The active chemical in "shrooms" is psilocybin. This is a hallucinogen obtained from certain types of mushrooms that are native to tropical and subtropical regions of South America, Mexico, and the United States. The use of psilocybin has also been associated with negative physical and psychological consequences. The physical effects, which appear within 20 minutes of ingestion and last approximately 6 hours, include nausea, vomiting, muscle weakness, drowsiness, and lack of coordination. The psychological side effects of psilocybin use include hallucinations and an inability to distinguish fantasy from reality. Panic attacks and psychosis may also occur, particularly if a person ingests a large dose. Also associated with the ingestion of psilocybin is the risk of poisoning if one of the many varieties of poisonous mushrooms is incorrectly identified as a psilocybin mushroom.
Please check out this webpage for additional information: https://www.drugabuse.gov/drugs-abuse/hallucinogens.