Primary aldosteronism (PA) and oral contraception (OC) can both cause hypertension in young women. However, the effect of OC on the screening test for PA, the aldosterone to renin ratio (ARR), is not clear.We evaluated the impact of OC on the screening test for PA.In this retrospective cohort study, we analyzed data from the female offspring (Gen2) of women enrolled in the Raine Study, a population-based birth cohort, who had blood pressure (BP) measurements, blood samples, and information about OC use at age 17 years (N = 484) and/or age 27 years (N = 486).Aldosterone concentration was significantly higher in OC users than nonusers at 17 years (median 486 pmol/L vs 347 pmol/L, P < 0.001). Renin concentration was significantly lower in OC users at both 17 years (13.4 mU/L vs 20.6 mU/L) and 27 years (9.2 mU/L vs 11.8 mU/L), hence the ARR was significantly higher in OC users compared to nonusers at both 17 years (31.5 vs 18.3) and 27 years (27.3 vs 21.1). The proportion of participants with ARR > 70 pmol/mU (current threshold for PA detection) was significantly higher in OC users at both 17 years (12.6% vs 2.1%) and 27 years (6.4% vs 0.4%); however, they had comparable BP to those with ARR < 70. OC use at any age abolished the relationship between ARR and BP that is observed in nonusers.OC can increase the ARR and cause a false positive PA screening result. Until more reliable criteria for PA screening in OC users are established, alternative contraception should be considered during screening.