Abstract
BACKGROUND: Use of the high-dose levonorgestrel-releasing intrauterine system (LNG-IUS) has been associated with increased risk of incident depression. Evidence is lacking on the influence of use of two recently marketed low-dose LNG-IUS on risk of depression. This study aims to examine associations between use of different doses of LNG-IUS and risk of depression. METHODS: We conducted a nationwide prospective cohort study involving all first-time users of an LNG-IUS among all Danish nulliparous women aged 15-34 years with no medical history of depression, major psychiatric diseases, endometriosis, heavy menstrual bleeding, polyp, myoma, dysmenorrhoea, iron supplement use, abortion, and infertility treatment. FINDINGS: A total of 46,565 first-time users of LNG-IUS were followed for 80,516 person-years with 1,531 incident initiations of antidepressant use observed during follow-up. Use of the high-dose LNG-IUS containing 52 mg levonorgestrel was initiated by 9,902 (21%) women, while 20,665 (44%), and 15,998 (34%) initiated use of the low-dose LNG-IUS containing 19·5 mg and 13·5 mg levonorgestrel, respectively.The age-, calendar-time-, and education-standardised incidence rates of first-time depression per 1,000 person-years at full LNG-IUS duration were 30.8 (95% CI 23·6-39·5) for the 52 mg LNG-IUS, 19·8 (95% CI 16·1; 24·0) for the 19·5 mg LNG-IUS, and 17·7 (95% CI 14·4-21·5) for the 13·5 mg LNG-IUS-. Compared to the high-dose 52 mg LNG-IUS, the adjusted number of avoided depressions per 1,000 person-years were 11·0 (95% CI 7·1-14·9) for the 19·5 mg LNG-IUS and 13·1 (95% CI 9·6-16·6) for the 13·5 mg LNG-IUS. The corresponding adjusted rate ratios were 0·77 (95% CI 0·68; 0·88) and 0·85 (95% CI 0·75-0·96). The reduced risk of depression with low-dose LNG-IUS compared to high-dose LNG-IUS was observable throughout duration of use. INTERPRETATION: Use of low-dose LNG-IUS containing 19·5 mg and 13·5 mg levonorgestrel, respectively, were associated with a reduced risk of incident depression compared to use of the high-dose 52 mg LNG-IUS. The study suggests that low-dose LNG-IUS should be preferred over the high-dose LNG-IUS for contraceptive purpose. FUNDING: Sygeforsikringen "Danmark" grant: 2021-0128.