What is the duration of effectiveness of the Depo (Depo-Provera, medroxyprogesterone acetate) shot as a contraceptive method for women of childbearing age?

Depo-Provera Duration of Effectiveness

The Depo-Provera shot provides contraceptive protection for 13 weeks (91 days), with injections scheduled every 3 months, though protection extends up to 15 weeks from the last injection. 1, 2

Standard Dosing Schedule

• Two formulations are available with equivalent effectiveness: 150 mg intramuscularly or 104 mg subcutaneously, both administered every 13 weeks 3, 1
• The FDA-approved dosing interval is every 3 months (13 weeks), with the intramuscular injection given as a deep injection in the gluteal or deltoid muscle 2, 4
• Many providers schedule appointments every 11-12 weeks to provide a buffer for missed appointments, ensuring continuous contraceptive coverage 1, 5

Grace Period for Late Injections

• If less than 2 weeks late (≤14 weeks from last injection): Proceed with the injection immediately—no backup contraception needed, as contraceptive protection remains intact 1
• If more than 2 weeks late (>14 weeks from last injection): The injection can still be given if reasonably certain the patient is not pregnant, but backup contraception (condoms or abstinence) must be used for 7 consecutive days after the injection 1
• There are no time limits on early injections; they can be given when necessary if a woman cannot return at the routine interval 1

Mechanism and Onset of Action

• After injection, medroxyprogesterone acetate (MPA) is detected in serum within 30 minutes 6
• Serum concentrations plateau at approximately 1.0 ng/mL for about 3 months, then gradually decline 6
• For initial injections: Backup contraception is required for the first 7 days after administration, as full contraceptive effect takes time to establish 1, 5
• The typical use failure rate is approximately 6% in the first year, though perfect use achieves a failure rate of only 0.2-0.3% 3, 2

Duration of Contraceptive Effect

• Contraceptive protection extends beyond the 13-week dosing interval due to the prolonged release of MPA from muscle tissue 6
• In some women, MPA can be detected in serum for as long as 9 months after a single 150 mg injection 6
• The 104 mg subcutaneous formulation suppresses ovulation for more than 13 weeks in all subjects, regardless of body mass index or race 7

Return to Fertility After Discontinuation

• Median time to conception is 10 months following the last injection, with a range of 4 to 31 months 2
• Based on life-table analysis, 68% of women who become pregnant may conceive within 12 months, 83% within 15 months, and 93% within 18 months from the last injection 2
• Median time for return to ovulation with the subcutaneous formulation is 30 weeks, with a 97.4% cumulative rate of return to ovulation at 12 months 7
• Ovulation resumes when MPA levels fall below 0.1 ng/mL 6

Critical Counseling Points

• Menstrual irregularities: Nearly all patients experience unpredictable spotting and bleeding initially, with amenorrhea becoming common (57% by end of first year) with continued use 1, 4
• Pre-injection counseling about menstrual changes significantly reduces discontinuation rates 1, 5
• Weight gain: Average weight gain is 5.4 lb after 1 year, 8.1 lb after 2 years, and 13.8 lb after 4 years; weight gain status at 6 months (>5% increase) predicts future excessive weight gain 1, 8, 2
• Bone mineral density: DMPA causes reversible reductions in BMD, but substantial recovery occurs after discontinuation 1, 8
• The American College of Obstetricians and Gynecologists does not recommend limiting use to 2 years despite the FDA black box warning, as pregnancy prevention benefits outweigh BMD risks 1, 5, 8

Bone Health Measures for All Users

• All patients must receive counseling on skeletal health promotion: daily intake of at least 1300 mg calcium and 600 IU vitamin D, regular weight-bearing exercise, and avoidance of smoking and alcohol 1, 5, 8

STI Protection Requirement

• Patients must be counseled to use condoms at all times for STI protection, as Depo-Provera provides no protection against sexually transmitted infections 1, 5, 2

Common Pitfall to Avoid

• Do not delay administering a late injection out of concern for pregnancy risk—it can be given at any time if reasonably certain the patient is not pregnant, though backup contraception will be needed for 7 days if more than 2 weeks late 1
• Do not fail to counsel about menstrual irregularities before the first injection, as this significantly reduces discontinuation rates 1, 5