A hot-water reishi extract inhibited ADP-induced platelet aggregation more strongly than 140 µmol/L of aspirin in one laboratory screen — and left prothrombin time and INR completely unchanged. That combination is the problem in a sentence. The blood test your surgeon runs before an operation is built to catch clotting-factor problems, and it is blind to the mechanism mushroom extracts appear to act through.
The American Society of Anesthesiologists and the American Association of Nurse Anesthetists recommend stopping herbal medications one to two weeks before elective surgery. Mushroom extracts are rarely named in that advice, but an in vitro screen of eight edible species found Ganoderma lucidum (reishi) inhibited both ADP- and arachidonic-acid-induced platelet aggregation, exceeding 140 µmol/L aspirin in the ADP test, while none of the eight extracts altered prothrombin time, prothrombin ratio or INR. A published case report documents INR elevation when maitake extract was combined with warfarin. Between 50% and 70% of surgical patients do not tell anyone they take supplements, and most do not stop them. The safe default is to stop mushroom supplements two weeks before an operation and to name them, by species and dose, at the pre-assessment.
This is not a reason to be frightened of mushrooms. It is a reason to treat them as medication in the one two-week window where the distinction actually matters.
What the Professional Guidance Actually Says
It says stop. Both the ASA and the AANA recommend discontinuing herbal medications one to two weeks before elective surgical procedures, on the grounds that these products interact with anaesthetic agents across the coagulation, cardiovascular, central nervous, pulmonary, renal and endocrine systems.
The compliance picture is poor. In the review that summarises this guidance, between 50% and 70% of surgical patients fail to disclose herbal medication use to their physicians, and most of those who do disclose it do not stop.
Mushroom supplements slip through this even more easily than herbs, because people file them mentally as food. A dried mushroom in a stew is food. A concentrated extract taken daily at a fixed dose is not, and the pre-operative questionnaire is exactly where that distinction should be made out loud.
Why Reishi Is the One to Watch
Because of a specific laboratory finding. Poniedziałek's 2019 screen tested hot-water extracts of eight edible mushroom species against human platelets and compared them directly with acetylsalicylic acid.
Ganoderma lucidum showed a dual antiplatelet effect, inhibiting aggregation induced by both ADP and arachidonic acid. In the ADP test the response exceeded that of 140 µmol/L aspirin. The same extract was also cytotoxic to platelets and leukocytes in that system, which the authors flag as a caution rather than a benefit.
Earlier mechanistic work points the same way: ganodermic acid S has been shown to act on thromboxane A2 signalling pathways in human platelets and to potentiate prostaglandin E1-induced cyclic AMP elevation. Two independent lines of evidence, both pointing at platelet function.
None of this is a clinical bleeding study, and it should not be overstated. It is enough to justify a two-week pause before someone cuts you.
The Test That Would Not Catch It
Routine pre-operative blood work measures prothrombin time, prothrombin ratio and INR. Those tests report on the clotting-factor cascade — the system warfarin acts on.
Platelet aggregation is a different mechanism, and it is not routinely tested before surgery. The same study that found reishi's antiplatelet effect found that none of the eight extracts changed any of the three coagulation parameters, which is precisely the pattern aspirin produces: normal INR, impaired platelets.
So a patient taking a concentrated reishi extract can present a completely reassuring clotting panel. The panel is not wrong; it is measuring something else.
There is a second, uncomfortable implication. The antiplatelet effect in that screen correlated positively with polysaccharide and ergosterol content — meaning the better-made, more concentrated extract is the one more likely to produce it. Quality does not equal safety here; it runs the other way.
Maitake, Warfarin and the INR Exception
One documented interaction does show up on standard testing. Hanselin and colleagues published a case of INR elevation in a patient taking maitake extract alongside warfarin, in Annals of Pharmacotherapy in 2010.
That is a single case report, which is the weakest form of clinical evidence and also exactly the form that first identifies real interactions. For anyone on warfarin heading into a procedure, it is the reason maitake deserves an explicit mention rather than a general one — our maitake interactions article covers the anticoagulant question in more detail.
Amanita Muscaria Is a Different Question Entirely
It is not a bleeding risk; it is an anaesthetic one. Muscimol, the compound responsible for most of Amanita muscaria's effects, is a GABA-A receptor agonist — and GABA-A is the receptor family that propofol, benzodiazepines and the volatile anaesthetic agents all act on.
No study has measured what happens when the two are combined, and nobody should be finding out on an operating table. The honest position is that this is an untested pharmacological overlap at an important receptor, which makes full disclosure to the anaesthetist essential rather than optional. Our Amanita muscaria interactions article sets out what is documented.
Species by Species
| Species | Concern | Evidence level | Stop before surgery? |
|---|---|---|---|
| Reishi | Platelet aggregation inhibition | In vitro, plus mechanistic work on ganodermic acid S | Yes — two weeks |
| Maitake | INR elevation with warfarin | Published case report | Yes — two weeks |
| Amanita muscaria | GABA-A overlap with anaesthetic agents | Mechanistic; untested in combination | Yes, and disclose explicitly |
| Shiitake, lion's mane | Screened; no notable antiplatelet effect | In vitro screen of eight species | Stop anyway, by general guidance |
| Cordyceps, chaga, Trametes | No specific pre-operative data | None | Stop anyway, by general guidance |
| Culinary mushrooms as food | None identified | — | No — food is not the issue |
What About After Surgery?
The same logic applies in reverse and nobody discusses it. Restarting an antiplatelet-active extract while a wound is healing, or while on post-operative anticoagulation, reintroduces exactly the interaction you paused for.
There is no published guidance on when to restart mushroom supplements after an operation, because the question has never been studied. The defensible approach is to treat restarting as a decision to raise with the surgical team rather than a personal one, particularly if post-operative anticoagulants have been prescribed.
What to Actually Do
- Stop all mushroom supplements two weeks before elective surgery. That is the upper end of the ASA and AANA window and costs you nothing.
- Write them on the pre-assessment form by species and dose. "Herbal supplement" is not useful; "reishi extract, 1 g daily, 8 months" is.
- Say it out loud to the anaesthetist as well. Half to seventy per cent of patients never mention supplements, so the form alone is not enough.
- If you take warfarin or another anticoagulant, treat this as urgent. Maitake has a documented INR case, and the interaction question outranks any benefit — see our medication interactions guide.
- Do not rely on a normal clotting panel. Antiplatelet effects do not appear in prothrombin time, prothrombin ratio or INR.
- Ask before restarting. There is no evidence base for a restart interval, which makes it a conversation rather than a rule.
- Dental extractions and minor procedures count. Any procedure with a bleeding endpoint is the same question at smaller scale.
The Honest Summary
The evidence here is in vitro screening, mechanistic pharmacology and one case report — not clinical bleeding trials, and it would be wrong to describe it as more than that. What makes it worth acting on is the asymmetry. Stopping a mushroom supplement for two weeks costs nothing measurable; a platelet effect that standard pre-operative testing cannot see costs a great deal if it matters.
The species-specific concerns are reishi for platelets, maitake for INR on warfarin, and Amanita muscaria for its overlap with the receptor family anaesthesia works through. The general rule covers everything else: it is a supplement, the guidance says stop supplements, so stop — and say what you were taking.
Frequently Asked Questions
How long before surgery should I stop mushroom supplements?
Two weeks is the safe default. Professional anaesthesia guidance recommends discontinuing herbal medications one to two weeks before elective procedures, and there is no reason to take the shorter end of that window for a supplement you can simply pause.
Does reishi thin the blood?
In laboratory conditions it inhibits platelet aggregation, in one screen more strongly than 140 µmol/L aspirin on the ADP test. That is in vitro evidence rather than a clinical bleeding study, but it is enough to justify stopping before an operation.
Will my pre-operative blood test show that I take mushroom supplements?
No. Routine testing measures prothrombin time, prothrombin ratio and INR, and an in vitro screen of eight mushroom species found none of them altered any of those three. Antiplatelet effects are a different mechanism and are not routinely tested.
Do I need to stop eating mushrooms before surgery?
No. The concern applies to concentrated extracts taken daily at supplement doses, not to mushrooms as food in normal culinary quantities.
When can I restart mushroom supplements after an operation?
There is no published guidance, because the question has not been studied. Since post-operative anticoagulation is common and wound healing involves the same platelet systems, this is one to put to the surgical team rather than decide alone.
Shop Thoughtfully
If a procedure is on the calendar, the right move is to pause rather than to buy. When you do restart with clinical agreement, Reishi capsules (120 caps €39, 2 × 120 €70) make dosing easy to state precisely on a medication list, which matters more than it sounds. Lion's mane capsules (120 caps €49) showed no notable antiplatelet activity in the eight-species screen. Free shipping on orders over €50.
Related Articles
- Mushroom Supplements and Medication Interactions
- Maitake Side Effects and Interactions
- Reishi Side Effects and Drug Interactions
- Amanita muscaria Side Effects and Interactions
- Mushrooms and Blood Pressure Medication
- Cordyceps Side Effects and Interactions
- Mushroom Supplements During Pregnancy
Sources
- Poniedziałek B, Siwulski M, Wiater A, et al. The effect of mushroom extracts on human platelet and blood coagulation: in vitro screening of eight edible species. Nutrients. 2019;11(12):3040. PubMed 31842490
- Elvir Lazo OL, White PF, Lee C, et al. Use of herbal medication in the perioperative period: potential adverse drug interactions. J Clin Anesth. 2024;95:111473. PubMed 38613937
- Ang-Lee MK, Moss J, Yuan CS. Herbal medicines and perioperative care. JAMA. 2001;286(2):208-216. PubMed 11448284
- Hanselin MR, Vande Griend JP, Linnebur SA. INR elevation with maitake extract in combination with warfarin. Ann Pharmacother. 2010;44(1):223-224. PubMed 20040699
- Su CY, Shiao MS, Wang CT. Differential effects of ganodermic acid S on the thromboxane A2-signaling pathways in human platelets. Biochem Pharmacol. 1999;58(4):587-595. PubMed 10413295
- Su C, Shiao M, Wang C. Potentiation of ganodermic acid S on prostaglandin E1-induced cyclic AMP elevation in human platelets. Thromb Res. 2000;99(2):135-145. PubMed 10946087