Lithium and GLP-1-based therapies in bipolar disorder: an emerging pharmacovigilance signal and monitoring considerations

Lithium remains a cornerstone of bipolar disorder treatment, yet it has a narrow-therapeutic index and depends on renal and volume status. Glucagon-like peptide-1 (GLP-1) receptor agonists and dual glucose-dependent insulinotropic polypeptide/GLP-1 agonists are now widely coprescribed in this population. Six bibliographically distinct reports published since 2025 describe lithium elevation or toxicity after initiation, switching, or escalation, and in June 2026 the European Medicines Agency’s Pharmacovigilance Risk Assessment Committee opened a signal of a drug interaction leading to increased lithium levels. We separate three levels of evidence: (a) an uncontrolled pharmacovigilance signal; (b) plausible mechanistic pathways; and (c) a speculative temporal model. The candidate mechanisms are more constrained than previously appreciated: delayed gastric emptying alters absorption rate without demonstrably altering total exposure; GLP-1-mediated natriuresis acts in the opposite direction and does not persist; reduced lithium clearance after weight loss is sustained but quantitatively insufficient. The temporal framing is speculative and may partly reflect ascertainment bias. The reports describe two separable phenomena: acute toxicity events, largely explicable by intake and volume effects, and a sustained upward shift in concentration per unit dose, which is not. We set out falsifiable predictions and monitoring considerations, adopting rather than claiming the schedule proposed elsewhere.