For millions of women using hormonal contraception, a fundamental safety assumption may need revisiting. Meningiomas — typically slow-growing tumors arising from the brain's protective membranes — have long been associated with high-dose therapeutic progestogens, but whether the lower doses found in contraceptives carry meaningful risk has remained poorly defined. This large Danish study offers the most rigorous population-level evidence yet on that question.
Drawing on 25 years of nationwide registry data spanning January 2000 through December 2024, this nested case-control study enrolled approximately 3 million females aged 15 to 59 with Danish residence. Meningioma cases were identified through the Danish National Cancer Register and matched at a 1:10 ratio to controls on age, birthplace, and marital status. Progestogen exposures were granularly categorized by both active compound and route of administration — distinguishing, for example, levonorgestrel-releasing intrauterine systems from oral progestin-only pills — and assigned based on the most recent use prior to diagnosis. This design allows differentiation of risk by specific molecule, a critical methodological advance over prior aggregate analyses.
The findings matter clinically because contraceptive progestogens are structurally and pharmacologically diverse, and lumping them together obscures which formulations, if any, drive risk. Progesterone receptor affinity varies considerably across synthetic progestins, which likely determines tumor-promoting potential. The high-dose progestogens most firmly implicated in meningioma — cyproterone acetate, nomegestrol acetate, and chlormadinone — are rarely used as primary contraceptives, making extrapolation from those data to pill or IUD users scientifically questionable. This study's 25-year window and cohort scale give it substantial statistical power to detect even modest risk elevations in contraceptive-dose ranges. Key limitations include the observational, non-causal design and potential detection bias, since hormonally-treated women may receive more neuroimaging. Overall, this represents an important, potentially practice-shaping contribution to reproductive pharmacovigilance.