Human dose-response data on GLP-1 psychiatric effects are absent from the literature despite mechanistic evidence that tonic receptor occupancy at therapeutic weight-loss doses suppresses dopamine signaling differently than lower psychiatric doses

This systematic review of 80 RCTs (107,860 participants) plus large cohort studies explicitly identifies the complete absence of human dose-response data on GLP-1 psychiatric effects as a critical evidence gap. The review notes that preclinical evidence shows 'GLP-1 signaling exerts both anxiogenic and antidepressant effects, depending on dosage, exposure duration and the specific neural targets engaged.' Despite years of clinical use at multiple doses (semaglutide 0.5mg, 1mg, 2mg; tirzepatide 2.5mg-15mg), no systematic dose-response study has been conducted. The review states: 'Most hypotheses about CNS involvement remain speculative due to lack of integrated neurobiological or mechanistic studies.' This gap is particularly significant given the mechanistic hypothesis that tonic receptor occupancy at high therapeutic doses (for weight loss) may suppress dopamine signaling differently than lower doses used in psychiatric contexts. The absence of this data means clinical practice is operating without understanding whether psychiatric effects are dose-dependent, reversible with dose reduction, or threshold phenomena.