Like all medicines, anastrozole can cause side effects, although not everyone gets them.
Common side effects
Anastrozole can cause symptoms similar to the menopause such as hot flushes, difficulty sleeping, tiredness and low mood, but these usually improve during the first months of taking it.
However, if the symptoms are severe or last longer than a few months, talk to your doctor or breast cancer nurse.
These common side effects of anastrozole happen in more than 1 in 100 people. There are things you can do to help cope with them:
Hot flushes and sweating
Try cutting down on spicy food, caffeine, smoking and alcohol. It may help to keep the room cool and use a fan. Try spraying your face with cool water or sipping a cold drink.
Dry or itchy vagina
Ask your doctor or breast cancer nurse to recommend a vaginal moisturiser for treating irritation or dryness.
Talk to your doctor if these symptoms first appear more than a few weeks after you start taking anastrozole.
Bleeding from your vagina
Vaginal bleeding usually happens in the first few weeks after starting anastrozole. Talk to your doctor if it lasts longer than a few days.
Also talk to your doctor if you first get vaginal bleeding more than a few weeks after you start taking anastrozole.
Difficulty sleeping
Avoid caffeine (such as tea, coffee, cola, energy drinks and chocolate) in the afternoon and evening. Keep your bedroom dark and quiet, and try going to bed and getting up at a set time each day.
It may also help to stop watching TV, looking at your mobile phone or using other electronic devices (like tablets), at least 1 hour before bedtime.
Feeling very tired
Gentle exercise and eating healthily can help make you feel less tired. Try going to bed and getting up at a set time each day.
Do not drive, ride a bike or use tools or machinery if you feel very tired while taking anastrozole.
This will usually start to improve as your body gets used to the medicine. Speak to your doctor if it does not get better.
Feeling or being sick
Stick to simple meals and do not eat rich or spicy food. It might help to take anastrozole after you've eaten.
If you're being sick, have small, frequent sips of water to avoid dehydration. Signs of dehydration include peeing less than usual or having dark strong-smelling pee.
Talk to your doctor if your symptoms do not improve or get worse.
Losing your appetite
It might help to take anastrozole after you've eaten.
Eat when you would usually expect to be hungry. If it helps, eat smaller meals throughout the day rather than big meals. Snack when you're hungry. Have nutritious snacks that are high in calories and protein, such as dried fruit and nuts.
Mild aches in your muscles and bones
Ask a pharmacist to recommend a suitable painkiller. If the pain does not go away ask your doctor for advice.
If you have a sudden attack of pain in a joint ask a doctor for advice urgently. Anastrozole can make your bones weaker and there is an increased risk of osteoporosis or bone injuries.
Numb or tingling hands
Ask your doctor for advice if you get this side effect.
Changes to your skin, including a mild rash
Your doctor may suggest using a steroid cream or taking an antihistamine. You can buy these at a pharmacy without a prescription. Check with a pharmacist to see what type is suitable for you.
Hair loss or thinning hair
Some people find that their hair gets thinner when they start taking anastrozole. This is usually mild. Ask your breast cancer nurse for advice if this is bothering you.
Low mood or depression
It's difficult to know whether this is due to the medicine, dealing with menopause symptoms or dealing with being diagnosed with cancer.
Speak to your doctor or specialist nurse. They may recommend therapies, like cognitive behavioural therapy or mindfulness, or antidepressant medicines.
Talk to your doctor or a pharmacist if this advice on how to cope does not help and these side effects bother you or do not go away.
Serious side effects
Serious side effects are rare and happen in less than 1 in 100 people.
Call a doctor or call 111 now if:
- your muscles feel weak, or the joints or tendons in your ankles, legs, shoulders or arms feel weak, painful or swollen
- the whites of your eyes turn yellow, or your skin turns yellow although this may be less obvious on brown or black skin – this can be a sign of liver problems
- you're feeling thirsty and peeing a lot, feeling sick and have lost your appetite – you may need a blood test to check your calcium levels
- you get red or purple spots (if you have light skin) or dark spots (if you have brown or black skin), painful joints, stomach ache, or pain in your side (below your ribs), lower back or around your genitals – these can be signs of Henoch-Schönlein purpura, a condition causing inflammation of your blood vessels
Immediate action required: Call 999 or go to A&E if:
- you have sudden weakness or if you lose feeling in any part of your body, if your face drops on 1 side or you have difficulty speaking – these can be signs of a stroke
- you have very sudden chest pain – this can be a sign of a heart attack
Serious allergic reaction
In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to anastrozole.
Immediate action required: Call 999 now if:
- your lips, mouth, throat or tongue suddenly become swollen
- you're breathing very fast or struggling to breathe (you may become very wheezy or feel like you're choking or gasping for air)
- your throat feels tight or you're struggling to swallow
- your skin, tongue or lips turn blue, grey or pale (if you have black or brown skin, this may be easier to see on the palms of your hands or soles of your feet)
- you suddenly become very confused, drowsy or dizzy
- someone faints and cannot be woken up
- a child is limp, floppy or not responding like they normally do (their head may fall to the side, backwards or forwards, or they may find it difficult to lift their head or focus on your face)
You or the person who's unwell may also have a rash that's swollen, raised, itchy, blistered or peeling.
These can be signs of a serious allergic reaction and may need immediate treatment in hospital.
Long-term side effects
Anastrozole is generally safe to take for a long time. However, it can make your bones weaker and more likely to break (osteoporosis).
You may have bone density (DEXA) scans to check how strong your bones are, before you start taking anastrozole, 1 or 2 years into treatment, and again after you finish your treatment.
Your doctor may recommend a type of medicine called a bisphosphonate to help make your bones stronger. They can also give you advice on exercise and diet to help keep your bones strong.
Anastrozole can also increase your cholesterol levels. Your doctor will monitor this during your regular check-ups and recommend treatment if you need it.
Other side effects
These are not all the side effects of anastrozole. For a full list, see the leaflet inside your medicines packet.
You can report any suspected side effect using the Yellow Card safety scheme.