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Levonorgestrel

Hormonal Contraceptiveprescriptionoral · inferred

Second-generation 19-nortestosterone-derived progestin. The most widely used progestin globally: combined OCs (0.1-0.15 mg), progestin-only mini-pill, emergency contraception (Plan B, 1.5 mg single dose), and long-acting IUDs (Mirena, Skyla, Kyleena release 10-20 mcg/day locally). Strong progestogenic + moderate androgenic activity, no estrogenic or glucocorticoid activity. Primarily hepatic metabolism via CYP3A4 reduction, sulfation, and glucuronidation. Terminal half-life 24-32 h.

Projected serum levels — 150 mcg (≈ 0.15 mg), once daily

Levonorgestrel
Levonorgestrel modeled serum levels, 150 mcg (≈ 0.15 mg) once daily over 15 days Population-based pharmacokinetic estimate. Steady state reached after approximately 3 days. 0 0.25 0.50 0.75 1 Day 0 Day 4 Day 8 Day 11 Day 15 Time on a regular schedule ≈ steady state · day 3
Levonorgestrel modeled serum levels with a loading dose of 312 mcg, then 150 mcg (≈ 0.15 mg) once daily The first dose is larger so levels approach steady state faster. 0 0.25 0.50 0.75 1 Day 0 Day 4 Day 8 Day 11 Day 15 Time on a regular schedule

Maintenance schedule: 150 mcg (≈ 0.15 mg) once daily (oral).

Loading schedule: 312 mcg on day 1, then 150 mcg (≈ 0.15 mg) once daily — reaching therapeutic levels sooner.

Modeled steady state after ~3 days: peak ≈ 0.30 mg, trough ≈ 0.16 mg body load. Population-based estimate over 15 days for a reference dose at a 70 kg reference body mass — the interactive app scales curves to your doses, timing, and body mass.

Key facts

Category
Hormonal Contraceptive
Route modeled
Oral
Model confidence
inferred
Half-life
26 h
Common dose
150 mcg (≈ 0.15 mg)
Suggested maximum
1.5k mcg/day
Reference dose range
0.075–1.5k mcg (single dose)
Suggested cadence
once daily
Validated against
1.5 mg oral — Cmax 0.019 mg/L at 1.6 h

Documented interactions

  • contraindicated
    Efavirenz (Sustiva) + Levonorgestrel CYP induction

    Efavirenz (Sustiva) inducer of CYP3A4 predicted to change Levonorgestrel AUC by ~0.18x

  • contraindicated
    Rifampin + Levonorgestrel CYP induction

    Rifampin inducer of CYP3A4 predicted to change Levonorgestrel AUC by ~0.18x

  • danger
    7-Hydroxymitragynine (7-OH) + Levonorgestrel CYP inhibition

    Levonorgestrel reversible_inhibitor of CYP3A4 predicted to change 7-Hydroxymitragynine (7-OH) AUC by ~2.20x

  • danger
    Alfuzosin (Uroxatral) + Levonorgestrel CYP inhibition

    Levonorgestrel reversible_inhibitor of CYP3A4 predicted to change Alfuzosin (Uroxatral) AUC by ~3.33x

  • danger
    Alprazolam (Xanax) + Levonorgestrel CYP inhibition

    Levonorgestrel reversible_inhibitor of CYP3A4 predicted to change Alprazolam (Xanax) AUC by ~3.33x

  • danger
    Amlodipine (Norvasc) + Levonorgestrel CYP inhibition

    Levonorgestrel reversible_inhibitor of CYP3A4 predicted to change Amlodipine (Norvasc) AUC by ~3.33x

Serum checks 453 modeled interaction pairings for levonorgestrel across your whole stack — absorption conflicts, enzyme inhibition, and nutrient depletion included.

Research behind this entry

  1. Levonorgestrel: a review of its pharmacokinetics and pharmacology Fotherby K · Contraception, 1995 DOI

    Comprehensive PK review establishing LNG oral bioavailability ~95%, terminal t1/2 ~24-32h, 97% protein binding (SHBG + albumin).

  2. Emergency contraception with levonorgestrel: a pharmacokinetic and pharmacodynamic analysis Devoto L et al. · Contraception, 2002 DOI

    PK/PD study of 1.5 mg LNG emergency contraception demonstrating Cmax ~18 ng/mL at 2h and efficacy declining with time-since-intercourse.

  3. Effect of rifampin on the pharmacokinetics and pharmacodynamics of oral contraceptive containing ethinyl estradiol and norethindrone LeBel M et al. · Pharmacotherapy, 1998 DOI

    Established the magnitude of CYP3A4 inducer interactions with combined oral contraceptives, demonstrating ~30-50% AUC reductions.

3 published studies referenced in the app, each with a plain-language summary.