A hallucinogen is a psychoactive agent that may cause hallucinations and profound changes in perceptions, thoughts, emotions and/or consciousness. Some natural hallucinogens are found in plants and mushrooms, while others are man-made.

The broad term hallucinogen can be further divided into three basic subtypes: psychedelics, dissociatives and deliriants. Psychedelics are sometimes referred to as “typical” or “traditional” hallucinogens. Some of these include psilocybin (active ingredient in magic mushrooms), DMT, LSD and mescaline (active ingredient in the cactus peyote).

Traditional hallucinogens are thought to work by disrupting the interaction of nerve cells and serotonin, a neurotransmitter involved in the regulation of mood, hunger, muscle control, sensory perception and body temperature.

Dissociatives have historically been used as anesthetics and are known to produce feelings of sedation and detachment. They typically induce a dream-like state or trance. These include ketamine, PCP and nitrous oxide (laughing gas).

Deliriants, which include the anticholinergic drugs diphenhydramine (Benadryl) and dimenhydrinate (Dramamine) as well as uncured tobacco, are known for triggering a state of delirium, often accompanied by dysphoria and unpleasant hallucinations.

Throughout history, many cultures have used plant-based hallucinogens, such as magic mushrooms, ayahuasca or peyote, in their cultural ceremonies to promote healing and spiritual growth. Participants in these ceremonies report experiencing spiritual guidance, visions and/or feelings of detachment.

Currently, most hallucinogens are classified as either Schedule I or Schedule II controlled substances by the U.S. government. However, some hallucinogens have been making a comeback in scientific studies by demonstrating significant therapeutic potential.

For example, LSD-assisted psychotherapy has been found to effectively reduce anxiety in terminally-ill patients. Other studies have shown psilocybin to lessen feelings of depression, help people overcome alcohol and smoking addictions and help previously violent offenders stop aggressive behavior.

Example: Scientists are increasingly conducting studies to test the effects of hallucinogens on willing participants who struggle with mental illness or addiction.