How much does tamoxifen build up with daily dosing?

At steady state on a daily schedule, the model's level is about 9.17 times what one dose gives, and it swings about 1.1:1 between the peak and the trough before the next dose. Longer gaps between doses mean less build-up and a bigger swing.

Is this chart my actual tamoxifen level?

No. It is a modeled estimate from a published half-life, using the same one-compartment model as the Dose Track app. Real levels vary with body weight, food, kidney and liver function and other factors, and only a lab test measures them. It is not medical advice.

Tamoxifen Half-Life: Peak and Steady State Chart

Q: When does tamoxifen peak after a dose?

Blood levels peak about 5 hours after a dose by mouth, according to Tamoxifen citrate tablets (Mylan) label. Individual timing varies with food, the amount and the person.

Q: How long does tamoxifen take to reach steady state?

About 30 days (~4.3 weeks) of regular dosing at the same amount and interval, which is 5 half-lives. With a half-life of about 6 days, levels reach about 50% of steady state after 6 days and about 90% after 19.9 days. Changing the dose or interval starts a new climb toward a new steady state.

Q: How long does tamoxifen stay in your system after the last dose?

Roughly 5 half-lives, about 30 days (~4.3 weeks), until about 97% has cleared in the model. Half is gone about 6 days after levels start falling. Real clearance varies from person to person, and a drug can still have effects after levels are low.

Short answer: Tamoxifen has a half-life of about 6 days (Tamoxifen citrate tablets (Mylan) label) and reaches steady state after about 30 days (~4.3 weeks) of regular dosing. Levels peak about 5 hours after a dose by mouth. On a daily schedule the model builds up to about 9.2× a single dose, with a peak-to-trough swing of about 1.1:1.

What do tamoxifen levels look like with daily dosing?

The tamoxifen label dose for DCIS and breast cancer risk reduction is 20 mg once daily; the label says steady state takes about 4 weeks. Use in men on TRT is off-label. Source: Tamoxifen citrate tablets (Mylan) label. Bioavailability 90% as in the app. Dashed line: 5 half-lives. Change the amount or schedule in the calculator.

When does tamoxifen peak after a dose?

Levels peak about 5 hours after a dose by mouth.

How long does tamoxifen take to reach steady state?

With regular dosing at a fixed amount and interval, levels climb toward steady state by the same fraction every half-life, whatever the dose. At a half-life of about 6 days:

Time from the first dose to each share of steady state, tamoxifen (half-life 6 days).
Share of steady state	Half-lives	Time
50%	1	6 days
75%	2	12 days
90%	3.3	19.9 days
97% (Dose Track's steady-state rule)	5	30 days (~4.3 weeks)

How much do tamoxifen levels swing between doses?

The longer the gap between doses compared with the half-life, the bigger the swing from peak to trough and the less the levels build up. These ratios do not depend on the amount.

Steady-state peak:trough and build-up by dosing interval, tamoxifen, in Dose Track's model.
Interval	Peak : trough	Build-up vs one dose
Daily	1.1 : 1	9.17×
Every other day	1.23 : 1	4.85×
Twice weekly	1.46 : 1	3.01×
Weekly	2.19 : 1	1.8×
Every 2 weeks	4.9 : 1	1.25×

Build-up is the accumulation ratio 1 / (1 − e^−k·τ), with k = ln 2 / half-life and τ the interval.

How long does tamoxifen stay in your system?

After the last dose, about half is gone every 6 days. After 5 half-lives, about 30 days (~4.3 weeks), roughly 97% has cleared in the model.

Where do these numbers come from?

The FDA tamoxifen label says levels fall in two phases, with a terminal elimination half-life of about 5 to 7 days; Dose Track uses 6 days. Its main active metabolite, N-desmethyl tamoxifen, has a half-life of about 14 days, and steady state takes about 4 weeks for tamoxifen and about 8 weeks for the metabolite. After a single 20 mg dose, peak levels came about 5 hours later; Dose Track uses 5 hours.

Tamoxifen citrate tablets (Mylan) prescribing information: clinical pharmacology, indications and dosage. DailyMed, 2026.

The curve uses the half-life, time to peak, route and bioavailability built into the Dose Track app for tamoxifen, and the same one-compartment model with first-order absorption. These are modeled estimates from published half-lives, drawn with the same one-compartment model as the Dose Track app. Real levels vary from person to person, and only a lab test measures them. This is not medical advice and not a dosing recommendation; dosing decisions belong with you and your prescriber.

Vial sizes and syringe math are in the Tamoxifen Citrate guide.

When does tamoxifen peak and reach steady state?