Controversies regarding lithium-associated weight gain: case–control study of real-world drug safety data

BACKGROUND: The impact of long-term lithium treatment on weight gain has been a controversial topic with conflicting evidence. We aim to assess reporting of weight gain associated with lithium and other mood stabilizers compared to lamotrigine which is considered free of metabolic adverse drug reactions (ADRs). METHODS: We conducted a case/non-case pharmacovigilance study using data from the AMSP project (German: “Arzneimittelsicherheit in der Psychiatrie”; i.e., Drug Safety in Psychiatry), which collects data on ADRs from patients treated in psychiatric hospitals in Germany, Austria, and Switzerland. We performed a disproportionality analysis of reports of weight gain (> 10% of baseline body weight) calculating reporting odds ratio (ROR). We compared aripiprazole, carbamazepine, lithium, olanzapine, quetiapine, risperidone, and valproate to lamotrigine. Additional analyses related to different mood stabilizers as reference medication were performed. We also assessed sex and age distributions of weight-gain reports. RESULTS: We identified a total of 527 cases of severe drug-induced weight gain representing 7.4% of all severe ADRs. The ROR for lithium was 2.1 (95%CI 0.9–5.1, p > 0.05), which did not reach statistical significance. Statistically significant disproportionate reporting of weight gain was reported for olanzapine (ROR: 11.5, 95%CI 4.7–28.3, p < 0.001), quetiapine (ROR: 3.4, 95%CI 1.3–8.4, p < 0.01), and valproate (ROR: 2.4, 95%CI 1.1–5.0, p = 0.03) compared to lamotrigine. Severe weight gain was more prevalent in non-elderly (< 65 years) than in elderly patients, with an ROR of 7.6 (p < 0.01) in those treated with lithium, and an ROR of 14.7 (p < 0.01) in those not treated with lithium. CONCLUSIONS: Our findings suggest that lithium is associated with more reports of severe weight gain than lamotrigine, although this difference did not reach statistical significance. However, lithium use led to fewer reports of severe weight gain than some alternative drugs for long-term medication (olanzapine, quetiapine, and valproate), which is consistent with recent studies. Monitoring of weight gain and metabolic parameters remains essential with lithium and its alternatives. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s40345-023-00313-8.