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Arimidex Doesn’t Seem to Cause Thinking or Memory Problems

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A small study found that postmenopausal women diagnosed with hormone-receptor-positive, early-stage breast cancer who took the aromatase inhibitor Arimidex (chemical name: anastrozole) were no more likely than women who got a placebo to have memory or thinking problems in the 2 years after starting Arimidex.

About half of the 207 women in the study took Arimidex after surgery to remove the breast cancer. The other half of the women received a placebo (a "dummy" or sugar pill) after surgery. Many of the women in the study also received radiation therapy and chemotherapy after surgery.

All of the women had cognitive testing -- tests that measure memory and thinking skills -- three times during the study:

  • at the start of the study
  • 6 months after starting Arimidex or the placebo
  • 2 years after staring Arimidex or the placebo

During the 6-month and 2-year cognitive tests, the women also reported whether they felt their ability to remember and concentrate had declined.

Before starting Arimidex or the placebo, about a quarter of the women -- 20 women scheduled to take Arimidex and 24 women scheduled to take the placebo pill -- had cognitive test scores that suggested some problems with memory and thinking. These thinking and memory problems couldn't have been caused by Arimidex because the treatment hadn't started yet. A number of other factors related to breast cancer may have caused the thinking and problems, including the physical and emotional stress of being diagnosed and treated, anesthesia used during surgery, or chemotherapy.

Six months after treatment started, a few more women had cognitive test scores that indicated thinking and memory problems:

  • 24 women taking Arimidex (four more than the first baseline test)
  • 27 women taking the placebo pill (three more than the first baseline test)

This slight increase was basically the same whether the women were taking Arimidex or the placebo. So the 6-month results suggested that Arimidex didn't cause thinking and memory problems.

The cognitive tests done 2 years after treatment started showed that fewer women had cognitive test scores that indicated thinking and memory problems compared to the first baseline test:

  • 17 women taking Arimidex (three fewer than the baseline test)
  • 23 who started on the placebo pill (one fewer than the baseline test)

The number of women with abnormal cognitive test results were very similar whether the women were taking Arimidex or the placebo pill. So the 2-year results also suggested that Arimidex doesn't cause thinking and memory problem.

The researchers analyzed the self-reported memory and concentration problems and there weren't any real differences between the women who got Arimidex compared to the women who got the placebo pill. A small number of women in both groups reported problems, but the problems tended to get better over time.

At 6 months:

  • 13 women taking Arimidex and 13 women taking the placebo pill reported memory problems; seven women taking Arimidex and 11 women taking the placebo pill reported concentration problems.

At 2 years:

  • three women taking Arimidex and five women taking the placebo pill reported memory problems; two women taking Arimidex and two women taking the placebo pill reported concentration problems.

While this study didn't show that Arimidex caused any thinking and memory problems, this was a small study and the women were only followed for 2 years. Some of the women in the study also got chemotherapy, which IS associated with thinking and memory problems (known as chemobrain or chemofog). Also, this study only looked at one aromatase inhibitor, Arimidex. It's not clear if these results would apply to the two other aromatase inhibitors: Aromasin (chemical name: exemestane) and Femara (chemical name: letrozole).

Hormonal therapy medicines are used after initial breast cancer treatment to lower the risk of the breast cancer coming back and are usually given for 5 years. While this study suggests that Arimidex doesn't cause memory and thinking problems, aromatase inhibitors and tamoxifen, another hormonal therapy, can cause bothersome side effects. Tamoxifen (which works differently than aromatase inhibitors) can cause hot flashes. Aromatase inhibitors also can cause hot flashes as well as muscle and joint pain. In this research, 30% of the women who took Arimidex reported hot flashes, compared to only 15% of the women who took the placebo pill.

If you're worried about the side effects of hormonal therapy or are currently having troubling side effects, talk to your doctor about how best to manage them. You may be able to take a different hormonal therapy medicine. If you're taking hormonal therapy medicine now, stick with it as prescribed. If you're thinking of stopping early or not starting a treatment because you're afraid of side effects, talk to your doctor first. Together, you can find a solution that is best for YOU.

For more information, visit the Staying on Track with Hormonal Therapy page. You can read about why it's so important to stick to your treatment plan, as well as ways to manage side effects.

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