This study examines a new medicine, ITI-1284, for those with Generalized Anxiety Disorder (GAD). GAD is when someone feels very anxious or worried most of the time. The study will compare ITI-1284 to a placebo (a fake treatment) to see if it helps people who haven’t been helped enough by their current medicine. The study has three parts: a Screening Period (up to 3 weeks) where doctors check if participants can join, a Treatment Period (6 weeks) where participants get either ITI-1284 or a placebo, and a Safety Follow-up (1 week) to check on participants' health.

• Participants need to be at least 18 years old and currently not responding well to certain GAD medicines.
• The study lasts a total of 10 weeks, including all periods.
• Participants will have a chance to receive a new treatment and will need to visit the study site several times.