Injectable contraceptives differentially affect the hypothalamic–pituitary-gonadal axis and amenorrhea incidence

Hormonal contraceptives modulate the hypothalamic-pituitary-ovarian (HPO) axis; however, underlying mechanisms and differences between contraceptives are underexplored. The Women's Health Injectable Contraception and HIV trial randomised 521 women to intramuscular depot medroxyprogesterone acetate (DMPA-IM) or norethisterone enanthate (NET-EN) and showed similar decreased estradiol levels, but more amenorrhea for DMPA-IM users. This secondary study excluded for misreporting contraceptive use for 128 participants (DMPA-IM n = 65; NET-EN n = 63). Peripheral blood serum collected at initiation and one week after the 24-week injection (25 W), at peak progestin levels, was analysed for gonadal steroids, progestins and peptide hormones. While no changes were detected in peripheral gonadotropin-releasing hormone levels, DMPA-IM decreased luteinising hormone (LH) less than NET-EN. DMPA-IM increased, while NET-EN decreased follicle-stimulating hormone (FSH). Both contraceptives substantially decreased gonadal steroid levels, more so in NET-EN users for testosterone and estradiol. Post-menopausal-like hypoestrogenic effects were greater than previously reported, consistent with the substantial reduction in LH levels. Whether reduced LH levels are due to direct pituitary, hypothalamic, or supra-hypothalamic effects by progestins, is unclear. MPA, unlike NET, increased fsh expression in LβT2 cells, likely via the glucocorticoid receptor, consistent with direct effects on the pituitary by MPA in women. Amenorrhea associated in a time-varying manner with MPA and HPO hormone levels and LH/FSH, for DMPA-IM but not NET-EN users. HPO hormone profiles differ between DMPA-IM and NET-EN users and compared to pre- and post-menopausal women. Mechanisms affecting amenorrhea likely differ between contraceptives, with lower 25 W LH/FSH being consistent with more amenorrhea for DMPA-IM.