The injectable contraceptives depot medroxyprogesterone acetate and norethisterone enanthate substantially and...

HIV acquisition risk with norethisterone (NET) enanthate (NET-EN) is reportedly less than for depo-medroxyprogesterone acetate intramuscular (DMPA-IM). We investigated the effects of these progestin-only injectable contraceptives on serum testosterone and sex hormone binding globulin (SHBG) levels, since these may play a role in sexual behavior and HIV acquisition. The open-label WHICH clinical trial, conducted at two sites in South Africa from 2018-2019, randomized HIV-negative women aged 18-40 years to 150 mg DMPA-IM 12-weekly (n = 262) or 200 mg NET-EN 8-weekly (n = 259). We measured testosterone by UHPLC-MS/MS and SHBG by immunoassay in matched pairs of serum samples collected at baseline (D0) and at peak serum progestin levels at 25 weeks post initiation (25W) (n = 214-218 pairs). Both contraceptives substantially decreased, from D0 to 25W, the total testosterone [DMPA-IM D0 0.560, 25W 0.423 nmol/L, -24.3% (p < 0.0001); NET-EN D0 0.551, 25W 0.253 nmol/L, -54.1%, (p < 0.0001)], SHBG [DMPA-IM D0 45.0, 25W 32.7 nmol/L, -29.8% (p < 0.0001); NET-EN D0 50.2, 25W 17.6 nmol/L, -65.1% (p < 0.0001)], and calculated free testosterone levels [DMPA-IM D0 6.87, 25W 5.38 pmol/L, -17.2% (p = 0.0371); NET-EN D0 6.00, 25W 3.70, -40.0% (p < 0.0001)]. After adjusting for change from D0, the total testosterone, SHBG and calculated free testosterone levels were significantly higher for DMPA-IM than NET-EN (64.9%, p < 0.0001; 101.2%, p < 0.0001; and 38.0%, p = 0.0120, respectively). The substantial and differential decrease in testosterone and SHBG levels does not explain our previous finding of no detected decrease in risky sexual behavior or sexual function for DMPA-IM or NET-EN users from D0 to 25W. Medroxyprogesterone (MPA) and NET are androgenic and are both present in molar excess over testosterone and SHBG concentrations at 25W. Any within or between contraceptive group androgenic effects on behavior in the brain are likely dominated by the androgenic activities of MPA and NET and not by the decreased endogenous testosterone levels. The clinical trial was registered with the Pan African Clinical Trials Registry (PACTR 202009758229976).