Adolescent women who use the injectable contraceptive depot medroxyprogesterone acetate lose bone mineral density each year they are on the drug but appear to rapidly recover that loss when the drug is withdrawn, results of a prospective study suggest.
When counseling young women on birth control methods, physicians should consider DMPA's effect on bone mineral density (BMD).
“The potential loss of bone density is one consideration of the many that go into a women's choice of contraceptive method,” said Delia Scholes, Ph.D., of the Center for Health Studies, Seattle, and her associates.
The researchers prospectively examined BMD in a cohort of 170 females aged 14-18. A total of 80 participants were using DMPA, and 90 were not. The DMPA-exposed teens were significantly more likely to be current smokers, to have been pregnant, have reached earlier menarche, and have a higher body mass index and body fat percentage (Arch. Pediatr. Adolesc. Med. 2005;159:139-44).
During the study, 61 of the DMP users discontinued the contraceptive, affording the opportunity to observe any subsequent changes in BMD.
The DMPA-exposed subjects were receiving the standard dose of 150 mg every 3 months. About 30% of them had received only 1 injection, 31% had received 2 or 3 injections, 21% had received 4-7 injections, and 18% had received at least 18 injections.
In the comparison group, 19% were using oral contraceptives at baseline.
BMD was measured at the hip, spine, and whole body every 6 months for 24-36 months.
After adjusting for baseline and time-dependent variables, the researchers determined that the DMPA users lost significantly more BMD at the hip (-1.81% vs. -0.19%) and spine (-0.97% vs. 1.32%), compared with nonusers. Both groups gained BMD when the whole body was measured, but the DMPA users gained significantly less than the nonusers (0.73% vs. 0.88%).
New users lost bone faster than continuous users. After 24 months, new users showed a -6.09% change at the hip, compared with -2.05% in continuous users and -0.92% in nonusers.
Among the 61 subjects who discontinued DMPA during the study, BMD increased. Their annualized adjusted mean change in BMD was 1.34% for hip, 2.86% for spine, and 3.56% for the whole body.
There was no significance in BMD between nonusers and those who had discontinued DMPA 18 months earlier.
The injection is highly effective in preventing pregnancy, and its quarterly administration helps reduce compliance problems sometime seen in young women using other contraceptives, the researchers said.
In 2004, the Food and Drug Administration issued a black box warning for DMPA stating that prolonged use of the drug could result in significant loss of bone density, that the loss is greater the longer the drug is administered, and that bone density loss may not be completely reversible after discontinuing the drug.