AC-90179 is a piperidine derivative which acts as an inverse agonist at the 5-HT<sub>2A</sub> serotonin receptor and an antagonist at 5-HT<sub>2C</sub>. It was developed as a potential antipsychotic but was not pursued for medical applications due to poor oral bioavailability; however, it continues to be used as a tool compound in pharmacological research.