An aromatase inhibitor for breast cancer
Anastrozole
An aromatase inhibitor that lowers oestrogen, used for hormone-receptor-positive breast cancer after the menopause.
What is Anastrozole?
Anastrozole is an aromatase inhibitor. It lowers the amount of oestrogen in the body, which slows or stops the growth of breast cancers that are fuelled by oestrogen. It is used in postmenopausal women with hormone-receptor-positive breast cancer, often for several years, and is also used to help prevent breast cancer in some women at high risk.
Education and reference only. This is a plain-language guide to Anastrozole — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Anastrozole is an aromatase inhibitor used to treat hormone-receptor-positive breast cancer in women who have been through the menopause. It is also used to help prevent breast cancer in some postmenopausal women at increased risk. It is taken as a daily tablet, usually for several years, as part of long-term hormone therapy. It is only suitable after the menopause, when the ovaries are no longer the main source of oestrogen.
How it works
After the menopause, the body still makes small amounts of oestrogen by converting other hormones using an enzyme called aromatase, mostly in fat and other tissues. Many breast cancers grow faster when oestrogen is present. Anastrozole blocks aromatase, sharply reducing the amount of oestrogen in the body. With less oestrogen available, hormone-sensitive breast cancer cells are starved of the signal they need to grow.
Company & origin
Originated / developed by: Originally developed by AstraZeneca and now widely available as a generic medicine..
An aromatase inhibitor introduced in the 1990s for hormone-receptor-positive breast cancer in postmenopausal women.
Practical use
How to take Anastrozole
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take one tablet once a day, ideally at about the same time, with or without food.
- Swallow the tablet whole with a drink of water.
- Keep taking it for the full course your team recommends, often several years, even when you feel well.
- Tell your team about troublesome joint pain or hot flushes, as there are ways to help.
- If you miss a dose, take it when you remember unless your next dose is near, then skip it — never take two together.
Weighing it up
Advantages & disadvantages of Anastrozole
Advantages
- Reduces the risk of hormone-sensitive breast cancer returning after the menopause.
- Taken as a simple once-a-day tablet and available as a generic medicine.
- Does not carry the small risk of womb cancer or blood clots seen with tamoxifen.
Disadvantages
- Commonly causes joint and muscle aches and stiffness, which some women find hard to tolerate.
- Lowers oestrogen, which can weaken bones and increase the risk of osteoporosis.
- Can cause hot flushes, vaginal dryness and reduced sex drive.
Practical use
Good to know
Anastrozole is taken once a day, usually for several years, to lower the chance that breast cancer comes back. It works by reducing oestrogen, so it is only used after the menopause. Joint and muscle aches and hot flushes are common, and because lower oestrogen can weaken bones, bone strength is monitored and protective steps may be advised. It is important to keep taking it as prescribed, as the protective benefit builds over time.
Who should not take it / use with caution
- Women who have not yet been through the menopause, as it does not control oestrogen made by working ovaries.
- Women who are pregnant or breastfeeding.
- Anyone who has had a serious allergic reaction to anastrozole.
Monitoring
- Bone-density scans to check for thinning of the bones, with calcium and vitamin D or other treatment if needed.
- Review of joint pain, hot flushes and other side effects.
- Regular breast-cancer follow-up appointments.
Side effects
- Joint and muscle pain or stiffness, and hot flushes.
- Vaginal dryness, reduced sex drive, tiredness and mood changes.
- Thinning of the bones (osteoporosis) over time, with a higher risk of fractures.
Key interactions
- Medicines containing oestrogen (including some HRT) work against it and should not be taken alongside it.
- Tamoxifen can reduce its effect, so the two are not normally combined.
- Tell your team about all medicines and supplements, including anything bought over the counter.
Available as: Tablets.
Answers
Anastrozole: frequently asked questions
Why is anastrozole only used after the menopause?
Before the menopause, the ovaries make large amounts of oestrogen that anastrozole cannot control. After the menopause, oestrogen comes mainly from the aromatase enzyme in other tissues, which anastrozole blocks effectively. For women who have not yet reached the menopause, other treatments such as tamoxifen are used instead.
Why does anastrozole cause joint pain?
Lowering oestrogen can lead to aches and stiffness in the joints and muscles, which is one of the most common side effects. Gentle exercise, painkillers your team recommends, and staying active can help. If the pain is severe or stops you taking it, tell your team, as alternatives exist.
Will anastrozole affect my bones?
Because it reduces oestrogen, which helps keep bones strong, it can lead to thinning of the bones over time. Your team will usually check your bone density and may advise calcium, vitamin D, weight-bearing exercise or bone-protecting medicine.
How long will I need to take anastrozole?
It is usually taken for several years, as the protection against the cancer returning builds over time. Your team will tell you how long is right for you and may sometimes switch you between hormone treatments. Keep taking it as prescribed even if you feel well.
Is anastrozole the same as Arimidex?
Yes — Arimidex is a brand name and anastrozole is the active-ingredient (generic) name. They contain the same medicine, and generic anastrozole works in the same way.
The wider class
About Aromatase inhibitors
Anastrozole belongs to the aromatase inhibitors class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
Browse by body system
Authoritative sources
- BNF: Anastrozole.
- electronic Medicines Compendium (SmPC): Arimidex (anastrozole).
- NICE CKS: Anastrozole.
Building a medicines information resource?
We create evidence-led, dose-free drug and formulary references for teams.