with the stomach. Stop at once and get help if you have swelling of the face or throat, wheezing or difficulty breathing.
On this page
What side effects have been reported?
A 2025 systematic review of lion’s mane studies lists three possible side effects: stomach discomfort, headache and allergic reactions. The trials themselves reported very few problems. The first memory trial, which gave 3 g a day for 16 weeks, found no adverse effects on blood tests, and a trial giving 10 g a day for four weeks reported none either. The honest caveat is that small trials often record side effects loosely, so rare problems could be missed.
| Side effect | How often it is reported | What to do |
|---|---|---|
| Stomach upset, bloating, loose stools | Occasionally | Take it with food, split the dose, or lower it |
| Headache | Occasionally | Lower the dose; stop if it persists |
| Itching, rash or hives | Rarely | Stop taking it; see a pharmacist |
| Swelling of the lips, face or throat, wheezing, breathlessness | Not seen in trials, but possible with any allergy | Stop and call 999: these are signs of a serious allergic reaction |
Is lion’s mane hard on the liver or kidneys?
No harm to either has been shown. LiverTox, the US government database of drug and supplement liver injury, says lion’s mane has not been linked to raised liver enzymes or to any case of clinically apparent liver injury. Rat studies at very high doses found no liver or kidney damage. If you already have liver or kidney disease, ask your specialist before taking any supplement.
When should you stop?
Stop and talk to a pharmacist or GP if you get a rash, persistent stomach problems, or anything that started after you began taking it. Call 999 for swelling of the face, lips, tongue or throat, wheezing, or difficulty breathing or swallowing, which are signs of anaphylaxis.
You can report a suspected reaction through the MHRA’s Yellow Card scheme, which accepts reports about herbal and complementary products and helps spot rare problems that trials miss.
See who should avoid lion’s mane for pregnancy, medicines and other situations.
Common questions
Can lion's mane make you feel worse at first?
Some people report mild stomach upset or headache in the first days. These usually settle with food and a lower dose. There is no evidence for a 'detox' reaction, so if you feel unwell, stop.
Does lion's mane cause insomnia or vivid dreams?
Vivid dreams and trouble sleeping are mentioned online but have not been reported in the trials. If it affects your sleep, take it in the morning or stop.
Can you overdose on lion's mane?
No toxic dose has been found. Rats tolerated 2,000 mg per kg of body weight a day for 90 days, and one human trial gave 10 g a day for four weeks without problems. Taking more than the trial doses has no known benefit.
References
- Menon A et al. Benefits, side effects, and uses of Hericium erinaceus as a supplement: a systematic review. Frontiers in Nutrition, 2025.pubmed.ncbi.nlm.nih.gov
- LiverTox: clinical and research information on drug-induced liver injury. Lion's mane. US National Institute of Diabetes and Digestive and Kidney Diseases.ncbi.nlm.nih.gov
- Mori K et al. Improving effects of the mushroom Yamabushitake (Hericium erinaceus) on mild cognitive impairment: a double-blind placebo-controlled clinical trial. Phytotherapy Research, 2009.pubmed.ncbi.nlm.nih.gov Reported no adverse effects in laboratory tests over 16 weeks.
- Grozier CD et al. Four weeks of Hericium erinaceus supplementation does not impact markers of metabolic flexibility or cognition. International Journal of Exercise Science, 2022.pubmed.ncbi.nlm.nih.gov
- Mahadevan K et al. A toxicological assessment of Hericium erinaceus (lion's mane) and Trametes versicolor (turkey tail) mushroom powders. Frontiers in Toxicology, 2025.pubmed.ncbi.nlm.nih.gov
- NHS: anaphylaxis.nhs.uk
First published 3 November 2026. Spotted an error? Tell us and we'll correct it. Read our editorial policy.