Pregabalin: nerve pain, anxiety and epilepsy explained

The NHS lists three uses: epilepsy, anxiety and nerve pain, which can come from diabetes, shingles or an injury. In epilepsy it is thought to reduce abnormal electrical activity in the brain. In nerve pain it is thought to block pain by affecting pain messages travelling through the brain and down the spine, and in anxiety to stop the brain releasing chemicals that make you feel anxious.

It is only available on prescription as capsules, tablets (standard and slow-release) or a liquid. It takes at least a few weeks to work, so judging it in the first days is not meaningful.

Standard tablets and capsules come in strengths from 25mg to 300mg, slow-release tablets contain 82.5mg, 165mg or 330mg, and 2.5ml of the liquid usually equals one 50mg capsule. The doctor starts with a low dose and raises it every few days to reduce side effects; once a suitable dose is found it normally stays the same.

Take it with or without food, but in the same way each day, and space doses evenly. Swallow tablets and capsules whole with water or juice. If you forget a dose, take it when you remember unless the next dose is within 2 hours. Never double up. For epilepsy, missing doses could trigger a seizure.

The NHS lists headaches, feeling sleepy, tired or dizzy, difficulty sleeping, diarrhoea, mood changes, nausea or vomiting, swollen hands, arms, legs and feet, blurred vision, difficulty getting an erection, weight gain and memory problems as common effects. Most are mild and wear off. Call a doctor or 111 for severe dizziness or fainting, hallucinations, problems going to the toilet such as blood in the urine, needing to pee more often or constipation, or a faster or slower heartbeat.

Call 999 or go to A&E for thoughts of harming yourself or ending your life, which can sometimes happen after only a week of taking it, and for signs of anaphylaxis. If you take more than prescribed and feel sleepy, confused or agitated, have a seizure or pass out, go to A&E.

Tell your doctor if you have had an allergic reaction to it, have ever misused or been addicted to a medicine, are trying to get pregnant, pregnant or breastfeeding, are on a controlled sodium diet or your kidneys do not work well (some liquid brands contain sodium), or have breathing problems, heart disease or liver or kidney disease.

Pregnancy: some but not all studies show a slight increase in birth defects, so it is usually only advised if the benefits outweigh the risks. Do not stop it without talking to your doctor, effective contraception is recommended, high-dose folic acid (5mg a day) is advised if planning or in pregnancy, and the baby may need extra monitoring at birth. Breastfeeding is usually possible if the baby is healthy, after talking to your doctor, because it passes into milk in small amounts.

It is usually safe with other medicines. The NHS asks you to tell the doctor before you start if you take strong opioids such as morphine, codeine or oxycodone, or anything that makes you sleepy or dizzy, because pregabalin can make those effects worse. Opioids at the same time can also make breathing difficult.

It is best to avoid alcohol, because it may make you sleepy, reduce focus and affect breathing. Pregabalin can intensify the highs of recreational drugs such as heroin and other opioids and increase unpleasant effects like panic attacks, anxiety and memory loss.

Some people can become addicted. Signs include finding it hard to stop or feeling the need to take it more than necessary. Do not stop suddenly even if you feel better: in epilepsy this can cause seizures that will not stop, and for any reason it can cause severe withdrawal such as anxiety, poor sleep, nausea, pain and sweating. Doctors reduce the dose gradually.

If you need to change to gabapentin, which works in a similar way but in different doses, the doctor explains how to switch safely.