The 70% jump in Acadia Pharmaceutical’s shares this morning shows that few were expecting a positive readout from the Harmony study, testing Nuplazid in dementia-related psychosis. Only the top-line hit was announced: the trial was stopped early for efficacy after the drug demonstrated a “highly statistically significant” longer time to relapse of psychosis, compared with placebo. The magnitude of effect remains the big unknown here, and Acadia executives were tight-lipped on a call this morning, pending presentation of full data at a medical conference. Safety will also be important when these data emerge, as concerns have been raised in the past; all the company said today was that nothing surprising had been detected in Harmony. Acadia intends to approach the FDA next year about label expansion, and it remains to be seen whether approval will be possible on the back of a single study. Dementia-related psychosis represents a much bigger market – ten times bigger, according to the company – than Parkinson’s disease psychosis, in which Nuplazid is already approved, so the regulator is sure to proceed cautiously here. Nuplazid is forecast, according to EvaluatePharma consensus, to make $1.1bn in Parkinson’s psychosis alone in 2024. Investors seem convinced of the opportunity for now, with Acadia’s market cap ballooning by $2.2bn in early trade.