Hormonal Contraceptive Use Is Associated With a Decreased Incidence of Hypothyroidism

Objective: Hypothyroidism is one of the most common endocrine disorders affecting 5 to 10 times more women than men. Given this higher incidence in women, it is possible that hormonal differences or medications more commonly used by women may play a role in the risk of developing hypothyroidism. We hypothesized that hormonal contraception affects the risk of developing hypothyroidism. Methods: Using the TriNetX database, we developed a case-control study and identified women aged 18 to 45 years in 4 distinct groups: (1) estrogen-progestin contraceptive (EPC) use, (2) progestin-only contraceptive (POC) use, (3) progestin-containing intrauterine device (IUD) use, and (4) controls. For each group, we ascertained data including the diagnosis of hypothyroidism, alcohol use, tobacco use, and body mass index. Results: We identified 18 578 patients with sufficient data: EPC use, n = 5849; POC use, n = 5052; IUD use, n = 1000; and controls, n = 6677. A total of 118 individuals (1.8%) in the control group and 165 individuals (1.4%) who received hormonal contraception developed hypothyroidism. After using a logistic model to account for cofounding variables, all forms of hormonal contraception (EPC, POC, and IUD) had a protective effect against the diagnosis of hypothyroidism. POC and IUD uses had the greatest protective effect, with odds ratios of 0.14 and 0.12, respectively. EPC had a less pronounced but still significant effect, with an odds ratio of 0.30 (P < .001). Conclusion: This study of >18 000 women and the risk of developing hypothyroidism demonstrates a protective effect of hormonal contraceptive use. Our data, both unadjusted and adjusted using a logistic model to account for cofounding variables, suggest that the use of hormonal contraception, in any form, decreases the risk of developing hypothyroidism.