Microgestin 1/20
(brand name; formulation 1 mg of medroxyprogesterone acetate (MPA) in 20 mL of solution)
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What it is
- Active ingredient: Medroxyprogesterone acetate (MPA), a synthetic progestin.
- Form: Injectable solution (usually a single‑use vial).
- Dose: 1 mg MPA in 20 mL of aqueous vehicle (≈ 0.05 mg/mL).
- Delivery: Subcutaneous injection (most commonly into the abdomen or thigh).
- Regimen: One injection every 3 months (≈ 12 weeks) provides reliable contraception.
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How it works
- MPA is a progestin‑only contraceptive.
- It thickens cervical mucus, suppresses the mid‑cycle LH surge (preventing ovulation), and thins the endometrial lining, making implantation less likely.
- Because it contains no estrogen, it does not increase the risk of estrogen‑related side‑effects such as breast tenderness, headaches, or increased blood‑pressure in the same way that combined oral contraceptives do.
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Uses
- Primary: Long‑acting reversible contraception (LARC).
- Secondary (in some countries):
- Management of heavy or prolonged menstrual bleeding.
- Suppression of endometriosis‑related pain (off‑label).
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Typical dosing schedule
| Day | Administration | Location | Notes |
|-----|----------------|----------|-------|
| 0 | First injection | Abdomen or thigh | Should be administered by a trained professional. |
| 12 weeks | Re‑inject | Same site or alternate | Maintain 12‑week interval to keep contraceptive efficacy. |
If a dose is missed, the next injection should be given as soon as possible. Do not double‑dose to “catch up” – that can increase side‑effects without extra protection.
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Common side‑effects
| Category | Typical symptoms | Frequency |
|----------|------------------|-----------|
| Menstrual | Irregular bleeding, spotting, or amenorrhea (absence of periods) | Up to 70 % of users |
| Hormonal | Mood swings, decreased libido, breast tenderness | Variable |
| Metabolic | Weight gain, mild acne | Less common |
| Other | Headache, dizziness | Less common |
Note: Most side‑effects improve within the first 6–12 months. If bleeding becomes heavy or painful, contact your provider.
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Contraindications & Precautions
| Condition | Why it matters |
|-----------|----------------|
| Active liver disease | MPA is metabolized by the liver; liver dysfunction can increase drug levels. |
| Breast cancer or other estrogen‑sensitive cancers | Although progestin‑only, some risk is present with hormone therapy. |
| History of thromboembolism (deep‑vein thrombosis, pulmonary embolism) | Progestins can slightly raise clotting risk. |
| Pregnancy / suspected pregnancy | Should not be used. |
| Severe, uncontrolled hypertension | Hormonal changes can worsen blood pressure. |
| Untreated active infections in the injection site | Can lead to local inflammation or abscess. |
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Drug interactions
| Drug | Interaction | Clinical relevance |
|------|-------------|--------------------|
| Rifampicin / other strong enzyme inducers | Increases MPA clearance → reduced effectiveness. | May require additional contraception. |
| Cimetidine | Reduces MPA metabolism → higher hormone levels, risk of side‑effects. |
| Certain anticonvulsants (e.g., carbamazepine, phenobarbital) | Increase metabolism → lowered contraceptive efficacy. | Discuss alternative methods. |
| St. John’s wort | Increases hepatic enzymes → lowers MPA levels. |
| Hormonal birth control pills | No interaction, but concurrent use unnecessary. |
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Pregnancy & Lactation
- Pregnancy: Use only if absolutely needed; consult a clinician.
- Lactation: Safe; no significant drug excretion into breast milk. However, some mothers report changes in milk supply or infant fussiness; monitor and discuss with a pediatrician.
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Storage & Handling
- Store at 2–8 °C (refrigerator).
- Protect from light; keep vial sealed.
- Do not freeze.
- Once drawn or opened, discard after 24 h (use a fresh vial).
- Keep out of reach of children and pets.
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What to do if you miss a dose
- If within 2 weeks of the next scheduled dose:
- Get the injection as soon as possible.
- If you’re >2 weeks late:
- Use backup contraception (condoms) for at least 7 days after the missed dose.
- If you’re unsure:
- Call your pharmacist or provider for guidance.
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Frequently Asked Questions
| Question | Short answer |
|----------|--------------|
| Can I get an emergency “catch‑up” injection? | No – a missed dose should be administered as soon as possible, not doubled. |
| Will it affect my menstrual cycle? | Yes, many users experience irregular bleeding or amenorrhea; this usually stabilizes after a few months. |
| Is it safe for people with a history of depression? | Hormonal changes can influence mood; discuss your history with your provider. |
| Can I take other hormonal contraceptives at the same time? | Generally unnecessary; combining progestin‑only methods is not recommended unless advised by a clinician. |
| What if I experience severe headache or chest pain? | Seek medical attention immediately – these could be signs of thromboembolic events. |
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Bottom Line
Microgestin 1/20 is a reliable, long‑acting, progestin‑only contraceptive that requires a single injection every 3 months. It’s well tolerated by most people, but as with all hormone therapies, it carries a small risk of side‑