Short answer: Conjugated estrogens has a half-life of about 26.7 hours (total estrone, 0.625 mg; 14.8 hours baseline-adjusted). Levels peak about 6.9 hours (total estrone, 0.625 mg) after a dose. People vary, so treat these as estimates.
Conjugated estrogens are a mix of estrogens, mainly estrone and equilin, taken by mouth for menopause symptoms. They are sold as Premarin tablets (Pfizer), and combined with the progestin medroxyprogesterone acetate as Prempro (one daily tablet) and Premphase (a 28-day two-tablet sequence) for women with a uterus.
Also known as: Premarin, Prempro (with medroxyprogesterone), Premphase, CE.
Premarin comes as 0.3, 0.45, 0.625, 0.9 and 1.25 mg tablets. Prempro comes in four strengths from 0.3 mg/1.5 mg to 0.625 mg/5 mg (conjugated estrogens/medroxyprogesterone). Premphase is a 28-tablet pack: 0.625 mg conjugated estrogens on days 1 to 14, then 0.625 mg plus 5 mg medroxyprogesterone on days 15 to 28.
The Premarin label approves conjugated estrogens for moderate to severe hot flashes and vaginal atrophy due to menopause, low estrogen from hypogonadism, removal of the ovaries or ovarian failure, prevention of osteoporosis after menopause, and, for relief only, some metastatic breast cancers and advanced prostate cancer. For menopause uses it starts most women at 0.3 mg a day, adjusted to the lowest dose that works, every day or in cycles such as 25 days on and 5 days off. The Prempro and Premphase label approves the combination for women with a uterus for hot flashes, vaginal atrophy and osteoporosis prevention; the progestin is there to lower the risk of uterine lining overgrowth from estrogen.
Premarin's boxed warning is titled "Endometrial cancer, cardiovascular disorders, breast cancer and probable dementia", and Prempro's "Cardiovascular disorders, breast cancer, endometrial cancer and probable dementia". Both describe the Women's Health Initiative findings: more strokes and blood clots with estrogen alone, and more blood clots, strokes, heart attacks and invasive breast cancer with estrogen plus medroxyprogesterone. In November 2025 FDA said it is starting to remove the boxed warnings about heart disease, breast cancer and probable dementia from menopause hormone products, but not the endometrial cancer warning for systemic estrogen-alone products. The label versions we read on DailyMed still carry the full boxed warning. Full numbers are on the Premarin side effects, Premarin dosing schedule, missed Premarin dose, Prempro side effects, Prempro dosing schedule and missed Prempro dose pages. Comparisons: Premarin vs estradiol tablets, Prempro vs Activella, Duavee vs Prempro and Climara Pro vs Prempro. Storage: Prempro. Premarin vaginal cream has its own side effects page.
The Premarin label gives, after one 0.625 mg tablet, a time to peak of 6.9 hours and a half-life of 26.7 hours for total estrone (14.8 hours after subtracting the body's own estrone), and 5.6 and 11.4 hours for total equilin. In the Prempro label, medroxyprogesterone peaked at about 2.4 to 2.8 hours with a half-life of about 38 to 46 hours after two combination tablets.
Numbers shown are taken from the source above. Half-life varies from person to person.
How Dose Track handles peptides · Reconstitution calculator · Half-life calculator