The risks associated with psychedelic drugs are mostly psychological, not physical. Physically, LSD is considered to be one of the least toxic drugs. Although lethal doses have been determined from experiments in several animal models, there has never been a recorded case of death exclusively attributed to LSD in humans.
Physical effects are minor but can vary 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 LSD are rare, and research suggests they may also be due to latent psychological disorders.
LSD 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 LSD. Though exact prevalence is unknown, HPPD is considered relatively rare, with no physical changes or neurological damage associated as the cause.