Short answer: In the NSABP B-14 trial of women after breast cancer surgery, the most common tamoxifen side effects vs placebo were hot flashes (64% vs 48%), fluid retention (32% vs 30%), vaginal discharge (30% vs 15%), nausea (26% vs 24%) and irregular periods (25% vs 19%). The label has a boxed warning about uterine cancers, stroke and pulmonary embolism for women using it to reduce breast cancer risk or after DCIS.
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
WARNING: For Women with Ductal Carcinoma in Situ (DCIS) and Women at High Risk for Breast Cancer
When tamoxifen is used to reduce breast cancer risk in high-risk women or women with DCIS, serious and life-threatening events include uterine cancers, stroke and pulmonary embolism, and some were fatal. In the NSABP P-1 trial, endometrial cancer occurred at 2.20 per 1,000 women-years on tamoxifen vs 0.71 on placebo, stroke at 1.43 vs 1.00, and pulmonary embolism at 0.75 vs 0.25. The label says the benefits outweigh the risks in women already diagnosed with breast cancer.
These are the label's own numbers from the Adverse Reactions section. Where the label compares with placebo (a dummy treatment), both columns are shown, so you can see how much more often a reaction happened on Tamoxifen.
| Adverse Effect | Tamoxifen (n = 1,422) % of Women | Placebo (n = 1,437) % of Women |
|---|---|---|
| Hot Flashes | 64 | 48 |
| Fluid Retention | 32 | 30 |
| Vaginal Discharge | 30 | 15 |
| Nausea | 26 | 24 |
| Irregular Menses | 25 | 19 |
| Weight Loss (> 5%) | 23 | 18 |
| Skin Changes | 19 | 15 |
| Increased SGOT | 5 | 3 |
| Increased Bilirubin | 2 | 1 |
| Increased Creatinine | 2 | 1 |
| Thrombocytopenia | 2 | 1 |
| Deep Vein Thrombosis | 0.8 | 0.2 |
| Pulmonary Embolism | 0.5 | 0.2 |
| Superficial Phlebitis | 0.4 | 0 |
Women with axillary node-negative breast cancer were randomized to 5 years of tamoxifen 20 mg/day or placebo after surgery; mean follow-up about 6.8 years. Thrombocytopenia means a platelet count below 100,000/mm3. The last three rows are the thrombotic events.
| Adverse event | Tamoxifen % of Women | Placebo % of Women |
|---|---|---|
| Hot Flashes | 80 | 68 |
| Vaginal Discharges | 55 | 35 |
| Vaginal Bleeding | 23 | 22 |
| Platelets decreased | 0.7 | 0.3 |
| Mood | 11.6 | 10.8 |
| Infection/Sepsis | 6 | 5.1 |
| Constipation | 4.4 | 3.2 |
| Alopecia | 5.2 | 4.4 |
| Skin | 5.6 | 4.7 |
| Allergy | 2.5 | 2.1 |
The NSABP P-1 trial gave tamoxifen (N = 6,681) or placebo (N = 6,707) to women at high risk for breast cancer. Only events more common on tamoxifen are shown. Symptoms came from quality-of-life questionnaires (6,441 vs 6,469 women), platelets from follow-up forms, and other toxicities from adverse drug reaction forms.
In P-1, severe hot flashes occurred in 45% on tamoxifen vs 28% on placebo, and severe vaginal discharge in 12.3% vs 4.5%. 15% on tamoxifen and 9.7% on placebo withdrew for medical reasons, including hot flashes (3.1% vs 1.5%).
In B-14, thrombotic events through 5 years were 1.7% on tamoxifen vs 0.4% on placebo; two tamoxifen patients with thrombotic events died. In the ECOG trial, hot flashes were 19% vs 8% on placebo and low platelets 10% vs 3%.
In premenopausal women with metastatic breast cancer compared with ovarian ablation (n = 104 vs 100), flushing occurred in 33% vs 46%, missed periods in 16% vs 69%, and altered periods in 13% vs 5%.
In P-1, invasive endometrial cancer occurred in 33 women on tamoxifen vs 14 on placebo, pulmonary embolism in 18 vs 6, deep vein thrombosis in 30 vs 19, stroke in 34 vs 24, cataracts in 540 vs 483 and cataract surgery in 101 vs 63. Uterine sarcoma was 0.17 vs 0.04 per 1,000 women-years in long-term follow-up.
In men with breast cancer, the label says the safety profile appears similar to women, and loss of libido and impotence have led some men to stop treatment.
The Warnings and Precautions part of the label lists these. Each line gives the label's heading and what it means in plain words.
Uterine cancer. Uterine cancers, mostly endometrial adenocarcinoma and rarely uterine sarcoma, are more common with tamoxifen, and some have been fatal. Abnormal vaginal bleeding is evaluated promptly, and annual gynecological exams are advised for current and past users.
Non-cancer uterine changes. Endometrial hyperplasia and polyps are more common. Endometriosis, fibroids, ovarian cysts, irregular periods and missed periods have also been reported.
Blood clots and stroke. Deep vein thrombosis and pulmonary embolism are more common, and more so with chemotherapy. In P-1, pulmonary embolism had a relative risk of 3.01 vs placebo, and three were fatal. Stroke was also increased, though not statistically significant.
High calcium in bone metastases. High blood calcium has been reported within a few weeks of starting in some patients with breast cancer that has spread to bone; tamoxifen is stopped if it is severe.
Liver effects. Liver enzyme changes and, rarely, fatty liver, cholestasis, hepatitis and liver necrosis have been reported, a few fatal. Three liver cancers were reported in a Swedish trial using 40 mg/day vs one in the untreated group.
Eye effects. Corneal changes, reduced color vision, retinal vein clots and retinopathy have been reported, along with more cataracts and cataract surgery.
Pregnancy. Tamoxifen may harm an unborn baby. Women should not become pregnant while taking it or within 2 months after stopping, and use barrier or nonhormonal birth control. The label says tamoxifen does not cause infertility.
Blood counts. Lower platelet counts, low white cells and, rarely, severe neutropenia or pancytopenia have been reported. Periodic blood counts and liver tests are recommended.
Blood thinners and other drugs. With coumarin-type blood thinners such as warfarin, the anticoagulant effect can rise sharply, so prothrombin time is monitored. Tamoxifen should not be given with anastrozole.
Who should not take it for risk reduction. Women who need coumarin-type blood thinners or have a history of deep vein thrombosis or pulmonary embolism must not use it to reduce breast cancer risk or after DCIS. Anyone allergic to tamoxifen must not take it.
From the Medication Guide that comes with Tamoxifen:
Dose Track has a side-effect log. Each entry records the symptom, a severity (none, mild, moderate, severe or life-threatening), the date and an optional note, and can be tied to a specific dose or logged on its own. The history screen shows what you logged over time, which makes it easier to tell your prescriber when a reaction started and whether it is easing. The app records what you enter; it does not judge whether a symptom is serious. For anything on the label's call-your-doctor list, call your doctor.
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.