Lion's mane is a food as well as a supplement, and it has a reputation for being gentle. That reputation is mostly right, but "gentle" isn't the same as "studied", so this guide goes through what human trials actually reported, what the animal tests show, and what hasn't been tested. For what lion's mane is and how to choose a product, see our lion's mane guide.
Common Lion's Mane Side Effects
A 2025 systematic review of lion's mane (Hericium erinaceus) as a supplement included five randomized trials, three pilot trials, laboratory studies, one cohort study and one case report. It concluded that potential side effects, although commonly unreported, include stomach discomfort, headache and allergic reactions Preliminary.
| Side effect | What's known |
|---|---|
| Stomach discomfort, nausea | The most commonly reported; one trial had dropouts for it |
| Skin rash or itching | Reported in a 49-week trial; allergic reactions are listed in the review |
| Headache | Listed in the review |
| Mushroom allergy reaction | The clearest reason to avoid it |
What the Longest Trial Found
In a 49-week double-blind trial of people with mild Alzheimer's disease, patients took three 350mg capsules a day of erinacine A-enriched lion's mane mycelia (5mg per gram of erinacine A) or a placebo. Except for four participants who dropped out because of abdominal discomfort, nausea and skin rash, no other adverse events were reported, and the authors concluded it was safe and well tolerated Preliminary. That is a small pilot in older adults with a specific mycelium product, so it can't speak for every capsule or every person.
Is Lion's Mane Safe Long Term?
For healthy adults taking it daily for months or years, nobody knows. Trials in healthy younger adults were short: a single dose, or 28 days. Animal safety studies are reassuring but aren't human evidence: a toxicology study of lion's mane powder (mycelium and fruiting body grown on oats) found no acute or subchronic toxicity or genotoxicity in rats at doses up to 2,000mg/kg of body weight a day.
What About Allergy?
Allergic reactions are listed among the potential side effects in the 2025 review, and rash was among the reasons for dropout in the long trial. If you're allergic to mushrooms or have had reactions to supplements, avoid lion's mane. If you develop hives, swelling, wheeze or trouble breathing after taking it, stop and seek medical help.
Supplement Mixes: A Safety Footnote
A 2025 case report described a woman with metastatic colorectal cancer who developed grade 3 liver cytolysis and cholestasis while taking a supplement containing lion's mane and Agaricus blazei Murrill powder. Her liver function improved after stopping, and the authors attributed it mainly to Agaricus blazei. It's a reminder that mushroom blends make it impossible to know which ingredient is responsible, and that anyone being treated for cancer should tell their care team about every supplement.
How Much Lion's Mane Do Trials Use?
| Trial | Dose | Result |
|---|---|---|
| 41 healthy adults aged 18–45, 28 days | 1.8g of lion's mane a day | Faster Stroop task performance 60 minutes after a single dose; a trend toward lower stress at 28 days |
| 18 healthy adults aged 18–35, single dose | 3g of a 10:1 fruiting body extract | No significant effect on overall cognition or mood; one task (pegboard) improved |
| Adults with mild Alzheimer's disease, 49 weeks | 1,050mg a day of erinacine A-enriched mycelia | Better cognitive-screening and daily-living scores than placebo |
| 30 women, 4 weeks | Lion's mane cookies (dose not given in the abstract) | Lower depression and "indefinite complaints" scores in the lion's mane group |
There's no agreed dose, and trials used different forms, so the label's suggested serving is a more reliable guide than comparing milligrams across brands (see our guide on fruiting body versus mycelium). The 2025 review pooled an increase of 1.17 points on the Mini-Mental State Examination from one randomized and one pilot trial, which shows the effect is modest.
Who Should Check With a Doctor First
- Mushroom allergy or past supplement reactions: avoid it.
- Medication: particularly diabetes medication or blood thinners; ask a pharmacist, since interactions haven't been studied in people.
- Pregnancy and breastfeeding: there are no safety trials, so ask your doctor or midwife.
- Surgery planned: tell your surgical team.
- Cancer treatment: tell your oncology team about any supplement, including mushroom blends.
To compare other brain-focused supplements, see Lion's Mane vs. Bacopa.
