Hallucinogen use disorder is the DSM-5 category encompassing classical psychedelics (LSD, psilocybin, DMT, mescaline), dissociatives (ketamine, PCP, dextromethorphan at high doses), and entactogens (MDMA). Each subcategory has distinct pharmacology, risks, and emerging therapeutic applications.
Classical psychedelics (5-HT2A agonists): LSD, psilocybin, DMT, mescaline. Act primarily through 5-HT2A receptor agonism with downstream effects on multiple receptor systems. Low classical addiction potential — these substances do not produce the dopaminergic surge or compulsive use pattern of stimulants or opioids. No physical withdrawal syndrome.
Real but limited risks of classical psychedelics: acute "bad trips" with intense anxiety and impaired judgment that can produce dangerous behavior; rare emergence of persistent psychotic illness in genetically vulnerable individuals; rare hallucinogen persisting perception disorder (HPPD) with persistent visual disturbances (visual snow, palinopsia, after-images) lasting months to years after use; rare prolonged psychotic episodes in vulnerable individuals.
Dissociatives: ketamine, PCP, dextromethorphan at high doses act through NMDA antagonism with dissociative effects. Addiction potential is higher than classical psychedelics. Ketamine carries specific concerns about bladder toxicity (ulcerative cystitis) with chronic heavy use, and dependence patterns with regular use.
Entactogens: MDMA produces massive serotonin release through reversed SERT, plus dopamine and norepinephrine release. Acute risks: hyperthermia (particularly at high doses in poor environmental conditions), hyponatremia (from water intoxication during dancing), serotonin syndrome (especially combined with serotonergic medications). Persistent effects on serotonin signaling debated.
The therapeutic resurgence: after decades of regulatory restriction, psychedelic-assisted therapy has returned to research and is moving toward clinical practice. Psilocybin for depression and end-of-life distress (breakthrough therapy designation, late-stage trials). MDMA for PTSD (was on track for FDA approval pending recent FDA rejection of MAPS application in 2024 with calls for additional research). Ketamine and esketamine already FDA-approved for treatment-resistant depression — different therapeutic framework but related mechanism.
Therapeutic vs recreational distinction: the line between therapeutic and harmful use of these substances is contextual. Therapeutic use involves: structured setting, integration psychotherapy, careful patient selection (no psychotic vulnerability, no certain comorbidities), measured doses, no concurrent serotonergic medications, follow-up integration sessions. Recreational use lacks these protections.
When you encounter a patient with regular hallucinogen use, the assessment differs from other SUDs. Classical psychedelics rarely produce the compulsive use pattern that defines most SUDs. The patient's risks may be different — acute psychological harm, persistent perceptual changes, unmasking of primary psychotic illness, drug-drug interactions. Treatment is largely psychotherapeutic with attention to specific harms.