Like all medicines, methadone can cause side effects, but many people have no side effects or only minor ones.
You're more likely to get side effects if you are on a high dose of methadone.
Common side effects of methadone
These common side effects of methadone happen to more than 1 in 100 people. There are things you can do to help cope with them:
Constipation
Try to get more fibre into your diet by eating fresh fruit and vegetables and cereals. Drinking several glasses of water or other non-alcoholic liquid each day can help. If you can, it may also help to do some exercise.
If your symptoms do not go away, speak to a pharmacist or doctor about medicine to help prevent or treat constipation caused by methadone.
Feeling or being sick (nausea or vomiting)
This usually wears off after a few days. Talk to your doctor if it carries on for longer.
If you feel sick, try taking your medicine with food. It may also help to avoid rich or spicy food. If you're being sick, try taking small frequent sips of water to avoid dehydration.
Do not take any other medicines to treat vomiting without speaking to a pharmacist or doctor.
If you take the combined contraceptive pill or progestogen-only pill and you're being sick, your contraception may not protect you from pregnancy. Check the pill packet for advice.
Feeling sleepy, tired or dizzy
This usually wears off within a couple of weeks as your body gets used to methadone. Talk to your doctor, key worker or prescriber if these side effects carry on for longer.
Do not drive, cycle or use tools or machines if you're feeling tired or dizzy.
Mild headache
Make sure you rest and drink plenty of fluids. Ask your pharmacist to recommend a painkiller. If headaches are severe or do not go away, talk to your doctor.
Feeling cold and sweating more than usual
Speak to your doctor, key worker or prescriber if this does not go away. They may need to adjust your dose.
Dry eyes, mouth and nose
This usually improves as you get used to methadone.
For dry eyes, ask a pharmacist for advice about eye drops called artificial tears. For a dry mouth, have frequent sips of water or other cold drinks.
Speak to your doctor, pharmacist or key worker if the advice on how to cope does not help and a side effect is still bothering you or does not go away.
Serious side effects
Serious side effects happen in less than 1 in 100 people.
Call 111 now if you're seeing things that are not there (hallucinations), having changes in mood or feeling confused.
Immediate action required: Call 999 if:
- you have any problems breathing
- your heartbeat is irregular, or faster or slower than usual – these can be signs of a heart rhythm problem (arrhythmia)
- you have temporary loss of vision or a constant throbbing headache which gets worse when coughing or straining – this can be due to build-up of pressure around the brain (intracranial hypertension)
Do not drive yourself to A&E.
The person you speak to at 999 will give you advice about what to do.
Serious allergic reaction
It's possible to have a serious allergic reaction to methadone (anaphylaxis), but this is rare.
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.
Do not drive yourself to A&E.
The person you speak to at 999 will give you advice about what to do.
Other side effects
These are not all the side effects of methadone. For a full list, see the leaflet that comes with your medicine.
Reporting side effects
You can report any suspected side effect using the Yellow Card safety scheme.
Visit the Yellow Card website for more information about reporting side effects.