Breast Cancer Home > Precautions and Warnings With Tamoxifen

An awareness of precautions and warnings with tamoxifen can help ensure a safe, successful treatment process. For example, the medication can cause serious side effects, such as uterine cancer or blood clots. Eye problems are also possible, including cataracts and changes in vision. Precautions and warnings with tamoxifen also extend to those who are allergic to components used to make the drug or who have high calcium levels.

Tamoxifen: What Should I Tell My Healthcare Provider?

You should talk with your healthcare provider prior to taking tamoxifen citrate (Nolvadex®) if you have:
  • Unexplained vaginal bleeding
  • A history of blood clots or stroke
  • Any allergies, including allergies to food, dyes, or preservatives.
Also, let your healthcare provider know if you are:
  • Pregnant or thinking of becoming pregnant
  • Breastfeeding.
Make sure to tell your healthcare provider about all the medicines you take, including prescription and non-prescription medicines, vitamins, and herbal supplements.

Specific Precautions and Warnings With Tamoxifen

Warnings and precautions to be aware of prior to taking tamoxifen include the following:
  • The medication can cause serious side effects, including blood clots, strokes, or uterine cancer. For some women, the risks of using tamoxifen to prevent breast cancer may outweigh any possible benefits. Be sure to talk to your healthcare provider about the benefits and risks of using the drug in your particular situation.
  • Tamoxifen can cause high calcium levels in the body if given to people with bone metastases (spreading of the cancer to bone). If your calcium levels are extremely high, your healthcare provider may recommend that you stop taking the medication.
  • Tamoxifen can increase the risk of uterine cancer. If you are taking the drug (or have taken it in the past), tell your healthcare provider right away if you have signs of uterine cancer, such as:
    • Changes in your menstrual period
    • Abnormal vaginal bleeding
    • Changes in vaginal discharge
    • Pelvic pain or pressure.
  • The medication may also increase the risk of non-cancerous uterine or ovarian problems, such as uterine fibroids, endometriosis, or ovarian cysts.
  • Tamoxifen can increase the risk of blood clots and strokes. If you have had a blood clot or stroke in the past, tamoxifen may not be the best choice for you.
  • There have been reports of liver problems in people taking tamoxifen. These problems include liver cancer, cirrhosis, and hepatitis. If you already have liver problems, talk to your healthcare provider before taking the drug.
  • Tamoxifen can cause eye problems, including cataracts, vision changes, and other problems. Let your healthcare provider know if you notice any changes in your eyes or vision while taking the drug.
  • Tamoxifen can interact with other medications (see Drug Interactions With Tamoxifen).
  • Tamoxifen is considered a pregnancy Category D medication. This means that it is likely to cause harm to a fetus during pregnancy. Talk to your healthcare provider about the risks and benefits of taking the drug while pregnant (see Tamoxifen and Pregnancy).
  • It is not known if the medication passes through breast milk. Therefore, if you are breastfeeding or plan to start, discuss this with your healthcare provider prior to taking it (see Tamoxifen and Breastfeeding).
Written by/reviewed by:
Last reviewed by: Kristi Monson, PharmD;
Last updated/reviewed:
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