The risks associated with psychedelic drugs are mostly psychological, not physical. Physically, psilocybin mushrooms are considered one of the least toxic drugs known. Although lethal doses have been determined from experiments in several animal models, recorded cases of death exclusively attributed to usual doses of psilocybin mushrooms in humans are extremely rare.
Physical effects are minor but varied and can be unique from person to person. The most consistent reactions, such as dilated pupils, elevated blood pressure, and increased heart rate, are usually mild, and considered side effects of emotional intensification.
However, these along with other reported symptoms like nausea, increased perspiration, numbing and tremors, can sometimes make psychological symptoms like anxiety, panic attacks, paranoia, and mood swings seem worse. Long-term physical effects directly attributed to the pharmacology of psilocybin are rare, and research suggests they may also be due to latent psychological disorders.
Psilocybin and "Flashbacks"
Hallucinogen Persisting Perception Disorder (HPPD), sometimes mistakenly referred to as “flashbacks,” is a condition unique to psychedelics, involving perceptual changes lasting weeks or months following the use of a drug like psilocybin. Though exact prevalence is unknown, HPPD is considered relatively rare, with no physical changes or neurological damage associated as the cause.