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Does anastrozole cause hair loss?

Medically reviewed by Carmen Pope, BPharm. Last updated on May 16, 2024.

Official answer

  • Anastrozole may cause hair thinning or Grade 1 alopecia because of its estrogen lowering effects; however, it is unlikely to cause complete hair loss.
  • Hair thinning due to anastrozole usually improves after the first year of treatment, although some women may experience it for the total duration of treatment.
  • 80% of women experienced moderate to significant improvements in their alopecia after treatment with topical minoxidil 5%.
  • Topical vitamin C products applied to the scalp as well as oral omega-3 and -6 fatty acids may also improve hair health.

Anastrozole is a medication that is used to treat hormone-receptor-positive breast cancer in postmenopausal women. Side effects may start within a day of starting Anastrozole. This is because Anastrozole lowers total body estrogen levels by about 70% within 24 hours of starting the drug, which causes side effects similar to those of menopause, such as hot flashes or difficulty sleeping.

Anastrozole may cause hair thinning because of its estrogen lowering effects; however, it is unlikely to cause complete hair loss. Hair thinning usually improves after the first year of taking anastrozole; although some women may experience thinning for the total duration of treatment.

Research has shown that 92% of women treated with hormone-lowering therapy, such as anastrozole, experienced Grade 1 alopecia (hair loss). This is hair loss of less than 50% of normal for that person and is not noticeable from a distance, only on close inspection. Grade 1 alopecia means a different hairstyle may cover the hair loss, but it does not require a wig or hairpiece to camouflage.

In the same study, 80% of the women who were treated with minoxidil 5% for hair loss caused by hormone-lowering therapy experienced either moderate to significant improvement in their alopecia.

There is also evidence that supplementation with Vitamin C increases the effects of estrogen on the scalp and lowers the effectiveness of testosterone when applied to the scalp in an oil-based preparation that allows the vitamin C to come into contact with the hair.

Oral supplementation of omega-3 and -6 fatty acids has also been shown to protect and improve hair health through antioxidant effects on the scalp tissue.

Both vitamin C and omega-3 and -6 fatty acids are safe to use during breast cancer as long as the maximum dosages are not exceeded.

Talk with your doctor if you are having difficulty managing your side effects from Anastrozole.

How to reduce hair thinning from cancer treatments

Treating your hair gently may help minimize hair thinning:

  • Use a low-sulfate, gentle shampoo or conditioner
  • Wash your hair with lukewarm water only
  • Minimize brushing of hair close to the scalp, try to gently brush the ends only
  • Use a wet brush to gently brush your hair before you wash it
  • Avoid cutting the hair too short as long hair helps to cover small patches of hair loss
  • Avoid hair ties and fasteners, use pins or crocodile clips instead
  • Protect your scalp from the sun
  • Avoid perming or straightening your hair, only use heated rollers or curling wands occasionally
  • If you color your hair use a vegetable-based organic hair color which is more gentle on your hair and scalp
  • Dry your hair naturally or use the cool setting on a hairdryer.

Related Questions

What are the side effects of anastrozole?

Common side effects of anastrozole that affect more than 5% of women and generally start soon after therapy begins to 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
  • 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
  • Hair thinning
  • 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 gain.

The most common reason for discontinuing anastrozole 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 anastrozole work?

The growth of many cancers of the breast is stimulated or maintained by estrogens.

Anastrozole lowers estrogen levels by preventing the synthesis of estrogen from adrenal androgens (primarily androstenedione and testosterone). Anastrozole does this by inhibiting the enzyme aromatase, which converts these androgens into estrogen. This slows the growth of tumors that require estrogen to grow.

Anastrozole is selective too which means that it only affects blood estradiol concentrations, and has no effect on the formation of adrenal corticosteroids or aldosterone.

  • Hair loss during breast cancer treatment. Breast cancer Network Australia. Sept 2016.
  • Karatas F, Sahin S, Sever AR, Altundag K. Management of hair loss associated with endocrine therapy in patients with breast cancer: an overview. Springerplus. 2016;5:585. Published 2016 May 10. doi:10.1186/s40064-016-2216-3
  • Anastrozole

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