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Side Effects of Aromatase Inhibitors


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If you have hormone receptor-positive breast cancer, hormone therapy with tamoxifen and/or an aromatase inhibitor (such as anastrozole, letrozole and exemestane) is a key part of your treatment.  

Aromatase inhibitors are only used to treat postmenopausal women. Premenopausal women should not take aromatase inhibitors. And, women with certain heart problems should not take the aromatase inhibitor anastrozole.

Side effects of aromatase inhibitors versus side effects of tamoxifen

Although both aromatase inhibitors and tamoxifen can cause menopausal symptoms such as hot flashes and night sweats, they have many different side effects as shown below in Figure 5.11. Your health care provider can help you treat many of these side effects. 


Figure 5.11: Side effects of aromatase inhibitors versus side effects of tamoxifen 
  Aromatase inhibitors  Tamoxifen 
Common side effects 
  • Hot flashes and night sweats
  • Joint and muscle pain
  • Loss of bone mineral density (may lead to osteoporosis or bone fractures)
  • Hot flashes and night sweats
  • Vaginal discharge
  • Vaginal dryness or itching
Uncommon or rare side effects 
  • Carpal tunnel syndrome
  • Hair thinning
  • Heart problems
  • Increased blood pressure
  • Increased cholesterol
  • Mood swings and depression  
  • Loss of sex drive
  • Vaginal bleeding

Very rare:  

  • Blood clots in the large veins (deep vein thrombosis)
  • Blood clots in the lungs (pulmonary emboli)
  • Bone loss (premenopausal women only)
  • Cancer of the lining of the uterus (endometrial cancer)
  • Cancer of the uterus (uterine cancer)
  • Cataracts
  • Stroke  

Adapted from National Cancer Institute materials [67,69-74].


Learn more about the side effects of tamoxifen.

Aromatase inhibitors and joint and muscle pain

Joint pain (arthralgia – ar-THRAL-juh) and muscle pain (myalgia – my-AL-juh) are common side effects of aromatase inhibitors. The pain may be in the hands and wrists, feet and ankles, knees, back or other parts of the body [75-76]. Up to 36 percent of women in clinical trials of aromatase inhibitors have reported joint pain and up to 15 percent have reported muscle pain (other studies have found even higher rates of these side effects) [75-77]. Although aromatase inhibitors can cause joint and muscle pain, they do not cause permanent joint or muscle damage.

If you have joint or muscle pain while taking an aromatase inhibitor, talk to your health care provider. Anti-inflammatory medications (such as aspirin or ibupropin), special exercises or acupuncture may ease the pain [76,78]. Or, your provider may switch you to another aromatase inhibitor (you may have less pain with a different drug) or recommend tamoxifen [77-78].

Aromatase inhibitors and bone health

Aromatase inhibitors cause a loss of bone density, which leads to higher rates of osteoporosis and bone fractures compared to tamoxifen [74]. Some medications may help prevent osteoporosis. Your health care provider may prescribe drugs called bisphosphonates or the drug denosumab to help maintain bone density while you are taking aromatase inhibitors.

You can help strengthen and protect your bones through regular exercise [79]. For example, weight-bearing exercise (exercise that involves standing rather than sitting) and protect bones and lower the risk of hip fractures [80]. Getting enough calcium and vitamin D (your provider can tell you if you are getting enough calcium and vitamin D) and not smoking can also help strengthen your bones [79].

Although mostly a concern for people with metastatic breast cancer who take higher doses of bisphosphonates or denosumab, these drugs can cause severe bone, joint and muscle pain [74,81]. If you have any of these symptoms, report them to your health care provider right away. In rare cases, a serious jaw bone disorder called osteonecrosis may occur. It is important to have a dental exam prior to starting treatment with bisphosphonates [49].

Long-term side effects

More time is needed to assess the long-term risks and benefits of aromatase inhibitors. 

Updated 04/26/13


Aromatase Inhibitors 

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