Gabapentin: nerve pain, epilepsy and why stopping must be gradual

The NHS says gabapentin is used to treat epilepsy and is also taken for nerve pain, which can be caused by different conditions such as diabetes and shingles or by an injury. In epilepsy it is thought to reduce abnormal electrical activity in the brain. In nerve pain it is thought to affect the pain messages travelling through the brain and down the spine.

It is a prescription medicine supplied as capsules, tablets or a liquid. Most people do not need to stay on one brand, since there is very little difference between brands, although a doctor may recommend continuity for someone whose epilepsy has been hard to control.

The NHS lists capsule strengths of 100mg, 300mg and 400mg and tablet strengths of 600mg and 800mg, with a liquid that usually contains 50mg in 1ml. For epilepsy in adults and children aged 12 and over, and for nerve pain in adults, it gives the usual range as 900mg to 3,600mg a day, split into 3 doses. The prescriber starts low and increases over a few days, and the dose usually stays the same once it suits you.

Swallow capsules and tablets whole with water or juice and do not chew them. Use the syringe or spoon with a liquid, not a kitchen spoon. If you forget a dose, take it when you remember unless the next is due within 2 hours; never double up. In epilepsy, missed doses may trigger a seizure.

Most people do not get side effects, and common ones are usually mild and go away by themselves. They include sleepiness, tiredness and dizziness, nausea, vomiting, diarrhoea, mood changes, swollen arms and legs, blurred vision, dry mouth, difficulty getting an erection, weight gain, memory problems, headaches and getting more infections than usual. If drowsiness or dizziness has not eased within a week or two, a doctor may lower the dose or increase it more slowly.

Call a doctor or 111 for a high temperature with swollen glands, yellow skin or eyes, unusual bruising or bleeding, severe tiredness or unexpected muscle pain; long-lasting stomach pain with sickness (possible pancreatitis); hallucinations; or trouble breathing. Call 999 or go to A&E if you have thoughts of harming yourself or ending your life, or signs of anaphylaxis.

Some people can become addicted to gabapentin, and signs include finding it hard to stop or feeling a need to take it more often than necessary. Because it is a controlled medicine, pharmacists ask for proof of identity, you sign the back of the prescription, a prescription may need hand-signing by a doctor, and it must be collected within 28 days or it becomes invalid. Requesting repeats up to 5 days early is advised.

Never stop gabapentin suddenly, even if you feel better. In epilepsy this can cause seizures that will not stop. For any reason, suddenly stopping can cause severe withdrawal such as anxiety, difficulty sleeping, feeling sick, pain and sweating. Gradual dose reduction prevents this, so speak to your doctor first.

Gabapentin is not generally recommended in pregnancy because there is not enough information about safety, although from the small amount available there is no clear evidence it is harmful. It should only be taken if the benefit outweighs the risk. If you take it for epilepsy, keep taking it and speak to your doctor urgently, because seizures can harm you and the baby. High-dose folic acid (5mg a day) is recommended if trying to conceive or pregnant. A baby may need extra monitoring after birth because of possible withdrawal.

If your baby is healthy you can take it while breastfeeding after talking to your doctor or pharmacist; it passes into milk in very small amounts, and bed-sharing should be avoided. Tell the prescriber if you have misused or been addicted to a medicine, have kidney problems or a controlled sodium or potassium diet (the liquid contains both), or have a lung condition such as COPD or severe asthma.

Strong painkillers such as morphine can make you very tired and dizzy when you start gabapentin. Check with a pharmacist if you take antidepressants such as amitriptyline or fluoxetine, or antipsychotics such as olanzapine. Herbal products that make you dizzy or drowsy could add to those effects. It can intensify the highs of recreational drugs like heroin and other opioids and raise the chance of panic attacks, anxiety and memory loss.

You can drink alcohol, but it may make you sleepy; it may be best to avoid it in the first few days. You may feel sleepy, tired or dizzy when you start or when the dose rises, so do not drive, cycle or use machinery until you feel better. People with epilepsy are generally not allowed to drive until seizure-free for 1 year, or having only had seizures in sleep, and should ask their doctor about driving if the medicine changes.