Association Between Intrauterine System Hormone Dosage and Depression Risk

OBJECTIVE: The authors compared the associated risk of incident depression between first-time users of low-, medium-, and high-dose levonorgestrel-releasing intrauterine systems (LNG-IUSs). METHODS: This national cohort study was based on Danish register data on first-time users of LNG-IUSs, 15-44 years of age, between 2000 and 2022. Cox regression and a G-formula estimator were used to report 1-year average absolute risks, risk differences, and risk ratios of incident depression, defined as initiation of an antidepressant or receipt of a depression diagnosis, standardized for calendar year, age, education level, parental history of mental disorders, endometriosis, menorrhagia, polycystic ovary syndrome, dysmenorrhea, leiomyoma, and postpartum initiation. RESULTS: In total, 149,200 women started using an LNG-IUS, among whom 22,029 started a low-dose one (mean age, 22.9 years SD=4.5), 47,712 a medium-dose one (mean age, 25.2 years SD=6.2), and 79,459 a high-dose one (mean age, 30.2 years SD=5.6). The associated subsequent 1-year adjusted absolute risks of incident depression were 1.21% (95% CI=1.06-1.36), 1.46% (95% CI=1.33-1.59), and 1.84% (95% CI=1.72-1.96), respectively. For the users of high-dose LNG-IUSs, the risk ratios were 1.52 (95% CI=1.30-1.74) and 1.26 (95% CI=1.10-1.41) compared with users of the low- and medium-dose LNG-IUSs, respectively. For users of medium-dose LNG-IUSs, the risk ratio was 1.21 (95% CI=1.03-1.39) compared with users of low-dose LNG-IUSs. CONCLUSIONS: First-time use of an LNG-IUS was positively associated with incident depression in an LNG-dose-dependent manner across low-, medium-, and high-dose LNG-IUSs. Although the observational design of the study does not permit causal inference, the dose-response relationship contributes to the body of evidence suggesting a relationship between levonorgestrel exposure and risk of depression.