9 Tamoxifen Side Effects You Should Know About

Tamoxifen (Soltamox) is a common prescription medication used to treat people living with hormone-receptor positive breast cancer. It can also lower the risk of breast cancer in certain people.

Tamoxifen comes as an oral tablet and liquid, and it belongs to a class of medications known as selective estrogen receptor modulators (SERMs). As a SERM, tamoxifen lowers estrogen activity in some areas of the body — like in breast tissue. But in other areas of the body, like the bones and uterus, tamoxifen mimics estrogen. With its strategic approach, tamoxifen can work to treat and prevent breast cancers that rely on estrogen as fuel to grow.

But, these estrogen changes can lead to side effects. While most side effects are mild and manageable, some can be bothersome. And since tamoxifen is taken for up to 5 to 10 years in some cases, managing side effects is important so you can keep receiving its benefits.

Read on to learn more about nine tamoxifen side effects and how to keep them under wraps.

1. Hot flashes

Hot flashes are a common, and often unpleasant, side effect of tamoxifen. Hot flashes are sudden rushes of heat in your face, neck, or chest. They can also be accompanied by sweating, chills, and feelings of anxiety. Up to 80% of people in tamoxifen’s initial studies experienced hot flashes to some degree. It usually starts happening within the first few months of starting tamoxifen.

Hot flashes happen because tamoxifen lowers estrogen levels in the body, which can affect how well your body can regulate your body temperature. Hot flashes from tamoxifen can also be worsened by stress, alcohol or caffeine, and hot weather.

To help manage hot flashes, you can try natural remedies like wearing loose-fitting, breathable clothing and managing stress. You can also avoid spicy foods, caffeine, and alcohol. Staying well-hydrated and exercising often may also help. 

If hot flashes become too much, talk with your healthcare provider about medications that can help. You could also ask about switching to another hormonal therapy that may cause fewer hot flashes.

2. Vaginal discharge or bleeding

Vaginal discharge is a common side effect of tamoxifen. Up to 55% of women in clinical trials reported it to some degree. Greater vaginal discharge happens because tamoxifen works like estrogen in the vagina, which causes more vaginal secretions. This discharge is usually white or clear and odorless.

These are some ways to manage vaginal discharge:

• Bathe or shower daily using warm water and soap.

• Wear cotton underwear and loose-fitting clothing.

• Use panty liners in your underwear to help absorb discharge.

• Avoid douching or using products that may irritate the vaginal area.

If you experience any bloody discharge or a change in the amount, smell, or appearance of your vaginal discharge, you should let your healthcare provider know right away. Bloody discharge may be a sign of something more serious.

3. Swelling in the arms and legs

Swelling, or peripheral edema, is another common tamoxifen side effect. Swelling can happen in the feet, ankles, and arms. This can also lead to weight gain from excess fluid. Up to 32% of people in clinical trials with tamoxifen reported having some swelling.

To help limit swelling, try elevating your feet and avoid standing for long periods. You can also try lowering the amount of salty or processed foods in your diet.

But, if you also experience a dry cough, shortness of breath, or tightness in your chest, you should let your healthcare provider know. These can be early signs of fluid around your lungs. If swelling becomes painful or severe, you should let your healthcare provider know immediately.

4. Nausea

When you first start taking tamoxifen, you may experience some nausea. About 26% of people taking tamoxifen experienced some nausea in clinical trials. Thankfully, nausea symptoms tend to improve over time as your body gets used to the medication.

To help lower your risk of nausea, you can try taking it with food. You should also try to avoid foods that may make nausea symptoms worse, like greasy, spicy, or acidic foods. You can also try OTC medications, like antacids, and eating bland foods, like broth and saltine crackers. 

If your nausea becomes more bothersome, speak with your healthcare provider about anti-nausea medications. But if it becomes severe or you aren't able to keep fluids down, let your healthcare provider know right away.

5. Menstrual irregularities

Tamoxifen can cause changes to your period. Since tamoxifen blocks estrogen, periods can become irregular, lighter, or they can stop happening altogether. Up to 25% of women taking tamoxifen experienced menstrual irregularities in initial studies.

If you're taking tamoxifen long term, irregular periods may be due to menopause occurring naturally during this time. Or, if you received other medications like chemotherapy, menopause may happen earlier.

Your periods may return to normal after you stop taking tamoxifen.

6. Eye problems

Tamoxifen can sometimes raise your risk of getting cataracts or needing cataract surgery. It's not entirely understood why this happens, but it’s more common among people taking tamoxifen for longer periods of time. But it can happen at any time after starting treatment with tamoxifen and even after you stop taking it.

If you’re taking tamoxifen, you should look out of any changes in your vision, like:

• Clouded or blurry vision

• Trouble seeing at night

• Sensitivity to light

• Seeing halos around lights

Although this is uncommon, you should let your healthcare provider know if you have any changes in your vision. They may want you to see an eye doctor.

7. Skin changes

You might develop a dry and itchy rash while taking tamoxifen. Up to 19% of people taking tamoxifen in initial studies experienced changes in their skin. 

Typically, a rash and dry skin can be relieved by applying non-scented lotion often. Other ways to help avoid dry, itchy skin include:

• Taking shorter showers with warm water instead of hot water

• Using gentle soaps instead of soaps or detergents that may irritate skin

• Wearing loose-fitting clothing

• Using a humidifier in your home

• Staying well hydrated

If you develop a rash that gets worse or is followed by hives, swelling, or blistering skin, let your healthcare provider know right away. This may be a sign of an allergic reaction.

8. Uterine cancer risk

In some cases, tamoxifen has been linked to uterine cancer. Tamoxifen works like estrogen in the uterus, so this can cause changes to the lining of the uterus.

But, it’s not common. In a large clinical trial of about 13,000 people, 33 people who took tamoxifen developed uterine cancer. This is compared to only 14 people who took a placebo (a sugar pill). Some studies have also shown that you may be at a higher risk of developing uterine cancer if you’ve been taking tamoxifen for many years.

Let your healthcare provider know if you have any abnormal bleeding from the vagina or bloody discharge or if you have any new pain or pressure in your lower belly area. These may be signs of uterine cancer. 

Good to know: If you’ve had surgery to remove your uterus, you’re not at risk of developing uterine cancer.

9. Blood clots

You may also be at a higher risk of developing blood clots if you take tamoxifen. Blood clots can possibly happen in your legs (deep vein thrombosis) and can travel to your lungs (pulmonary embolism).

This likely happens because its estrogen effects can affect clotting factors in your blood. You may be at a higher risk of developing a blood clot while taking tamoxifen if you’re also receiving chemotherapy, have a family history of blood clots or coronary artery disease, or are a smoker. Other factors that may raise your risk of clotting include having overweight, high blood pressure, or recent surgery.

To help lower your risk of blood clots while taking tamoxifen, you should stay active and try to get regular exercise, maintain a healthy body weight, and stay well hydrated. Compression socks are also helpful if you’re traveling or sitting for long periods of time.

When should I let my healthcare provider know about tamoxifen side effects?

You should let your healthcare provider know if you have any side effects that are bothersome or you can't tolerate. They can help make your experience with tamoxifen more comfortable.

If you experience any of the following serious side effects, you should contact you healthcare provider right away:

• Abnormal vaginal bleeding

• Changes in your vaginal discharge, or pelvic pain or pressure

• Leg swelling or tenderness, chest pain, or sudden weakness on one side of the body, which may be a sign of a blood clot

• Shortness of breath

• Changes in your vision

Why trust our experts?

Written by:

Sonja Jacobsen, PharmD, BCPS, BCOP

Sonja Jacobsen, PharmD, BCPS, BCOP,  is a clinical oncology pharmacy specialist currently practicing in Seattle. She has been practicing as a pharmacist since 2015 and is licensed to practice in Washington state and North Carolina.

Edited by:

Joshua Murdock, PharmD, BCBBS

Joshua Murdock, PharmD, BCBBS, is a licensed pharmacist in Arizona, Colorado, and Rhode Island. He has worked in the pharmacy industry for more than 10 years and currently serves as a pharmacy editor for GoodRx.

Reviewed by:

Rachel Feaster, PharmD, BCOP, BCPS

Rachel Feaster has over 10 years of professional experience in ambulatory, inpatient, pharmacogenomics, and oncology care. She is board certified in oncology and pharmacotherapy.

Our editorial standards

Meet our experts