HTR1A and Parkinson disease: The key findings of this phase 2A, randomized, double‐blind, placebo‐controlled study are that NLX‐112, a first‐in‐class, highly selective 5‐HT1A receptor full agonist (1) was safe and generally well‐tolerated in PwP with troublesome LID; (2) reduced LID from baseline values, as assessed by the UDysRS; (3) reduced PD symptoms from baseline values, as assessed by UPDRS, including reduction of motor disability (UPDRS Part 3); and (4) numerically improved CGI‐C scores more than placebo‐treated PwP.