Prochlorperazine (Stemetil, Buccastem): uses and cautions

Prochlorperazine is an anti-emetic, meaning it stops you feeling or being sick. The NHS lists sickness in pregnancy, dizziness or a spinning sensation, motion sickness, nausea due to migraines, sickness after general anaesthetic, sickness caused by cancer treatment or other medicines and balance problems such as Ménière's disease. It is occasionally used for anxiety. It is also available as an injection, generally given in hospital.

It belongs to the phenothiazine group, which is thought to block the chemical dopamine in the brain. That stops nausea signals reaching the vomiting centre, the area that controls when you feel sick or vomit. Other anti-sickness medicines named by the NHS include metoclopramide, ondansetron, domperidone and cyclizine, which suit different types of sickness. It is usually best to take only one type of anti-sickness medicine at a time.

The dose depends on the reason, but you usually take it 2 to 3 times a day, and doses for children aged 1 to 17 are based on weight. Standard tablets are swallowed whole with water, with or without food. Buccal tablets dissolve between the upper lip and the gum and work best after meals, giving them longer to dissolve; taking them after food also prevents swallowing them before they dissolve.

It should be used for the shortest time and at the lowest dose that works. It can be taken long term if your doctor advises it, but stopping suddenly after a long time can cause withdrawal symptoms such as feeling or being sick and sleep problems, so talk to your doctor, who will probably reduce the dose gradually. It is not usually addictive.

For motion sickness, take a missed dose as soon as you remember; for any other use, skip it and take the next at the usual time. Never take two doses together. Taking too much can be dangerous: contact 111 if you take more than recommended, and do not drive to A&E.

Side effects are usually mild and pass by themselves: feeling sleepy or drowsy, blurred vision, dry mouth, headache and a stuffy nose. Avoid driving, cycling or tools while sleepy or with blurred vision, and speak to a doctor if blurred vision lasts more than a day or two. Sugar-free gum may help a dry mouth.

Serious effects are rare, in fewer than 1 in 10,000 people. Call a doctor or 111 straight away for muscle stiffness or shaking or uncontrollable face or tongue movements, a sudden high temperature or infection, sore breasts in men or women, yellowing of the eyes or skin, or a fast, irregular or pounding heartbeat. Swelling of the lips, mouth, throat or tongue needs 999. Suspected side effects can be reported through the Yellow Card scheme.

Most adults and children aged 1 and over can take prochlorperazine. Tell a doctor or pharmacist if you have ever reacted to it or another medicine, or have phaeochromocytoma, glaucoma, a history of or higher risk of blood clots, a condition that can block the bowel such as Crohn's disease, diverticulitis, a hernia or colon cancer, liver problems, epilepsy or fits, high blood pressure, heart failure, an enlarged prostate or a condition that affects your blood.

Tell your pharmacist or doctor about any medicine that makes you sleepy, gives you a dry mouth or can affect your heart, because prochlorperazine may worsen those effects. Some herbal remedies can worsen side effects too. The NHS says it is best not to drink alcohol, which can add to sleepiness or an irregular heartbeat, and that you can otherwise eat and drink normally. It does not affect contraception, but vomiting can reduce the pill's protection, so check the pill packet.

Prochlorperazine can be taken in pregnancy and there is no evidence that it harms the baby, though there are several treatments for pregnancy sickness and a doctor or pharmacist can advise which is best. If your baby is healthy you can usually take it while breastfeeding, but it is better only occasionally or for a short time; tell a professional if your baby is unusually sleepy, irritable or feeding poorly.

It can raise the hormone prolactin, which if too high may stop periods in women and cause erectile dysfunction in men, though this is not usually an issue with short use for sickness.