Posthallucinogen-like visual illusions (palinopsia) with risperidone in a patient without previous hallucinogen exposure: Possible relation to serotonin 5HT2a receptor blockade

Background: Previous reports document visual illusions resembling hallucino gen persisting perception disorder (HPPD) after risperidone treatment in pa tients with histories of previous LSD exposure. Methods: We report a case w ith visual disturbances resembling HPPD after each of three consecutive ris peridone dose increases. Results: Contrasting with previous reports, our pa tient lacked any history of substance abuse, particularly hallucinogen expo sure. She lacked neurologic or other contributory illnesses. Illusions gene rally remitted within 48 hours each time. Coadministration of trazodone and clonazepam may have contributed to these phenomena, although clonazepam ha s been used to treat: this condition. She had been unusually sensitive to t he side-effects of many psychotropics. Conclusions: This case is unique due to the absence of substance abuse. This and another report note heightened sensitivity to medication side-effects. Visual phenomena resembling HPPD e vidently can occur with risperidone and, possibly, other atypical antipsych otics and certain antidepressants regardless of previous hallucinogen use. Several lines of evidence implicate reduced 5HT2a serotonin receptor stimul ation rather than increased 5HT2c stimulation.