After remission of a first-episode psychosis (FEP), antipsychotic discontinuation is associated with an increased risk of relapse compared to maintenance treatment. We studied short and longer-term effects of discontinuation of D2 receptor (D2R) antagonist and partial agonist antipsychotics on striatal dopamine D2/3R availability in FEP patients.

Remitted FEP patients underwent two [11C]raclopride PET scans to measure striatal D2/3R availability: 1 week after antipsychotic discontinuation (n = 16 antagonist users, n = 6 partial agonist users) and after being medication free for 6–8 weeks (n = 8 antagonist users, n = 5 partial agonist users). Fifteen matched healthy controls were scanned once. Psychotic relapse was monitored up to 12 months after discontinuation.

One week after discontinuation, D2R antagonist discontinuers showed higher striatal binding potential (BPND) than partial D2R agonist discontinuers (p < 0.001, CI = 0.749 to 1.681) and controls (p = 0.045, CI = 0.008 to 0.708), while partial agonist discontinuers had significantly lower BPND than controls (p = 0.001, CI = -1.326 to -0.386). 6-8 weeks after discontinuation, former antagonist users showed similar BPND to controls (p > 0.25), whereas former partial agonist users had higher BPND than controls (p = 0.027, CI = 0.069 to 1.085). Participants who discontinued antagonists relapsed more often (81%) than those who discontinued partial agonists (17%)(χ2 = 5.32, p = 0.021).

Discontinuation of partial D2R agonists may affect D2/3R availability differently than discontinuation of antagonists, which might explain the greater relapse risk after tapering antagonists than partial agonist antipsychotics.