Psychedelics, as explained by Matthew Johnson, are substances that have the ability to profoundly alter one's sense of reality. This can include a significant change in the sense of self. The term "psychedelic" spans several pharmacological classes and is often used synonymously with "hallucinogen". Classic psychedelics include substances like LSD, psilocybin (found in magic mushrooms), DMT (found in many plants), and mescaline (found in peyote cacti and other cacti like San Pedro). These substances can reveal aspects of the mind that are typically not accessible, including repressed memories and other unconscious material.