Symptoms of mushroom poisoning may vary from gastric upset to organ failure resulting in death.

Serious symptoms do not always occur immediately after eating, often not until the toxin attacks the kidney or liver, sometimes days or weeks later.

Most "poisonous" mushrooms contain gastrointestinal irritants that cause vomiting and diarrhea (sometimes requiring hospitalization), but usually no long-term damage.

[17] This is a common occurrence with A. phalloides in particular, due to its resemblance to the Asian paddy-straw mushroom, Volvariella volvacea.

Foragers are encouraged to always cut the fruiting bodies of suspected puffballs in half, as this will reveal the outline of a developing Amanita should it be present within the structure.

Both are bright-orange and fruit at the same time of year, although Omphalotus grows on wood and has true gills rather than the veins of a Cantharellus.

[citation needed] Clitocybe dealbata, which is occasionally mistaken for an oyster mushroom or other edible species contains muscarine.

They contain a toxin called gyromitrin, which can cause neurotoxicity, gastrointestinal toxicity, and destruction of the blood cells.

[3] The Finns consume Gyromitra esculenta after parboiling, but this may not render the mushroom entirely safe, resulting in its being called the "fugu of the Finnish cuisine".

Thus, the symptoms of toxicity are similar to being hung over—flushing, headache, nausea, palpitations, and, in severe cases, trouble breathing.

However, after the death of the German mycologist Dr. Julius Schäffer, it was discovered that the mushroom contains a toxin that can stimulate the immune system to attack its red blood cells.

[24] Similarly, Tricholoma equestre was widely considered edible and good, until it was connected with rare cases of rhabdomyolysis.

[26] Some mushrooms might concentrate toxins from their growth substrate, such as Chicken of the Woods growing on yew trees.

[27] Of the most lethal mushrooms, five—the death cap (A. phalloides), the three destroying angels (A. virosa, A. bisporigera, and A. ocreata), and the fool's mushroom (A. verna)—belong to the genus Amanita, and two more—the deadly webcap (C. rubellus), and the fool's webcap (C. orellanus)—are from the genus Cortinarius.

[citation needed] The following species may cause great discomfort, sometimes requiring hospitalization, but are not considered deadly.

This can affect cells that replicate frequently, such as kidneys, livers, and eventually, the central nervous system.

Researchers have found that different mushroom species share the same type of amatoxin called amanitin.

The researchers also concluded that there is “an unknown ancestral fungal donor[32],” that allowed for horizontal gene transfer.

[34] However, it is believed that mammals pose a higher threat to mushrooms than fungivores, as larger body sizes mean they are more capable of eating an entire fungus in one sitting.

The second possible warning sign is olfactory aposematism, a similar concept, but instead of focusing on color, the odor of the mushroom would be what deters predation.

This proposes that the cap color does not act as a warning sign to deter predators, providing no evidence that poisonous mushrooms may not signal their toxicity through visual or chemical traits.

[33] The three deadly mushrooms listed above, Amanita, Galerina, and Lepiota, are all of different colors, consisting of reds, yellows, browns, and whites.

A possible theory as to why color is not a factor in determining whether a mushroom is poisonous is the fact that many of its predators are nocturnal and have poor vision.

However, certain types of mushrooms contain very potent toxins and are very poisonous; so even if symptoms are treated promptly, mortality is high.

[37] In 2012, 4 out of the 7 total deaths that occurred that year, were attributed to a single event where a "housekeeper at a Board and Care Home for elderly dementia patients collected and cooked wild (Amanita) mushrooms into a sauce that she consumed with six residents of the home.".

[38][39] Over 1,300 emergency room visits in the United States were attributed to poisonous mushroom ingestion in 2016, with about 9% of patients experiencing a serious adverse outcome.