The investigators are doing this study to look at how different doses of the Depot medroxyprogesterone acetate (DMPA) shot effect weight gain and bone mineral density in teens. The investigators hope that what the investigators learn from this study will be used to develop ways to keep girls from gaining weight or losing bone density when receiving DMPA.

Depot medroxyprogesterone acetate (DMPA) is a generic form of the DepoProvera® shot. When receiving the birth control shot some girls gain a lot of weight while others do not. Some girls also lose bone mineral density (BMD). Bone mineral density is the amount of weight and thickness of the bones.

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.

Inclusion Criteria:

1. Age 12-21 years
2. Healthy, post-menarcheal female
3. Self-selected to initiate depot medroxyprogesterone acetate (DMPA)
4. Willingness to use a barrier method of contraception in addition to DMPA

Exclusion Criteria:

1. Chronic disease known to affect weight or bone mineral density (BMD) (e.g. diabetes, kidney)
2. Use of medication known to affect weight or BMD (e.g. corticosteroids)
3. DMPA use within the past 12 months
4. Pregnancy within the past 6 months
5. Etonogestrel implant, levonorgestrel-releasing intrauterine system or combined estrogen/progesterone contraceptive use within the past 30 days (OC, patch, vaginal ring)
6. Weight exceeding 450 lbs
7. Need for confidential contraceptive care for individuals < 18 years of age.

Up to 48 weeks

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