Hypothesis: In a retrospective cohort of obese, GLP-1 receptor agonist (GLP-1 RA) initiators without recent major depressive disorder (MDD), we hypothesize that a rapid weight loss velocity (>1 kg/week) during the initial 90 days of treatment is associated with a higher hazard of incident MDD compared to gradual weight loss (<0.5 kg/week). We predict this association will be robust to extensive adjustment for confounding variables including baseline comorbidities, medications, and healthcare utilization patterns, and will be most pronounced in subgroups with pre-existing psychiatric vulnerability (e.g., anxiety disorders) and among female users.

Rationale: Current evidence on the psychiatric risks of GLP-1 RA is contradictory, likely due to significant indication and detection biases inherent in real-world data. Our hypothesis resolves this conflict by positing that the risk is not a direct pharmacological effect but is mediated by the physiological stress of rapid catabolism. This approach is supported by the need to meticulously control for a vast array of confounders identified in the literature—from metabolic and psychiatric comorbidities to medications—which existent studies may have inadequately addressed. By focusing on weight loss velocity, a currently uncharacterized patient response variable, we aim to isolate a specific, modifiable risk factor from the complex baseline characteristics of this population.

Proposed Experiment: Conduct a retrospective cohort study using electronic health records or claims databases (e.g., TriNetX, Optum, CPRD). Include adults with obesity (BMI ≥30) initiating GLP-1 RAs, excluding those with MDD diagnosis or antidepressant use in the 12 months prior. Classify patients into exposure groups based on weight loss velocity during the first 90 days: rapid (>1 kg/week), moderate (0.5-1 kg/week), and gradual (<0.5 kg/week). Primary outcome: incident MDD diagnosis or new antidepressant prescription within 12 months. Use Cox proportional hazards models with propensity score matching or inverse probability weighting to adjust for confounders including age, sex, baseline BMI, comorbidities (anxiety, PCOS, cardiovascular disease), concurrent medications, and healthcare visit frequency. Conduct subgroup analyses by sex and baseline psychiatric vulnerability (anxiety disorders, prior MDD >12 months ago).

References:

1. PMC.ncbi.nlm.nih.gov/articles/PMC11489
2. MDPI.com/2077-0383/11/11/176
3. DOM-Pubs.onlinelibrary.wiley.com/doi/10.1111/jdom.170175
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