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.
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).