levonorgestrel
Brand: Plan B One-Step, Mirena IUD, Skyla IUD, Kyleena IUD
Prototype: medroxyprogesterone
Drug Class: progestogen
Drug Family: hormone
Subclass: 19-norprogesterone derived levonorgestrel
Organ Systems: endocrinereproductive
Mechanism of Action
Potent synthetic progestogen that prevents pregnancy via multiple mechanisms depending on dose and route: emergency contraceptive doses primarily delay or inhibit ovulation; lower IUD doses primarily thicken cervical mucus, thin endometrium, and alter tubal motility. Very low androgenic activity compared to older progestogens.
progesterone receptor
Indications
- emergency contraception (Plan B: within 72–120 hours)
- long-term contraception (Mirena IUD up to 7–8 years)
- heavy menstrual bleeding (Mirena)
- endometriosis (Mirena)
Contraindications
- known pregnancy
- uterine anomalies (for IUD)
- acute pelvic inflammatory disease (IUD)
- history of ectopic pregnancy (relative)
Adverse Effects
Common
- nausea
- irregular bleeding
- headache (emergency contraceptive)
- amenorrhea (IUD — desired)
- dysmenorrhea (IUD insertion)
Serious
- ectopic pregnancy (especially if contraceptive failure)
- IUD expulsion
- uterine perforation (IUD insertion)
- pelvic inflammatory disease (IUD)
Pharmacokinetics (ADME)
| Absorption | oral: rapid absorption; IUD: local release (~14–20 mcg/day Mirena) |
| Distribution | IUD: primarily local; oral: systemic distribution |
| Metabolism | hepatic |
| Excretion | renal and fecal |
| Half-life | ~36 hours (oral); sustained local release (IUD) |
| Onset | hours (oral EC); days (IUD) |
| Peak | 1–2 hours (oral) |
| Duration | single dose (EC); 7–8 years (Mirena IUD) |
| Protein Binding | 97.5% |
| Vd | moderate |
Drug Interactions
| Drug / Agent | Mechanism | Severity |
|---|---|---|
| CYP3A4 inducers (rifampin, phenytoin) | reduced levonorgestrel levels; reduced emergency contraceptive efficacy | major |
| ulipristal acetate | progestogen may reduce ulipristal efficacy if taken within 5 days of UPA | moderate |
Nursing Considerations
- Emergency contraception: administer as soon as possible after unprotected sex; effective up to 72 hours (some evidence for up to 120 hours); less effective in women >165 lbs.
- Counsel patients that emergency contraception does NOT cause abortion (works before implantation) and is not for regular use.
- For Mirena IUD insertion: ensure no pregnancy before insertion; educate about cramping during/after placement.
- Inform patients on enzyme-inducing medications that emergency contraceptive efficacy may be reduced; consider ulipristal acetate or copper IUD as alternative.
Clinical Pearls
- The levonorgestrel IUD (Mirena) is one of the most effective contraceptives available (failure rate <0.1%) AND treats heavy menstrual bleeding by reducing endometrial thickness, making it a preferred option for women with HMB who also need contraception.
- In overweight/obese women (>165 lbs), levonorgestrel emergency contraception has reduced efficacy; ulipristal acetate (ella) or copper IUD insertion are more reliable options.
Safety Profile
Pregnancy contraindicated
Lactation safe
Renal Adjustment Not required
Hepatic Adjustment Required
TDM Not required
Concordance Terms
Cross-referenced clinical concepts — click any term to see all content where it appears.