Gyromitra Mushroom Toxicity

Updated: Apr 28, 2023
  • Author: Reed Brozen, MD; Chief Editor: Sage W Wiener, MD  more...
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Practice Essentials

Thousands of mushroom species are studied and collected by amateur mushroom hunters, but only a handful cause death. False morel mushrooms (eg, Gyromitra esculentaGyromitra ambiguaGyromitra infula) can cause fatal poisonings. [1] These mushrooms are found on the ground or on rotten wood, are orange-brown to brown, have no gills, and have convoluted brainlike caps that are occasionally saddle-shaped. Gyromitra species fruit in the spring, and most poisonings occur during spring or early summer.



Some Gyromitra mushrooms contain hydrazones, including the toxin gyromitrin (N -methyl-N-formylhydrazone). Gyromitrin rapidly decomposes in the stomach to form acetaldehyde and N-methyl-N-formylhydrazine, which is converted to monomethylhydrazine (MMH) by slow hydrolysis. MMH is a water-soluble toxin that causes gastroenteritis, hemolysis, methemoglobinemia, hepatorenal failure, seizures, and coma. MMH is employed in rocket fuel and causes similar toxicity in aerospace industry workers. Cooking can render these mushrooms less toxic, although not reliably so. MMH is volatile and the fumes from cooking may cause toxicity.


MMH exposure is similar to that of isoniazid in that it generates functional pyridoxine deficiency by inhibition of pyridoxine kinase. Pyridoxine kinase inhibition interferes with production of pyridoxal phosphate, an essential cofactor for a number of enzymatic steps, including glutamic acid decarboxylase (GAD).

Gamma-aminobutyric acid (GABA), the primary inhibitory neurotransmitter of the brain, is produced from glutamate (an excitatory neurotransmitter) by the enzyme GAD. MMH also may inhibit GAD directly. The resultant GABA deficiency, with loss of inhibitory neurotransmission, may lead to seizures.

Gastrointestinal toxicity

Inhibition of diamine oxidase in intestinal mucosa may be responsible for GI effects. Association of individual variability in acetylation rates (eg, slow vs fast acetylators) in hepatotoxicity is not well established. [2]

Hematopoietic toxicity

Hemolysis and methemoglobinemia can occur. Resultant hemoglobinuria may cause acute kidney injury.



MMH poisoning may occur after ingestion of fresh, dried, or raw gyromitrin-containing mushrooms or with inhalation of vapors while cooking gyromitrin-containing mushrooms. 

Severity depends on amount of toxin ingested. Amount of toxin greatly varies among mushrooms, and significant variation in individual susceptibility exists. Raw mushrooms have more toxin than cooked mushrooms. Fresh mushrooms have more toxin than dry mushrooms. Environmental factors appear to influence the amount of toxin, which varies regionally in these mushrooms.



In 2021, the American Association of Poison Control Centers (AAPCC) Toxic Exposure Surveillance System reported 6783 single exposures to mushroom and 3 fatalities. [3]  Unknown mushroom type makes up the majority of exposures each year, usually accounting for well over 70% of mushroom exposures, but deaths in this group remain remarkably low (0-3 per year since 1996). [3, 4, 5, 6, 7, 8, 9, 10]

In the same 2021 report, MMH-containing mushrooms accounted for 32 exposures and no fatalities. [3]

No adequate international database exists. In the past, gyromitrin-containing mushrooms have been associated with significant mortality in Eastern Europe.

Mushroom poisoning is the leading cause of foodborne disease outbreaks and foodborne-related deaths in China. The Chinese Foodborne Disease Outbreak Surveillance System reported a total of 10,036 mushroom poisoning outbreaks between 2010-2020 with over 60% of the outbreaks attributed to unidentified mushrooms. These outbreaks resulted in a cumulative 38,676 illnesses and 788 deaths during that period.  In 2020 there were 2075 mushroom outbreaks reported. [11]  Gyromitra venenata was a new species discovered in two provinces in 2020 and caused poisoning in four patients. Poisonings due to gyromitrins had not been reported in China since 2000. [12]

Children are more sensitive to gyromitrin toxicity than adults. Overall about 60% of mushroom exposures are in children younger than 6 years. Although with Gyromitra species specifically, in 2017 children younger than 6 years account for less than 1% of exposures. [3]



Most patients fully recover after 2-5 days of a gastric illness. Mortality rates from 10-40% have been reported; however, death from gyromitrin-containing mushrooms in North America is exceedingly rare. Toxicity of gyromitrin-containing mushrooms varies by region and season.

Complications of MMH poisoning include:

  • Aspiration pneumonia
  • Rhabdomyolysis
  • Acute kidney injury secondary to hemolysis and rhabdomyolysis
  • Liver failure
  • Anoxic and hepatic encephalopathy

Patient Education

Inform patients that Gyromitra mushrooms are toxic and potentially lethal.

For patient education information, see visit eMedicineHealth's First Aid and Injuries Center. Also, see eMedicineHealth's patient education articles Poisoning and Activated Charcoal.