Objective: To investigate whether an early need of hormonal contraceptive (HC), or a failure to find a suitable method, are warning signs for endometriosis.

Design: A retrospective cohort study.

Setting: Sweden.

Population: The cohort consisted of 720 805 women aged 12-27 years during the period 2005-2017. All women, regardless of whether they received a diagnosis of endometriosis or not (reference group), were included.

Methods: We used data from Swedish national registers. Risks are expressed as crude and adjusted hazard ratios (HRs and aHRs, respectively) with 95% confidence intervals (95% CIs), adjusted for age, education level, civil status, parity, country of birth, and diagnoses of infertility, dysmenorrhea or depression.

Main outcome measures: A diagnosis of endometriosis between 12 and 27 years of age.

Results: During this period, 3268 women were diagnosed with endometriosis (0.45%). Women who started HC at the ages of 12-14 years had a higher risk of receiving the diagnosis (aHR 2.53, 95% CI 2.21-2.90) than those who began at age 17 years or older. Having tried more types of HCs was associated with a twofold increased risk of endometriosis (more that three types of HC, aHR 2.31, 95% CI 1.71-3.12). Using HC for more than 1 year was associated with a decreased risk of endometriosis (>1 year, aHR 0.53, 95% CI 0.48-0.59). Women with endometriosis more commonly had dysmenorrhea, depression or infertility.

Conclusions: The use of HCs at an early age and a failure to find a suitable HC were identified as warning signs of later receiving an endometriosis diagnosis. A longer duration of HC usage reduced the risk of receiving the diagnosis.