Short answer: For breast cancer, the generic tamoxifen label gives 20 mg to 40 mg a day, with doses above 20 mg split into morning and evening. It says trial data support 5 years of adjuvant treatment and found no sign that more than 20 mg a day worked better. For DCIS and for reducing breast cancer risk in high-risk women, the dose is 20 mg daily for 5 years.
This is what the FDA label says. Follow your prescriber. Your prescriber may use a different dose or pace than the label's standard schedule.
What Tamoxifen is approved for: This page uses the generic tamoxifen citrate tablets label (Mylan). Tamoxifen is approved to treat metastatic breast cancer in women and men, as adjuvant treatment of node-positive and node-negative breast cancer after surgery, to reduce the risk of invasive breast cancer in women with DCIS after surgery and radiation, and to reduce breast cancer incidence in women at high risk (Indications and Usage).
Source
Tamoxifen Citrate Tablets, USP (generic), prescribing information and Medication Guide. Mylan Pharmaceuticals. DailyMed, version published August 20, 2026. DailyMed setid 7ee3d3d2-85d1-4018-8e70-5ed8a64ae1f0
Tamoxifen tablets are swallowed whole with water or another non-alcoholic liquid, with or without food, every day (Medication Guide).
Daily doses above 20 mg are given in divided doses, morning and evening (Dosage and Administration).
The Medication Guide says it may be easier to remember if taken at the same time each day, and to take it for 5 years unless the doctor says otherwise.
The table below is the label's schedule, from the Dosage and Administration section. Numbers are copied exactly; the section is in brackets.
| Use | Dose | How long |
|---|---|---|
| Breast cancer | 20 mg to 40 mg daily; doses above 20 mg split morning and evening | Trial data support 5 years of adjuvant therapy |
| Ductal carcinoma in situ (DCIS) | 20 mg daily | 5 years |
| Reduction in breast cancer incidence in high risk women | 20 mg daily | 5 years; no data support other than 5 years |
In the EBCTCG 1995 overview, there was no indication that doses greater than 20 mg per day were more effective.
Results of the B-14 study suggest that continuing beyond 5 years does not add benefit, and studies using about 5 years showed greater reductions in recurrence and death than shorter courses.
In the B-14 study, one 10 mg tablet was given twice a day for at least 5 years; in the ECOG, NATO and Toronto trials, one 10 mg tablet was given two or three times a day for 2 years.
For sexually active women who could become pregnant, tamoxifen is started during menstruation; with irregular periods, a negative pregnancy test (B-HCG) just before starting is sufficient.
Women taking it for risk reduction or as adjuvant therapy have a breast exam, mammogram and gynecologic exam before starting, repeated at regular intervals.
Periodic complete blood counts including platelets, and periodic liver function tests, are recommended.
Nonhormonal birth control is used during treatment and for about 2 months after stopping; the Medication Guide says tamoxifen can stop hormonal birth control from working.
If you forget a dose, take it when you remember, then take the next dose as usual. If it is almost time for the next dose, or you remember at the next dose, do not take extra tablets to make up the missed dose.
More on this: missed a dose of Tamoxifen.
In Dose Track you set up Tamoxifen as a protocol with the dose and schedule your prescriber gave you. A protocol can hold dose steps, each with its own dose and length in days or weeks, so a step-up plan like the one on the label can be entered once and the app moves to the next step on its own. Reminders follow the schedule, and every dose is logged with the date and time, so you can see which step you are on and when your last dose was. The app follows what you enter; it does not choose or change a dose.
This page is what the FDA label says, in plain words. It is not medical advice. Follow your prescriber, and ask them or your pharmacist about anything here.