Hallucinogens, also known as psychedelic drugs, are a class of substances known for their ability to alter perception, cognition, and emotions. Despite their profound effects on the mind, these drugs are non-addictive, setting them apart from many other abused substances. The mechanism of action of these drugs lies in their impact on the 5-HT_2A receptor in the brain. Upon activation, this receptor couples to G_q-type G proteins, triggering a cascade that releases intracellular calcium. This biochemical process is believed to underlie the unique psychological effects of hallucinogens. Psychedelic drugs can be divided into two main classes based on their chemical structure: indoleamines and phenethylamines. Indoleamine hallucinogens include LSD (lysergic acid diethylamide) and psilocybin, found in magic mushrooms. These drugs are known for producing vivid visual effects and a profoundly altered state of consciousness. However, they also have a downside - regular use can lead to rapid tolerance, requiring higher doses to achieve the same effects. While physical dependence is not typical, withdrawal symptoms can occur in some users. In severe cases, pharmacological intervention with drugs like diazepam may be necessary.

On the other hand, phenethylamines include substances like MDMA (3,4-Methylenedioxymethamphetamine), commonly known as ecstasy or molly, and PCP (Phencyclidine). MDMA is unique because it provides both stimulant and psychedelic effects, often eliciting feelings of empathy, euphoria, and heightened sensory perception. PCP, initially developed as an anesthetic, can cause emotional withdrawal and aggressive behavior at high doses. Like indoleamines, tolerance to phenethylamines can develop quickly, and medical intervention may be required in cases of overdose.