Updated over a week ago

Promethazine is used to treat adults with difficulty sleeping (insomnia).

We'd like to give you some important information before you start taking it. It is also recommended to read the patient information leaflet to understand how the medication works, what to expect, and potential side effects and how to manage them

Do understand how it works

Promethazine is what is known as a drowsy antihistamine. Yes, that’s the type of drug most commonly associated with the treatment of allergies. But this particular type of antihistamine has been found to encourage feelings of drowsiness and promote the onset of sleep for short term treatment.

While most often associated with allergies such as hay fever, histamine plays an important role in the sleep-wake cycle too. Specifically, studies show histamine to be responsible for a state of vigilance and alertness when you are awake.

What promethazine does is block the chemical histamine. That means that any feelings of alertness fade and you become more relaxed. This way, sleep comes much more easily.

For people with insomnia, promethazine is highly effective. Studies have shown that promethazine can increase sleep time, reduce night-time awakenings, and improve perceived sleep quality.

Don’t take if you:

  • You are taking a medicine for depression called a monoamine oxidase inhibitor (MAOI). Also do not take Promethazine if you have stopped taking one of these MAOI medicines within the last 14 days.

  • Have ever had an allergic reaction to promethazine

  • Have an eye problem called primary angle closure glaucoma

  • Have problem peeing or emptying your bladder

  • Have epilepsy or any other health problem that causes seizures or fits

  • Are due to have an allergy test. Promethazine can affect the results so you may need to stop taking at least 3 days before your test.

  • Are trying to get pregnant. Promethazine can affect home pregnancy tests.

Promethazine may not be suitable if:

  • You have difficulty breathing, wheezing, tightness in the chest (asthma) or an infection in your lungs (bronchitis)

  • You have epilepsy

  • You have any serious heart problems

  • If you have any personal or family history of heart disease

  • If you have an irregular heartbeat

  • You have liver or kidney problems

  • You have a stomach blockage or difficulty passing water

  • You have hearing problems

  • You have increased pressure in the eye (narrow angle glaucoma)

  • You have had something called Reye’s Syndrome or possible Reye’s Syndrome – signs include being sick and confused following a viral illness

Do take correctly

  • Take one 25mg tablet when required, 30 minutes prior to sleep

  • Swallow the tablets whole. Don’t chew them, as this can affect the way the medicine is absorbed. The best way to take the tablets is with a glass of water, to ensure that you swallow them easily.

  • Don’t take more than the recommended dose, and don’t take two doses at the same time. This can increase your risk of side effects (more on these below).

  • Avoid alcohol when taking promethazine, as it increases the chance of side effects too.

All sleep medicines work best when combined with a healthy, active lifestyle that is conducive to sleep. Exercising regularly, cutting down on alcohol and caffeine, and creating an optimal environment for sleep will all help.

Do be aware of the possible side effects

If you experience any of the following serious (but uncommon) side effects, you should stop taking promethazine and seek urgent medical attention:

  • An allergic reaction. The signs may include: a rash, swallowing or breathing problems, swelling of your lips, face, throat or tongue

  • Liver problems that may cause the eyes or skin to go yellow (jaundice)

  • Muscle stiffness or shaking

  • Being unable to control some muscles in your head or face

  • You notice unusual movements of the tongue, facial muscle spasms, rolling eyes and trembling

  • Very fast, uneven or forceful heartbeat (palpitations)

  • Irregular heartbeat

  • Tiredness which lasts for a long time. This may be due to a blood problem called anaemia

Some of the most commonly reported side-effects of promethazine are:

If you experience any of the symptoms below that become serious or last longer than a few days stops taking promethazine and seek medical attention:

  • Dry mouth, blurred vision or you cannot pass water (urine)

  • Feeling drowsy or sleepy, tiredness, disorientation, having nightmares, headaches, feeling restless

  • Loss of appetite (anorexia), indigestion

  • Feeling dizzy, lightheaded, faint (hypotension)

  • Feeling confused, especially in elderly people

  • Being more sensitive to the sun than usual. If this happens keep out of direct sunlight and do not use sun lamps

  • Unpleasant sensation or an overwhelming urge to move the legs (also called Restless Legs Syndrome)

Additional cautions: Promethazine can make your skin more sensitive to sunlight. Keep out of direct sunlight while taking this medicine.

Pregnancy and breast-feeding

Talk to your doctor or pharmacist before taking this medicine if you are pregnant, might become pregnant, or think you may be pregnant. Promethazine Tablets should not be taken 2 weeks before birth.

You should not take promethazine tablets if you are breast-feeding. This is because small amounts may pass into mothers’ milk. This can be harmful to your baby.

If you have any questions about taking promethazine please get in touch by emailing [email protected] or if you feel unwell and feel you need urgent medical attention please call NHS 111 or attend your nearest accident and emergency department.

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