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Conjugated Estrogens (Premarin)

HRTprescriptionoral · inferred

Mixture of estrogens derived from pregnant mare urine (equilin, estrone, equilenin). NOT bioidentical. Brands: Premarin. Historically most prescribed HRT. Higher VTE and stroke risk than bioidentical estradiol. Half-life ~17h for dominant components.

Projected serum levels — 0.63 mg, once daily

Conjugated Estrogens (Premarin)
Conjugated Estrogens (Premarin) modeled serum levels, 0.63 mg once daily over 15 days Population-based pharmacokinetic estimate. Steady state reached after approximately 1 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 1

Maintenance schedule: 0.63 mg once daily (oral).

Modeled steady state after ~1 days: peak ≈ 0.14 mg, trough ≈ 0.024 mg body load. Population-based estimate over 15 days for a 0.63 mg dose at a 70 kg reference body mass — the interactive app scales curves to your doses, timing, and body mass.

Key facts

Category
HRT
Route modeled
Oral
Model confidence
inferred
Half-life
7 h
Common dose
0.63 mg
Suggested maximum
1.3 mg/day
Reference dose range
0.31–1.3 mg (single dose)
Suggested cadence
once daily

Documented interactions

  • danger
    Carbamazepine (Tegretol) + Conjugated Estrogens (Premarin) CYP induction

    Carbamazepine (Tegretol) inducer of CYP3A4 predicted to change Conjugated Estrogens (Premarin) AUC by ~0.36x

  • danger
    Efavirenz (Sustiva) + Conjugated Estrogens (Premarin) CYP induction

    Efavirenz (Sustiva) inducer of CYP3A4 predicted to change Conjugated Estrogens (Premarin) AUC by ~0.24x

  • danger
    Levothyroxine (Synthroid) + Conjugated Estrogens (Premarin) Protein binding

    Conjugated Estrogens (Premarin) may displace Levothyroxine (Synthroid) from plasma protein binding sites, transiently raising free drug concentration. This drug has a narrow therapeutic index; free…

  • danger
    Rifampin + Conjugated Estrogens (Premarin) CYP induction

    Rifampin inducer of CYP3A4 predicted to change Conjugated Estrogens (Premarin) AUC by ~0.24x

  • danger
    St. John's Wort (Hypericum perforatum) + Conjugated Estrogens (Premarin) CYP induction

    St. John's Wort (Hypericum perforatum) inducer of CYP3A4 predicted to change Conjugated Estrogens (Premarin) AUC by ~0.43x

  • danger
    Tacrolimus (Prograf) + Conjugated Estrogens (Premarin) Protein binding

    Conjugated Estrogens (Premarin) may displace Tacrolimus (Prograf) from plasma protein binding sites, transiently raising free drug concentration. This drug has a narrow therapeutic index; free…

Serum checks 250 modeled interaction pairings for conjugated estrogens (premarin) across your whole stack — absorption conflicts, enzyme inhibition, and nutrient depletion included.

Research behind this entry

  1. Risks and Benefits of Estrogen Plus Progestin in Healthy Postmenopausal Women (WHI) Rossouw JE et al. · JAMA, 2002 DOI

    Landmark WHI trial finding conjugated estrogen + MPA increased breast cancer, CVD, and stroke risk, reshaping HRT prescribing practices globally.

  2. Effects of Conjugated Equine Estrogen in Postmenopausal Women with Hysterectomy (WHI) Anderson GL et al. · JAMA, 2004 DOI

    WHI estrogen-alone arm showing conjugated estrogens without progestin had no increase in breast cancer risk but increased stroke risk.

  3. Menopausal Hormone Therapy and Long-Term All-Cause and Cause-Specific Mortality: The WHI Randomized Trials Manson JE et al. · JAMA, 2017 DOI

    18-year WHI follow-up showing no increased all-cause mortality from either HRT regimen, suggesting initial risks were time-limited.

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