A nonrandomized, open-label, multicenter study assessed the effects of body weight and injection site on the pharmacokinetics of medroxyprogesterone acetate (MPA) and its progestin medicating contraceptive efficacy among 77 healthy, fertile women aged 18-47 years. For determination of serum MPA concentration-time profiles, blood samples were collected before the 6th and 7th injections (day 0) and on days 3, 7, 14, 21, and 28 after the 6th and 7th monthly administrations. For injection site effects, MPA pharmacokinetics were compared at the injection sites of the arm, hip, and leg; there was no significant finding. For effects of body mass, no significant differences were noticed in the pharmacokinetics of MPA among the 3 body mass indices (thin/normal, obese, highly obese). However, a difference (p = 0.0387) was found between normal and obese women (20%). The findings suggest that minor differences observed in MPA pharmacokinetics have no impact on the contraceptive efficacy of MPA/E2C, may it be due to injection sites or body weight, since trough concentrations are well above the threshold levels required to suppress ovulation.