⚠️ Muscarine — The Cholinergic Mushroom Toxin Explained

Summary: Muscarine is a naturally occurring alkaloid in certain mushrooms that activates muscarinic acetylcholine receptors in the human body. It causes a characteristic cholinergic syndrome (salivation, sweating, tearing, diarrhea, miosis, etc.). This article covers its chemistry, occurrence, mechanism of action, symptoms, toxicity, diagnosis, treatment, prevention, and practical advice for mushroom foragers.

1. Introduction

Discovered in the 19th century, muscarine gave its name to the muscarinic class of acetylcholine receptors. It is most clinically significant in mushrooms of the genera Inocybe (fibrecaps) and Clitocybe (funnel mushrooms), although traces have been found in some Entoloma and Mycena species. Contrary to early assumptions, Fly Agaric (Amanita muscaria) contains only negligible muscarine; its main psychoactive compounds are muscimol and ibotenic acid.

2. Chemistry & Properties

• Muscarine is a quaternary ammonium alkaloid (L‑(+)-muscarine).

• Highly water‑soluble and polar → poor penetration of the blood‑brain barrier; effects are mostly peripheral.

• Heat‑stable and not destroyed by normal cooking — culinary preparation is not a safeguard.

3. Which Mushrooms Contain Muscarine?

The most important muscarine‑containing mushrooms are:

• Deadly Fibrecap — Inocybe erubescens (also known as Inosperma erubescens)

• Other Inocybe species (fibrecaps) — numerous small brown mushrooms, many muscarine‑positive.

• Fool’s Funnel / Ivory Funnel — Clitocybe dealbata

• Sweating Mushroom — Clitocybe rivulosa

• Occasionally: some Entoloma and Mycena species.

⚠️ Small, nondescript white or brown funnels and fibrecaps on lawns or in forests should never be consumed.

4. Mechanism of Action

• Muscarine is an agonist at muscarinic acetylcholine receptors (M1–M5).

• Overstimulation leads to excessive parasympathetic activity:

  • M3: secretion (saliva, tears, sweat), intestinal hypermotility, bronchoconstriction.

  • M2: bradycardia and impaired AV conduction.

• Because it barely crosses the blood‑brain barrier, central effects are limited; toxicity is mainly peripheral.

5. Clinical Symptoms

Onset: 15–60 minutes after ingestion.

Typical cholinergic (SLUDGE) syndrome:

• Salivation (excessive drooling)

• Lacrimation (tearing)

• Urination (frequent urination)

• Defecation / diarrhea

• Gastrointestinal upset

• Emesis (vomiting)

Additional signs:

• Sweating

• Miosis (constricted pupils), blurred vision

• Bradycardia, hypotension

• Bronchospasm, shortness of breath

• Severe cases: arrhythmias, respiratory distress, circulatory collapse

Duration: usually several hours, occasionally up to 24 h.

6. Toxicity & Lethality

• Muscarine poisoning is rarely fatal compared to amatoxins or gyromitrin.

• Most deaths occur in children, the elderly, or with delayed treatment.

• Main risks: severe bronchoconstriction, bradycardia, or circulatory failure.

7. Diagnosis

• History: rapid onset of cholinergic symptoms after mushroom ingestion.

• Physical exam: SLUDGE signs, miosis, bradycardia, bronchospasm.

• Laboratory tests: electrolyte imbalance, ECG monitoring. Specific toxin assays are rarely necessary for acute management.

8. Treatment & Management

Muscarine poisoning is a medical emergency.

Immediate Measures

• Hospitalization and monitoring of vital signs.

• Activated charcoal or gastric lavage if early after ingestion (under medical supervision).

Specific Antidote

• Atropine is the treatment of choice. It competitively blocks muscarinic receptors, reversing symptoms.

• Repeated doses or continuous infusion may be required depending on severity.

Supportive Care

• Oxygen, bronchodilators for bronchospasm.

• IV fluids for hypotension.

• ECG monitoring for arrhythmias.

9. Prevention & Foraging Advice

• Never consume small white or brown funnels or fibrecaps.

• Protect children and pets — lawns often host muscarine‑containing species.

• Preserve mushroom remnants or photos for identification in case of suspected poisoning.

10. FAQ

Does Fly Agaric contain muscarine?Only in negligible amounts. Its psychoactive effects are due to muscimol and ibotenic acid.

Can cooking destroy muscarine?No. It is heat‑stable and remains toxic.

How long do symptoms last?Usually several hours; with atropine treatment, recovery is rapid.

11. Conclusion

Muscarine is a well‑studied cholinergic toxin present in fibrecaps and funnel mushrooms. Although rarely fatal when treated, it can be dangerous without prompt care. With a clear antidote (atropine), outcomes are generally good — but prevention remains key: never eat unidentified small mushrooms.

Disclaimer: This article is for informational purposes only and not a substitute for medical advice. In suspected mushroom poisoning, seek emergency medical care immediately.