TAK-503

TAK-503 (also known as S-42648) is a small molecule dopamine D1 receptor positive allosteric modulator (PAM) that was developed by Takeda, in collaboration with Shionogi, for the treatment of attention-deficit/hyperactivity disorder (ADHD). Unlike traditional stimulants that act as dopamine reuptake inhibitors or releasing agents, TAK-503 selectively enhances signaling at the D1 receptor by modulating its response to endogenous dopamine. This mechanism is intended to improve cognitive function and reduce ADHD symptoms with a potentially lower risk of side effects or abuse compared to conventional stimulants. Clinical development reached Phase 2 in adults and Phase 1 in children and adolescents; however, Takeda terminated the program in 2020 due to strategic business decisions.