Overview
Medroxyprogesterone acetate is a long-acting progestin contraceptive injection administered intramuscularly every 3 months. It works primarily by inhibiting ovulation and thickening cervical mucus to prevent pregnancy. This injectable formulation provides reversible contraception with high efficacy when administered on schedule.
Mechanism of Action
Medroxyprogesterone acetate is a synthetic progestin that exerts its contraceptive effects through multiple mechanisms: suppression of gonadotropin secretion (primarily LH surge) to inhibit ovulation, thickening of cervical mucus to impede sperm penetration, and endometrial thinning to prevent implantation.
Indications
- Contraception in females of reproductive potential
- Endometriosis-associated pain (off-label)
- Abnormal uterine bleeding management (off-label)
- Endometrial hyperplasia prevention (off-label)
Common Doses
- 150 mg/1 mL
- 150 mg per injection
Dosage
150 mg administered by deep intramuscular injection every 13 weeks (3 months). First dose should be given during the first 5 days of a normal menstrual period or within 5 days postpartum if not breastfeeding. Subsequent doses must be administered every 11-13 weeks for continuous contraceptive protection.
Black Box Warning
Black Box Warning: Prolonged use may result in significant bone mineral density loss, which may not be completely reversible
Contraindications
- Active thrombophlebitis
- Current or history of thromboembolic disorders
- Cerebral vascular disease
- Known or suspected breast cancer
- Hypersensitivity to medroxyprogesterone acetate or any formulation components
- Significant liver disease
- Undiagnosed abnormal vaginal bleeding
- Known or suspected pregnancy
Side Effects
- Menstrual irregularities (amenorrhea, spotting, breakthrough bleeding)
- Weight gain
- Headache
- Abdominal pain/discomfort
- Dizziness
- Fatigue
- Decreased libido
- Mood changes/depression
- Bone mineral density loss with long-term use
- Thromboembolic events
- Allergic reactions
- Breast tenderness
- Nausea
- Hair loss
Interactions
- Aminoglutethimide may decrease contraceptive efficacy
- Anticonvulsants (carbamazepine, phenytoin, phenobarbital) may reduce contraceptive effectiveness
- Antibiotics (rifampin, rifabutin) may decrease contraceptive efficacy
- St. John's Wort may reduce contraceptive effectiveness
- Warfarin monitoring may be required due to potential interaction
Counseling Points
- Must be administered every 3 months (13 weeks) for continuous contraceptive protection
- Irregular bleeding is common, especially during first year of use
- Long-term use may cause bone density loss - discuss calcium/vitamin D supplementation
- Does not protect against sexually transmitted infections
- Return of fertility may be delayed after discontinuation
- Report severe headaches, chest pain, shortness of breath, or leg pain immediately
- Regular breast self-exams and clinical breast exams recommended