Pimavanserin and Aggression and Social Cognition.

The investigators are studying how certain drugs can reduce anger outbursts in people with anger problems. In this study the investigators seek to determine if a single 34 mg (two 17 mg tablets) oral dose of the 5-HT2a receptor blocker, pimavanserin, will reduce aggressive responding in individuals with impulsive aggression (Intermittent Explosive Disorder: IED) on a laboratory task that assesses aggression (Taylor Aggression Paradigm: TAP). We will also be examining how this drug impacts hostile social cognition e.g., hostile attribution). If pimvanserin reduces aggression in this study a next step would be a placebo-controlled treatment trial of pimavanserin in study participants with IED. Participation will first involve a remote (e.g., TEAMS) screening session. If potential study participants appear eligible they will come into the lab for an in-person session where participants will complete interviews and questionnaires and have a medical evaluation (including a physical exam, electrocardiogram, and screens for alcohol and drug use). During the next study session, participants will complete a diagnostic interview and a series of questionnaires, all of which can all take place on-line. During the next two sessions (which will be in-person) participants will undergo two (2) study sessions during which study participants will be given a study drug (orally). The drug given, pimavanserin, is currently available and is known to block serotonin receptors thought to be involved in regulating anger. After participants take the study drug, study participants will complete questionnaires and computer tasks for assessment of aggression and of hostile social cognition. Each of these two in-person study sessions will take at least eight (8) hours. A final on-line session will be done to make certain the investigators have all the data required by the study protocol.