Depot medroxyprogesterone acetate, an injectable contraceptive that is commonly used worldwide, has an impressive safety and efficacy record. However, recent studies have suggested that prolonged use may be associated with bone density loss, thus predisposing women who use this contraceptive to osteoporosis. Scholes and colleagues sought to verify the effect of depot medroxyprogesterone acetate on bone density in a population-based cross-sectional comparison of American women.

Women aged 18 to 39 years who were enrolled in a large group health plan participated in the study. A total of 183 women who were receiving depot medroxyprogesterone acetate injections were matched by age to control subjects attending the same clinic. Women who were pregnant, intending pregnancy or had any condition that could adversely influence bone density were excluded from the study.

At entry to the study, patients were measured and weighed, and completed extensive surveys that assessed demographic characteristics and factors affecting bone density. Bone densities were measured at proximal femur, lumbar spine and whole body.

The women using the injectable contraceptive were more likely than control subjects to be smokers, to be nonwhite, to be physically active and to be parous. They were also less likely to have completed high school, or report a previous fracture. Users reported first pregnancy at a younger age than control subjects.

The age-adjusted mean bone density levels for lumbar spine were significantly lower among users than among control subjects and lower at all other anatomical sites. After adjustment for other risk factors for reduced bone density, the differences were significant at the femoral neck, spine and trochanter. A significant dose-related response was found with the loss of bone density related to duration of medroxyprogesterone use. The most pronounced differences between users and control subjects were found in the youngest women (18 to 21 years).

The authors discuss the serious implications of their findings for the development of osteoporosis in users of this form of contraception. Inhibition of development of bone density in young women may lead to severe bone pathology at a younger age than in non-users. They are particularly concerned about the use of depot medroxyprogesterone in teenagers with other risk factors for low bone density.