Like all medicines, memantine can cause side effects, although not everyone gets them.
Side effects are less likely to happen if your doctor gradually increases your dose over at least a month.
Common side effects
These common side effects of memantine happen in more than 1 in 100 people. There are things you can do to help cope with them:
Headache
Make sure you rest and drink plenty of fluids. Ask a pharmacist to recommend a painkiller. Talk to your doctor if your headaches last longer than a week or are severe.
Constipation
Try to get more fibre into your diet such as fresh fruit and vegetables and cereals. Drinking several glasses of water or other non-alcoholic liquids each day can also help. If you can, it may also help to do some gentle exercise.
It's safe to use a laxative if your constipation does not go away. Check with a pharmacist or doctor which laxative would be best for you.
Feeling sleepy and dizzy
Try taking your medicine at night. If you have to take it during the day and feel dizzy or tired, do not drive or ride a bike until you feel better, and fully alert and awake.
Talk to a doctor if these effects bother you or do not get better.
Serious side effects
Call a doctor or call 111 straight away if:
- the whites of your or eyes turn yellow, or your skin turns yellow, although this may be less obvious on black or brown skin, or if you have pale poo and dark pee – these can be signs of liver problems
- you get swollen ankles and legs, become breathless after activity or at rest, feel tired most of the time and find exercise exhausting, develop a persistent cough or a fast heart rate – these can be signs of heart failure
- you have hallucinations (hearing, seeing, smelling or tasting things that feel real but are not real) – this could be a sign of psychosis
- you get a sudden, severe pain in the centre of your stomach, feel sick or start to be sick, get diarrhoea or a high temperature – these can be signs of pancreatitis
- you get a throbbing or cramping pain, swelling, redness and warmth in your leg or arm – these can be signs of a blood clot
Immediate action required: Call 999 or go to A&E if you:
- or the person you're caring for, has a seizure or fit
- get a sharp chest pain (which may get worse when you breath in)
- have sudden breathlessness, difficulty breathing or coughing up blood – these can be signs of a blood clot in your lung
Serious allergic reaction
In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to memantine.
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.
Other side effects
These are not all the side effects of memantine. For a full list, see the leaflet inside your medicine packet.
You can report any suspected side effect using the Yellow Card safety scheme.