Many species of mushroom are poisonous. The potential for poisoning may vary within the same species, at different times of the growing season, and with cooking. It is difficult to differentiate poisonous from nonpoisonous mushrooms in the wild, even for highly knowledgeable people. Folklore rules are unreliable. (See also Overview of Poisoning.)
All poisonous mushrooms cause vomiting and abdominal pain. Other symptoms vary greatly depending on mushroom type. Generally, mushrooms that cause symptoms early (within 2 hours) of ingestion are less dangerous than those that cause symptoms later (usually after 6 hours).
Mushrooms that cause early gastrointestinal symptoms (such as Chlorophyllum molybdites and the little brown mushrooms that often grow on lawns) cause vomiting and diarrhea. These symptoms develop within 1-6 hours' time period. The diarrhea is occasionally bloody. Some people have headaches or body aches. Symptoms usually go away within 24 hours.
Mushrooms that cause early symptoms that affect the brain and spinal cord include hallucinogenic mushrooms, which contain the hallucinogen psilocybin. The most common are members of the Psilocybe genus, but some other mushrooms also contain psilocybin. They also cause nausea and vomiting within 15 to 45 minutes of ingestion. Symptoms begin within 20 to 90 minutes of ingestion and include euphoria, enhanced imagination, and hallucinations. A rapid heartbeat and high blood pressure often develop, and some children develop a fever. However, these symptoms go away without treatment, and serious consequences are rare, so specific treatment is usually not needed. However, if the person is very agitated, the doctor may give a sedative (such as lorazepam).
In poisoning caused by many species of Inocybe and some species of Clitocybe, the toxic substance is muscarine. Symptoms, which begin within 30 minutes after eating, may include
Although some of these symptoms are serious, in most people affected, symptoms are mild and usually go away within 12 hours. Doctors give atropine by vein (intravenously) to people who have severe symptoms, and nearly all people recover in 24 hours. Without treatment, death can occur in a few hours with severe poisoning.
Mushrooms that cause delayed gastrointestinal symptoms include Amanita phalloides and related types of mushroom (members of the Amanita, Gyromitra, and Cortinarius genera).
Amanita phalloides causes 95% of mushroom poisoning deaths. Vomiting and diarrhea start in 6 to 12 hours. Sometimes the blood sugar level drops dangerously low. Symptoms subside for a few days, but then people develop liver failure and sometimes kidney failure. Liver failure causes the skin to turn yellow (jaundice). People with kidney failure may have reduced urination or may have stopped urinating. Sometimes the symptoms disappear on their own, but about half of the people who have this type of poisoning die in 5 to 8 days. People with liver failure may survive if given a liver transplant.
Amanita smithiana mushrooms tend to cause delayed vomiting and diarrhea (about 6 to 12 hours after they are eaten). Kidney failure can occur within 3 days to 1 or 2 weeks after the mushrooms are eaten, and people often need temporary hemodialysis.
Gyromitra mushrooms also cause delayed vomiting and diarrhea and a low blood sugar level. Other problems include brain toxicity (such as seizures) and, after a few days, liver and kidney failure.
Most Cortinarius mushrooms originate in Europe. Vomiting and diarrhea may last for 3 days. Kidney failure, with symptoms of flank pain and a decreased amount of urine, may occur 3 to 20 days after the mushrooms are eaten. Kidney failure often resolves spontaneously.