Some patients taking antiretroviral medications for HIV/AIDS receive the efavirenz, marketed under the commercial names Sustiva and Stocrin. According to a report in the LA Times by Melissa Healy, it has an "LSD-like interaction" with brain receptors governing serotonin activity.
That may explain why roughly half of patients taking efavirenz at the prescribed dose have reported neuropsychiatric side effects that include suicidal depression, night terrors, hallucinations, paranoia, psychosis and delusions. And it may also explain why efavirenz tablets are reportedly being ground up and smoked by drug abusers looking for a hallucinogenic high