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How long do side effects last after stopping Arimidex?

Medically reviewed by Carmen Pope, BPharm. Last updated on April 25, 2023.

Official answer

  • Some side effects of Arimidex, such as nausea, hot flashes, pain, chest discomfort, dry eyes, a reduced sex drive, and weakness, should resolve within a few weeks of discontinuing Arimidex.
  • However, some side effects, such as high cholesterol, lymphedema, osteoporosis, and vaginal dryness may persist despite discontinuation of Arimidex.
  • It can also take several weeks or months to reverse bad sleeping habits caused by Arimidex.
  • Talk to your doctor if side effects from Arimidex are persisting despite stopping it.

Arimidex (anastrozole) is a medication that is used to treat breast cancer in postmenopausal women.

In most cases, Arimidex is taken for five years, although some women may take it for a shorter period. Once your treatment team has decided that you can stop taking Arimidex, you can stop it completely; you won’t need to taper down the dose gradually.

There is very good evidence too that Arimidex continues to significantly reduce the risk of developing breast cancer for many years after stopping it, if you have been taking it for five years.

How long do side effects continue once Arimidex is stopped?

Many side effects of Arimidex will improve within a couple of weeks of stopping Arimidex; however, some may persist long term. No new side effects have been reported in clinical trials after stopping Arimidex.

Side effects that should resolve quickly include:

  • Chest discomfort
  • Dizziness
  • Dry eyes
  • Headache
  • Heartburn
  • Hot flashes
  • Nausea
  • Pain
  • Sex drive
  • Weakness.

Side effects that may persist for a few months, or that may still require medications to treat them include:

  • Carpal tunnel syndrome and other nerve-related conditions
  • Dry hair
  • High blood pressure
  • High cholesterol
  • Lymphedema
  • Osteoporosis
  • Sleeplessness (it can take months to resolve bad sleep habits)
  • Vaginal dryness (tends to be the result of vaginal atrophy).

Unfortunately, no formal clinical studies have been done investigating the persistence of side effects from Arimidex.

How long does Arimidex last in your body for?

The half life of Arimidex is 30 to 60 hours. Generally it takes four to five half-lives for a drug to be eliminated from the body, so in the case of Arimidex this would be 150 to 300 hours, or six to 12 days.

What are the side effects of Arimidex?

Side effects may start within a day of starting Arimidex. This is because Arimidex lowers total body estrogen levels by about 70% within 24 hours of starting the drug, which effectively creates an artificial menopause. So side effects similar to those which would happen if you were going through menopause, such as hot flashes or difficulty sleeping.

Other side effects, such as high cholesterol and osteoporosis (brittle bones) take much longer (months to years) to develop and may be hard to notice, but your doctor will monitor you for these.

Some side effects (such as osteoporosis, high cholesterol, high blood pressure) will persist for as long as you take Arimidex, and you may need to take medications for these. Others, such as lack of energy, nausea, and vomiting, and a headache go away within a couple of days to a few weeks. Talk with your doctor if you are having difficulty managing your side effects from Arimidex.

Common side effects of Arimidex that affect more than 5% of women and generally start soon after therapy begins include:

  • Asthenia (weakness or lack of energy)
  • Back, chest, muscle, stomach, or pelvic pain
  • Constipation
  • Cough
  • Diarrhea
  • Headache
  • Hot flashes (flushes)
  • Joint pain
  • Nausea and vomiting
  • Rash
  • Reduced sex drive
  • Sleeplessness
  • Sore joints
  • Sore throat
  • Vaginal dryness.

Other side effects that generally take weeks or months to develop include:

  • Bone pain
  • Carpal tunnel syndrome (a nerve condition that affects your wrist, causing pain, tingling, or numbness)
  • Depression or low mood
  • High blood pressure
  • High cholesterol
  • Osteoporosis (brittle bones) and fractures
  • Shortness of breath
  • Swelling in the ankles and feet (peripheral edema)
  • Swollen lymph nodes (lymphedema
  • Weight loss.

The most common reason for discontinuing Arimidex has been hot flashes, although the incidence of this is less than with tamoxifen.

Serious side effects that occur in less than 1% of women include:

  • Skin reactions, such as lesions, ulcers or blisters
  • Severe allergic reactions with swelling of the face, lips, tongue or throat
  • Liver toxicity, including liver inflammation and changes in liver function tests.

How does Arimidex work?

The growth of many cancers of the breast is stimulated or maintained by estrogens. Arimidex lowers estrogen levels by preventing the synthesis of estrogen from adrenal androgens (primarily androstenedione and testosterone).

It does this by inhibiting the enzyme aromatase, which converts these androgens into estrogen. This slows the growth of tumors that require estrogen to grow. Arimidex is selective too which means that it only affects blood estradiol concentrations, and has no effect on the formation of adrenal corticosteroids or aldosterone.


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