In this study 1 of 3 doses of DMPA will be given as an injection into the muscle in the arm. The 150mg dose is approved for use in this age group by the Food and Drug Administration (FDA) when given into the muscle. The 104mg dose is approved for use in this age group by the FDA only when given under the skin therefore it is considered experimental. The 75mg dose is also considered experimental as this dose is not FDA approved regardless of how it is given.