Like all medicines, gabapentin can cause side effects, although not everyone gets them.
Common side effects
These common side effects of gabapentin may happen in more than 1 in 100 people. They're usually mild and go away by themselves.
There are things you can do to help cope with them:
Feeling sleepy, tired or dizzy
As your body gets used to gabapentin, these side effects should wear off. If they do not wear off within a week or two, your doctor may reduce your dose or increase it more slowly. If that does not work, your doctor may suggest a different medicine.
Feeling sick (nausea)
Take gabapentin with or after a meal or snack. It may also help if you do not eat rich or spicy food. Take small sips of water or other fluids to avoid dehydration. Signs of dehydration include peeing less than usual or having dark, strong-smelling pee.
Being sick (vomiting)
Take small sips of water or other fluids to avoid dehydration. Signs of dehydration include peeing less than usual or having dark, strong-smelling pee. Do not take any other medicines to treat vomiting without speaking to a pharmacist or doctor.
If you take the combined contraceptive pill or the progestogen-only pill and you're being sick, your contraception may not protect you from pregnancy. Check the pill packet for advice
Diarrhoea
Drink plenty of water or other fluids to avoid dehydration. Signs of dehydration include peeing less than usual or having dark, strong-smelling pee. Do not take any other medicines to treat diarrhoea without speaking to a pharmacist or doctor.
If you take the combined contraceptive pill or the progestogen-only pill and you have severe diarrhoea for over 24 hours while taking gabapentin, your contraception may not protect you from pregnancy. Check the pill packet for advice.
Mood changes
If you feel this medicine is causing mood changes, talk to your doctor. They may be able to change you to a different medicine.
Swollen arms and legs
Try sitting with your feet raised and try not to stand for a long time. Gently exercising your arms might help. Talk to your doctor if this does not get better.
Blurred vision
Avoid driving, cycling or using tools or machinery while this is happening. If it lasts for more than a couple of days, speak to your doctor as they may need to change your treatment.
Dry mouth
Try chewing sugar-free gum or sucking sugar-free sweets.
Difficulty getting an erection
Speak to your doctor. They may be able to change your medicine or offer other treatments that might help with this problem.
Weight gain
Gabapentin can make you hungrier, so it can be hard to stop yourself putting on weight. Try to eat a healthy, balanced diet without increasing your portion sizes. Do not snack on foods that contain a lot of calories, such as crisps, cakes, biscuits and sweets. If you feel hungry between meals, eat fruit and vegetables and low-calorie foods.
Increasing your level of exercise will also help to keep your weight stable.
Memory problems
If you're having problems with your memory, speak to your doctor. They may want you to try a different medicine.
Headaches
Make sure you rest and drink plenty of fluids. It's best not to drink too much alcohol. Ask your pharmacist to recommend a painkiller. Headaches should usually go away after the first week of taking gabapentin. Talk to your doctor if they last longer than a week or are severe.
Getting more infections than usual
If you notice this, speak to your doctor.
Keep taking the medicine, but talk to your doctor if this advice does not help and the side effects bother you or do not go away.
Serious side effects
Very few people taking gabapentin have serious problems.
Call a doctor or call 111 straight away if you have a serious side effect, including:
- thoughts of harming or killing yourself – a small number of people taking gabapentin have had suicidal thoughts, which can happen after only a week of treatment
- a high temperature, swollen glands that do not go away, your eyes or skin turn yellow (this may be less obvious on brown or black skin), unusual bruises or bleeding, severe tiredness or weakness, unexpected muscle pain or weakness, with or without a rash – these may be symptoms of a serious reaction
- long-lasting stomach pain, feeling sick or being sick – these may be warning signs of an inflamed pancreas
- muscle pain or weakness and you're having dialysis treatment because of kidney failure
- seeing things that are not there (hallucinations)
Serious allergic reaction
In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to gabapentin.
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
Some people can become addicted to gabapentin. If this happens, you'll have withdrawal symptoms after you stop taking the medicine.
When you stop taking gabapentin, you'll need to reduce your dose gradually to avoid withdrawal symptoms. Do not stop taking gabapentin without talking to your doctor.
Talk to your doctor if you're concerned about becoming physically dependent on gabapentin.
Other side effects
These are not all the side effects of gabapentin. For a full list, see the leaflet inside your medicines packet.
You can report any suspected side effect using the Yellow Card safety scheme.