Mushroom Coffee Side Effects: Documented, and Not

For most healthy adults, mushroom coffee has few side effects, and the ones people report are usually the coffee. The evidence at the rare end has grown, though. In 2025 the American College of Gastroenterology published four case abstracts of liver injury tied to reishi products, two of them mushroom coffee by name. A surgical journal reported a post-operative bleed blamed on a six-mushroom coffee. None of that makes the drink dangerous for the average person. All of it belongs on this page, with the complications the authors themselves list.

The scorecard: documented, reasoned, and not found

Start with the rest of the sachet

Before you blame a mushroom, read the other ingredients. Nearly all mushroom coffee is instant, and instant coffee upsets some stomachs on its own. Inulin and chicory, added as fibre or filler, cause bloating and gas in sensitive people at far smaller amounts than a cup holds. Sugar alcohols loosen stools, and so can MCT or coconut powder.

Then there is the caffeine, still the most active thing in the drink: 35 to 90 mg a serving by the brands' figures, against about 95 mg for a brewed 8 oz cup. Three servings and a jittery feeling is caffeine, and the FDA's 400 mg a day is the yardstick. None of this dismisses a real reaction. It is a reason to test by taking things out one at a time.

What each mushroom is known to do

Six species, six different cautions. The plainest public source is Memorial Sloan Kettering's About Herbs database, written for cancer patients and their doctors.

Reishi. Nausea, insomnia, dry mouth, constipation, itching and vertigo have been reported, plus case reports of liver injury from powdered reishi, one of them fatal. It can raise bleeding risk, may prolong the clotting tests INR, PT and APTT, and can enhance immune response, hence the flag for anyone on immunosuppressants. The one large survey of users covered 1,374 Chinese cancer patients; 9.1 percent reported any adverse effect, led by dry mouth at 5 percent.

Chaga. Talk to your provider if you take a blood thinner such as warfarin, because chaga may increase bleeding risk. Its three kidney cases get their own section below. In a test tube it had an additive blood-sugar-lowering effect, clinical significance unknown.

Lion's mane. Abdominal discomfort, nausea and a skin rash were reported in one clinical study; no drug interactions are listed. LiverTox calls it generally recognised as safe, with mild gut complaints usually in under 10 percent of trial subjects, and rates it E, unlikely to cause liver injury.

Cordyceps. No major side effects have been reported, with two cautions. It may lower blood sugar, which matters on insulin, and it may increase bleeding risk on warfarin; one daily user bled after a tooth extraction. LiverTox reports minimal or mild adverse events, notes its FDA GRAS (generally recognised as safe) status, and rates it E.

Shiitake. The odd one out, because its reaction is on the skin. Whip-like, linear red welts can appear after eating raw or even cooked shiitake, a pattern called shiitake or flagellate dermatitis. Prolonged use of the powder has also been followed by dermatitis, sun sensitivity and raised eosinophils, a type of white blood cell. Several mushroom coffees contain shiitake, so a whip-pattern rash after starting one is this.

Turkey tail. Dark stool and darkened fingernails, plus the one explicit pregnancy line in the set: until safety data exist, pregnant or breastfeeding women should avoid it. ^[6]

Can it hurt your liver?

Rarely, reversibly, and mostly in people who already had another reason for a fragile liver. Here is where that comes from.

The reference rating. The NIH's LiverTox entry on reishi (lingzhi), updated October 2024, says it is well tolerated and has not been linked to raised liver enzymes during treatment. It has been implicated in rare single cases of acute liver injury, most of which did not properly rule out other causes. Onset was typically 1 to 2 months after starting; recovery was rapid and complete within 1 to 3 months of stopping. Against worldwide use, LiverTox concludes that liver injury from reishi "must be extremely rare", and scores it D, a possible rare cause.

The case reports. At the American College of Gastroenterology's 2025 meeting, four abstracts described liver injury with reishi products, and two name mushroom coffee. A 2022 report from Malaysia is the only one with a formal causality score.

Read those together and you get a rare, real, reversible signal for reishi, found mostly in people whose livers had other problems. There is no equivalent signal for the other species. Dark urine, pale stool, yellowing skin or eyes, or pain under the right ribs after starting a mushroom coffee means stop and be seen.

Chaga and your kidneys

Chaga is the one species in the category with documented serious harm, and the reason is simple. It is loaded with oxalate, the compound behind most kidney stones: one Korean case analysis measured 14.2 g per 100 g. Three human cases are published, and the doses are the point.

Health Canada caps dried chaga at 3.6 g a day in licensed products. A coffee serving of chaga extract is a small fraction of any of those regimens. So the kidney cases are a reason for people with kidney disease or oxalate stones to pick a blend without chaga. They are not a reason for everyone else to worry. The chaga guide has the cases in full. ^[21]

Bleeding, and what to do before an operation

Three of the six species carry a bleeding caution at Memorial Sloan Kettering: reishi, chaga and cordyceps, each with advice to talk to a provider if you take warfarin. For reishi the effect shows up in clotting tests. This site's reishi review found platelet effects at around 3 g a day but not at 1.5 g, plus one published case of a raised INR on warfarin. Health Canada requires a blood-thinner caution on shiitake products too.

Then the case that put the coffee itself in a surgical journal. A 62-year-old man bled from a bowel join (an anastomosis) nine days after surgery and needed a procedure to seal the vessel. He had drunk mushroom coffee daily for two months beforehand, a blend labelled as cordyceps, lion's mane, reishi, shiitake, turkey tail and king trumpet. The authors ask surgeons to query mushroom coffees and adaptogen blends before an operation and to hold them like other drugs that act on platelets. One case, no platelet testing reported, and sensible advice: tell the anaesthetist, and stop beforehand.

The medication table

Pregnant or breastfeeding

Only the caffeine half of this question has an answer. Health Canada advises no more than 300 mg a day in pregnancy. A mushroom coffee serving at 35 to 90 mg sits well inside it. For the mushrooms, Health Canada's licensing monograph requires a label: ask a health care practitioner before use if you are pregnant or breastfeeding. That label goes on lion's mane, chaga, cordyceps and turkey tail products, and notably not on reishi, which carries only an allergy stop-use line.

Memorial Sloan Kettering's one explicit line is on turkey tail: it is not known whether it is safe. An earlier version of this page said reishi was commonly advised against in pregnancy; no authority we fetched says so. That is an absence of evidence, not a demonstrated harm, and a question for your own clinician. ^[6]

Allergy

These are mushrooms, and mushroom allergy exists. A 2024 review found anaphylaxis to edible mushrooms uncommon, with 28 cases in the literature, some cross-reactivity between species and no clear pattern to it. Health Canada's required line on reishi and shiitake products is to stop use if an allergic reaction occurs. If you react to mushrooms on a plate, skip them in a cup. ^{[20] [21]}

Why "it is just a mushroom" is the wrong instinct

Beta-glucans, the compounds these products are built around, are actively studied for immune activity. That is the reason the products exist, and the reason reishi carries an immunosuppressant caution. This site makes no claim about whether that activity does you any good. It is simply real enough to matter on the wrong medication. ^[22]

Who should not drink mushroom coffee without asking a clinician first

• Anyone on warfarin, a DOAC, clopidogrel or regular aspirin.
• Anyone on immunosuppressants, after a transplant or for autoimmune disease.
• Anyone on insulin or other blood-sugar-lowering drugs, for cordyceps and chaga blends.
• Anyone on long-term acetaminophen, with liver disease, or who drinks heavily, for reishi blends.
• Anyone with reduced kidney function or a history of oxalate stones, for chaga.
• Anyone with an operation booked: tell the surgeon, and stop beforehand.
• Anyone pregnant or breastfeeding.
• Anyone with a mushroom allergy should skip it altogether.

If you think it is disagreeing with you

1. Add up your caffeine for the day, at the serving size you actually use, against the FDA's 400 mg. ^[24]
2. Read the full ingredient list for inulin, chicory, sugar alcohols, MCT powder and added adaptogens. Any of them is a likelier cause of a digestive symptom than the mushrooms.
3. Try it without milk or creamer if the symptom is digestive.
4. Try a single-species product if you want to know which mushroom is responsible. A six-way blend makes that impossible.
5. Stop and see a clinician for anything that is not mild and brief: a rash, unusual bruising or bleeding, dark urine or yellowing, or a change in how much urine you pass.

The short version

For most healthy adults, mushroom coffee is one of the lower-risk things in a wellness aisle, and most reported side effects are the instant coffee, the inulin or the sweetener. The documented cautions are specific and dose-related: reishi and bleeding, reishi and a rare reversible liver injury, chaga and the kidneys at gram doses, cordyceps and blood sugar, shiitake and a rash. The 2025 case reports of liver injury with mushroom coffee are real, few, confounded and recovered. Nothing in the sources warns about blood pressure. Four groups should ask a clinician before starting, anyone with surgery booked should stop beforehand, and anyone whose urine darkens should stop today.