Cancer Home > Precautions and Warnings With Anastrozole

By reviewing precautions and warnings with anastrozole before taking it, you can help ensure a safe and successful treatment process. Women who have osteoporosis or who are breastfeeding may be advised to avoid the drug. Women who are pregnant will be advised not to take it. Precautions and warnings with anastrozole also extend to people who are allergic to any inactive components of the drug.

Anastrozole: What Should I Tell My Healthcare Provider?

You should talk with your healthcare provider prior to taking anastrozole (Arimidex®) if you have:
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 Anastrozole

Warnings and precautions to be aware of prior to taking anastrozole include the following:
  • It is not known if anastrozole is safe and effective for breast cancer treatment in premenopausal women, although it is sometimes used in an off-label fashion for this use.


  • In one study comparing anastrozole with tamoxifen, some women who took anastrozole had a higher risk for heart attack (or other similar cardiac "events") or angina. In particular, the risk was increased in women who already had heart disease. An increased risk (compared to tamoxifen) was not seen for other women.



  • Anastrozole (as well as most medications that decrease the effects of estrogens) can lead to osteoporosis. If you already have osteoporosis (or are at risk for the condition), your healthcare provider may recommend certain lifestyle changes or medication to protect you from fractures (see Osteoporosis Prevention).
  • Anastrozole can interact with other medications (see Drug Interactions With Anastrozole).
  • Anastrozole is considered a pregnancy Category X medication. This means that it is likely to cause harm to a fetus during pregnancy (see Arimidex and Pregnancy).
  • It is not known if anastrozole passes through breast milk. Therefore, if you are breastfeeding or plan to start, discuss this with your healthcare provider prior to taking the drug (see Arimidex and Breastfeeding).
Written by/reviewed by:
Last reviewed by: Kristi Monson, PharmD;
Last updated/reviewed:
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