Lion's Mane Side Effects: What Studies Show and Who Should Avoid It

Lion's mane side effects are uncommon and usually mild. In human studies of lion's mane mushroom supplements, people mostly reported stomach discomfort, nausea, loose stools, headache and, less often, a skin rash. The one bad side effect that can be serious is a rare allergic reaction, so anyone who reacts to mushrooms should avoid it. This guide covers what the trials found, why some people say they feel "off" after starting lion's mane, possible interactions, and who should check with a clinician first.

It is educational, not medical advice.

Key Takeaways

• Usually well tolerated: a 2025 systematic review of the human and lab research found side effects were rarely reported and mostly mild.
• Most common complaints: stomach discomfort, nausea, diarrhea and headache. A skin rash was reported in one long trial.
• Rare but serious: allergic reactions, including one published case of a severe lung reaction in a man taking a lion's mane extract.
• Check first if you take medicine: lab and animal studies suggest lion's mane may affect platelets and blood sugar, so talk with your clinician if you take blood thinners or medicine that lowers blood sugar.
• Skip it if: you are allergic to mushrooms, or you are pregnant or breastfeeding, since there are no human safety studies in those groups.

Lion's Mane Side Effects at a Glance

Most people take lion's mane without any problems. Here is how the reported effects compare, and what to do about each:

Effect	How often	What to do
Stomach discomfort, nausea or loose stools	The most common complaints, usually mild	Take it with food, or lower the amount
Headache	Occasional	Drink water and try a lower amount
Skin rash	Reported in one long trial	Stop and check with your clinician
Allergic reaction	Rare	Stop and get medical help for swelling or trouble breathing
Effects with medicines	Seen in lab and animal studies	Check first if you take blood thinners or blood sugar medicine

For how lion's mane fits with other mushrooms, see lion's mane vs cordyceps and our guide to adaptogenic mushrooms.

Is Lion's Mane Safe? What the Research Shows

Lion's mane (Hericium erinaceus) is an edible mushroom that has been cooked and eaten in East Asia for centuries, and it is now one of the most popular functional mushrooms in supplements. You can read more about the mushroom itself on our lion's mane ingredient page.

The best summary of its safety so far is a 2025 systematic review that gathered five randomized controlled trials, three pilot trials, a cohort study, a case report and laboratory studies. The authors wrote that the human trials reported "minimal side effects," and that the side effects reported, although rare, were stomach discomfort, diarrhea, headaches and, in one study, a change in menstrual timing (Menon, 2025).

Here is what some of the key studies recorded about safety:

Study	Who and how much	What was reported
Mori, 2009 (16 weeks)	30 adults aged 50 to 80 with mild memory decline; 3 g a day of dried fruiting body powder	Laboratory tests showed no adverse effect.
Li, 2020 (49 weeks)	49 older adults with early memory decline; three 350 mg mycelium capsules a day	3 people on lion's mane and 1 on placebo stopped because of side effects: abdominal discomfort, nausea and skin rash (nausea on placebo). No other adverse events were reported.
Menon, 2025 (review)	Human trials and lab studies published 2000 to 2024	Side effects rarely reported; stomach discomfort, diarrhea, headache and allergic reactions listed.
Rat safety studies (2014 to 2022)	Daily doses up to 2 to 3 g per kg of body weight for 28 to 90 days	No treatment-related harm in blood tests, organ weights or tissue checks.

A 12-week Japanese trial of a fruiting body supplement in older adults also described oral lion's mane as safe (Saitsu, 2019). For more on what the trials measured beyond safety, see our guide to lion's mane for brain health.

The Most Common Lion's Mane Side Effects

When side effects do show up, they tend to be the kind you would expect from adding a concentrated food product to your routine:

• Stomach discomfort or bloating. The most frequently reported complaint across studies.
• Nausea. Reported in the 49-week capsule trial, where it was also reported in the placebo group.
• Loose stools or diarrhea. Listed in the 2025 review.
• Headache. Listed in the 2025 review from a short trial in healthy adults.
• Skin rash or itching. One of the reasons people left the 49-week trial, and a possible sign of allergy (see below).

Stomach effects are often easier to manage by taking lion's mane with food and starting with a smaller amount. If a rash, swelling or itching appears, stop taking it.

Rare but Serious: Allergic Reactions

Allergy is the one lion's mane side effect that can be serious. Two published reports stand out:

• A severe lung reaction. In 2003, doctors in Japan described a 63-year-old man who developed acute respiratory failure after taking a lion's mane extract sold as a diet food. Lab testing showed a strong immune reaction to the extract, and he recovered in intensive care (Nakatsugawa, 2003). The 2025 review called it the only report of its kind.
• Skin reactions from handling. A 1999 report described allergic contact dermatitis in a person who handled the fresh mushroom at work (Maes, 1999).

Stop taking lion's mane and get medical help right away if you notice wheezing, shortness of breath, swelling of the face or throat, or hives. People with a known mushroom or mold allergy should not take it.

Why Some People Say They Feel "Off" on Lion's Mane

Online forums include reports of people feeling restless, on edge, low or foggy, or sleeping poorly, after starting lion's mane. These effects were not among those listed in the controlled trials above, and individual reports cannot show cause and effect. Still, they are worth taking seriously if they happen to you. We look at both positive and negative user experiences in our guide to lion's mane and focus.

A few practical points if you feel different after starting:

• Change one thing at a time. If you started lion's mane alongside coffee, other nootropics or a new routine, it is hard to know which one is responsible.
• Check the product. Supplements vary widely: some use the fruiting body, others use mycelium grown on grain, and extract strengths differ. Our guide to mushroom extracts vs powders explains the differences.
• Take it earlier in the day. If sleep changes, move your dose to the morning.
• Stop if it persists. Effects that do not settle, or that affect your mood, are a reason to stop and talk with a clinician.

Is Lion's Mane Hard on the Liver?

The published safety studies do not point to liver harm. In the 16-week human trial, laboratory tests showed no adverse effect (Mori, 2009). In rats, 28-day and 90-day studies of lion's mane mycelium and extracts found no treatment-related changes in blood chemistry or organ tissue, at doses far above typical human intake (Li, 2014; Lee, 2019; Chen, 2022). If you have a liver condition, ask your clinician before adding any new supplement.

Possible Interactions

The cautions below come from laboratory and animal research. They are reasons to check with a clinician, not proof of a problem:

• Blood thinners and anti-platelet medicine. In a laboratory study, hericenone B, a compound from lion's mane, blocked collagen-triggered clumping of rabbit and human platelets (Mori, 2010). In theory this could add to the effect of medicines that slow clotting. For the same reason, tell your surgeon if you take lion's mane before a procedure.
• Medicine that lowers blood sugar. Lion's mane extracts lowered blood glucose in rats with diabetes (Liang, 2013). If you take glucose-lowering medicine, ask your clinician and watch your readings.

Lion's mane is often combined with other functional mushrooms such as cordyceps and reishi. Our comparison of lion's mane vs cordyceps covers how people take them together. For reishi on its own, see our reishi mushroom (Ganoderma lucidum) page. Some people also pair lion's mane with creatine; our guide to creatine and lion's mane covers how to take the two together.

Who Should Avoid Lion's Mane or Check First

• People allergic to mushrooms or mold: avoid it.
• Anyone pregnant or breastfeeding: skip it unless your clinician advises otherwise. A rat study found no harm to developing offspring at high doses (Li, 2018), but there are no human studies.
• People taking blood thinners or blood sugar medicine: check with your clinician first.
• Anyone who has had a breathing reaction to a supplement or mushroom: talk with your clinician first, given the rare lung reaction described above.
• Anyone scheduled for surgery: tell your care team about every supplement you take.

Form and amount matter too; our guide to lion's mane powder, capsules and extract explains what to check on a label.

How to Lower Your Risk of Side Effects

1. Start low. Consider half a serving for the first few days, then move to the serving on the label if you feel fine.
2. Take it with food if your stomach is sensitive.
3. Add one new supplement at a time, so you can tell what is helping and what is not. Our smart stacking guide explains how to introduce and cycle supplements.
4. Choose full disclosure. Look for a label that names the part of the mushroom used (fruiting body or mycelium), the extract ratio, the dose of every ingredient and third-party tested ingredients.
5. Stop and reassess if anything new appears, especially a rash or breathing changes.

Is It Safe to Take Lion's Mane Every Day?

Most human trials gave lion's mane every day, for periods from 4 weeks to 49 weeks, and reported few side effects. Those studies run up to about a year, so it is sensible to check in with yourself every few months and take a break if you are unsure it is still worth taking. For dose ranges, see our guide to lion's mane dosage, and for women over 40 and 50, see lion's mane for women.

How Lion's Mane Is Used in Our Formulas

We use an 8:1 lion's mane fruiting body extract, made with third-party tested ingredients and listed with its exact dose:

• Clarity Capsules: 250 mg of lion's mane 8:1 fruiting body extract per 2-capsule serving, with epimedium, maca, bacopa, rhodiola and huperzine A.
• Forage: 200 mg of lion's mane 8:1 fruiting body extract per 2-capsule serving, with cordyceps, reishi, chaga, maitake, turkey tail, shiitake, Himalayan shilajit and 100 mg of ashwagandha root extract.

Because these formulas combine several ingredients, read each one on the label against the cautions above, and check our guide to adaptogenic mushrooms for the other mushrooms in Forage. For the bigger picture on supporting focus and memory, visit our cognitive health and mental clarity hub. Our Mushroom Cacao pairs lion's mane with cordyceps in a mushroom hot chocolate.

Frequently Asked Questions

Why do I feel weird after taking lion's mane?

Some people report feeling restless, foggy or low after starting lion's mane. These reports come from personal accounts rather than trials, and other changes made at the same time can be the cause. If the feeling persists, stop taking it and speak with a clinician.

Is it bad to take lion's mane every day?

Human trials used daily doses for 4 to 49 weeks and reported few side effects, mostly mild stomach complaints.

Who should not take lion's mane?

People with a mushroom or mold allergy should avoid it. Anyone pregnant or breastfeeding, or taking blood thinners or blood sugar medicine should check with a clinician first.

What should you not mix lion's mane with?

Lab and animal studies suggest caution with medicines that slow blood clotting and medicines that lower blood sugar. Ask your clinician before combining lion's mane with either.

Can lion's mane make you feel anxious?

The controlled trials did not list this as a side effect, but some users describe feeling on edge. If you notice it, take a break and reintroduce at a lower amount, or stop.

Does lion's mane affect the liver?

The published human and animal safety studies did not find liver harm. People with liver conditions should still ask a clinician before starting.

Can lion's mane cause an allergic reaction?

Yes, rarely. One published case described a severe lung reaction to a lion's mane extract, and handling the fresh mushroom has caused skin reactions. Stop and seek care for wheezing, swelling or hives.

Does lion's mane affect sleep?

Sleep problems were not among the side effects listed in the trials. If you notice a change, take lion's mane in the morning instead of later in the day.

Are there bad side effects of lion's mane?

Serious side effects are rare. The 2025 systematic review found that side effects were rarely reported in human trials and were mostly mild, such as stomach discomfort, diarrhea and headache. The serious risk on record is an allergic reaction, including one published case of a severe lung reaction to a lion's mane extract. Avoid it if you have a mushroom or mold allergy, and get medical help for wheezing, swelling or hives.

Can lion's mane upset your stomach?

It can. Stomach discomfort or bloating is the most frequently reported complaint across studies, and nausea and loose stools have also been listed. These effects are usually mild. Taking lion's mane with food can make it easier to tolerate. If stomach upset continues, stop taking it and talk with a clinician.

Does lion's mane cause headaches?

Headache is listed among the side effects in the 2025 systematic review, from a short trial in healthy adults, but it was uncommon. If you get headaches after starting lion's mane, check whether anything else changed at the same time, such as caffeine or another new supplement. If they continue, stop taking it and speak with a clinician.

Can lion's mane affect your period?

The 2025 systematic review noted a change in menstrual timing in one study, among the rare side effects it listed. If your cycle changes after you start lion's mane, keep a note of it and talk with your clinician, especially if you are trying to conceive. If you are pregnant or breastfeeding, skip lion's mane unless your clinician advises otherwise.

Is lion's mane mushroom safe to eat?

Lion's mane is an edible mushroom that has been cooked and eaten in East Asia for centuries. The allergy cautions apply to the food as well as to supplements: people with a mushroom or mold allergy should avoid it, and one published report described allergic skin reactions in a person who handled the fresh mushroom at work.

How much lion's mane is safe per day?

Human trials gave it daily for 4 to 49 weeks with few side effects. Follow your product label: our Forage has 200 mg, Clarity Capsules 250 mg and Mushroom Cacao 500 mg of lion's mane 8:1 fruiting body extract per serving.

Is lion's mane in hot chocolate or coffee safe?

The same cautions apply in a drink as in a capsule. In a mushroom hot chocolate, the cocoa also adds a little caffeine and theobromine; see our guide to mushroom hot chocolate.

Sources

• Menon A, et al. Benefits, side effects, and uses of Hericium erinaceus as a supplement: a systematic review. Front Nutr. 2025. PubMed 40959699
• Mori K, et al. Improving effects of the mushroom Yamabushitake (Hericium erinaceus) on mild cognitive impairment: a double-blind placebo-controlled clinical trial. Phytother Res. 2009. PubMed 18844328
• Li IC, et al. Prevention of early Alzheimer's disease by erinacine A-enriched Hericium erinaceus mycelia: pilot double-blind placebo-controlled study. Front Aging Neurosci. 2020. PubMed 32581767
• Saitsu Y, et al. Improvement of cognitive functions by oral intake of Hericium erinaceus. Biomed Res. 2019. PubMed 31413233
• Nakatsugawa M, et al. Hericium erinaceum (yamabushitake) extract-induced acute respiratory distress syndrome monitored by serum surfactant proteins. Intern Med. 2003. PubMed 14714963
• Maes MF, et al. Occupational allergic contact dermatitis from the mushroom White Pom Pom (Hericium erinaceum). Contact Dermatitis. 1999. PubMed 10344494
• Mori K, et al. Inhibitory effect of hericenone B from Hericium erinaceus on collagen-induced platelet aggregation. Phytomedicine. 2010. PubMed 20637576
• Liang B, et al. Antihyperglycemic and antihyperlipidemic activities of aqueous extract of Hericium erinaceus in experimental diabetic rats. BMC Complement Altern Med. 2013. PubMed 24090482
• Li IC, et al. Evaluation of the toxicological safety of erinacine A-enriched Hericium erinaceus in a 28-day oral feeding study in Sprague-Dawley rats. Food Chem Toxicol. 2014. PubMed 24810469
• Lee LY, et al. Thirteen-week oral toxicity evaluation of erinacine A-enriched lion's mane medicinal mushroom mycelia in Sprague-Dawley rats. Int J Med Mushrooms. 2019. PubMed 31002635
• Chen SN, et al. Subchronic toxicity and genotoxicity studies of Hericium erinaceus beta-glucan extract preparation. Curr Res Toxicol. 2022. PubMed 35341120
• Li IC, et al. Acute and developmental toxicity assessment of erincine A-enriched Hericium erinaceus mycelia in Sprague-Dawley rats. Drug Chem Toxicol. 2018. PubMed 29359595

These statements have not been evaluated by the Food and Drug Administration. This content is for education and is not medical advice. Our products are not intended to diagnose, treat, cure or prevent any disease. Talk with a healthcare provider before starting a new supplement if you are pregnant, breastfeeding or taking medication.