In women who have had their menopause, the main source of oestrogen is through the conversion of androgens (sex hormones produced by the adrenal glands) into oestrogens. This is carried out by an enzyme called aromatase and it happens mainly in the fatty tissues of the body.

Anastrozole is a drug that blocks the aromatase and so reduces the amount of oestrogen in the body.

Possible side effects

Each person's reaction to any medicine is different. Most people have very few side effects with anastrozole, while others may experience more. The side effects described here won't affect everyone and people can have some of them to varying degrees:

Hot flushes and sweats

These are similar to that experienced with the menopause and are usually mild and may wear off after a period of time. Please look at the staying well section- menopause, for advice.

Risk of osteoporosis

Women who have, or are at risk of, osteoporosis (weakened bones) should have their bone strength assessed before and during treatment with anastrozole (DXA bone scan.) Some women may need to take bone-strengthening drugs to help prevent osteoporosis developing. Please look at the ‘staying well section’- osteoporosis, for advice.

Vaginal dryness

Gels that can help to overcome the dryness are available. You can buy these from a chemist or your doctor can prescribe them.

Hair thinning

Some women notice that their hair becomes thinner. This is usually mild and the hair grows back at the end of treatment.

Vaginal bleeding

Some women have some vaginal bleeding, usually in the first few weeks of treatment. This is rare and usually occurs after changing from other hormonal therapies to treatment with anastrozole. If the bleeding continues, tell your doctor or breast care nurse.

Tiredness (fatigue) and lethargy

Some people can have increased tiredness, especially at the start of treatment. It's important to get plenty of rest. If you feel sleepy you should not drive or operate machinery.

Arthralgia – joint pain

This usually starts with morning stiffness and joint discomfort in various sites, including hands, knees, back, hips, and shoulders.

Arthralgia has been shown to begin appearing at approximately 2 months after the start of treatment and to peak at around the 6-month mark. However, it can appear up to 2 years after initiation of therapy. For most people it is mild to moderate and can be coped with.

In at least half of women, the problem usually starts getting better around 6-months from the beginning of treatment. By 18 months, 75% of women have some significant easing of their symptoms.

The most effective treatment is rest, pain killers and gentle massage. See your GP if it is severe for prescription treatments and advice. Once the aromatase inhibitor is stopped, the joint pain will usually go away. It can vary from person to person how long it takes to get back to normal but usually this happens within days to weeks of stopping the drug and not longer than 2-3 months.

Carpal Tunnel syndrome (CTS)

It has been noted that carpal tunnel syndrome is a possible, though usually rare, side-effect for women. Symptoms include dull, aching discomfort in the hand, forearm or upper arm, paraesthesias (numbness) in the hand, weakness or clumsiness of the hand and dry skin, swelling, or colour changes in the hand. A physical examination by the doctor is often sufficient to identify the presence of carpal tunnel syndrome. Nerve tests can confirm the diagnosis or rule out other causes for the problem.

The goal of treatment for CTS is to reduce the swelling and pressure on the median nerve. For most people who develop CTS, proper treatment usually can relieve pain, numbness and tingling, and restore normal function of the wrist and hand.

Always let a doctor or nurse know about any side effects. There are usually ways in which they can be controlled or improved.