Promethazine

What is promethazine?

Promethazine, also known by brand names like Phenergan, Sominex (used primarily for sleep in the UK) and others, is a drowsy or sedating antihistamine used to treat a variety of conditions. These are typically conditions related to allergies, nausea and sleep problems, with promethazine calming and relieving their symptoms[1].

What is promethazine used for?

Promethazine is used to treat many different conditions. These include, but may not be limited to, allergic conditions such as hay fever,  urticaria (hives)  and allergic rhinitis. It can also be used to ease symptoms of motion sickness, vertigo, general nausea, vomiting, and short-term sleep problems such as insomnia[1].

How does promethazine work?

Promethazine blocks the effects of histamine – a substance in the body that causes allergic symptoms. It also affects other natural chemicals, such as acetylcholine, and has a calming effect on the brain.

Specifically, it works by blocking histamine H1 receptors, which reduces allergy symptoms. It also acts on the brain to help reduce nausea, while also producing anticholinergic and sedative effects that can help with sleep difficulties and motion sickness[1].

Who can take promethazine?

Most adults and children over the age of two can take promethazine. However, some forms are only suitable for children aged five or older.

It may also not be suitable for those with certain conditions. You should speak to a doctor or pharmacist before taking promethazine if you have asthma, epilepsy, glaucoma, prostate problems or liver disease. It may also not be suitable for those that are elderly, as it may increase the risk of confusion or falls, or those that are pregnant or breastfeeding[1].

Please tell your doctor or pharmacist about any conditions you may have before you start treatment and always follow the instructions in the Patient Information Leaflet[2].

How do you take promethazine?

Promethazine is available as 10mg, 20mg, or 25 mg tablets or 5mg (in 5ml) liquid. It may also be administered as an injection in hospital settings.

When taking tablets or liquid, you can take it with or without food. If you’re taking promethazine for motion sickness, you’ll generally take it in the hours before travel for maximum effect. For sleep problems, you can take it shortly before going to bed.

Always follow the instructions provided in the Patient Information Leaflet or by your doctor or pharmacist[1].

What is the typical dosage of promethazine?

A usual promethazine dosage depends on what the medicine is being used to treat[1]:

• For allergies, a typical dose is 10 to 20mg two or three times a day, or 25 mg once or twice a day

• For motion sickness, 25mg the night before your journey is the usual dose, or 25mg at the onset of symptoms followed by another 25mg later on that evening

• For sleep problems, 20mg to 50mg at bedtime is the usual dose

• For vertigo, the dose can vary from 25mg a day to 25mg 4 times a day as prescribed

Children and some adults may have a lower dose. You should always follow the dose recommended by your doctor, pharmacist or as listed on the packaging.

Can you stop taking promethazine suddenly?

Yes, you can usually stop taking promethazine when you no longer need it if it’s being used for short-term treatment. If you have been taking it regularly for a long time, speak to your doctor or pharmacist before stopping to ensure you do so safely[1].

What should you do if you take too much promethazine?

Taking too much promethazine can be dangerous. The signs and symptoms of taking too much may include severe drowsiness and confusion. Seizures, breathing difficulties, and a fast or irregular heartbeat are rarer but more serious side effects. You should call 999 or go to A&E immediately if you think you or someone else has taken too much promethazine[1].

What should you do if you forget a dose of promethazine?

If you are using promethazine occasionally – for example, for travel or sleep – you can skip the missed dose and continue from the next one. If you are using it regularly for allergies or similar, take the missed dose as soon as you remember, unless it is nearly time for your next dose. Never take a double dose to make up for a missed one[1].

What medicines should you avoid while taking promethazine?

Promethazine can interact with some other medicines. As such, you should avoid taking promethazine with[1]:

• Other prescribed sedatives or sleeping tablets

• Over-the-counter medicines (e.g., cough syrups with sedatives) as they could also contain promethazine

• Antidepressants, especially tricyclics or MAOIs

• Opioid painkillers

It’s also best to avoid alcohol, as it can increase drowsiness and side effects. Always check with your doctor or pharmacist before combining promethazine with any other medicines. This includes over-the-counter medicines or herbal remedies[1].

Always inform your doctor or pharmacist about all medications and supplements you take before you start a new medicine, and follow the instructions in the Patient Information Leaflet[2].

What are the side effects of promethazine?

The most common side effects when taking promethazine are daytime tiredness, nightmares, dizziness or an unsteadiness on your feet, concentration problems, and headaches. More serious side effects, for which you should seek medical help immediately, include confusion, blurred vision, difficulty peeing, breathing difficulties, seizures, yellowing of eyes or skin, or severe allergic reactions such as rashes or swelling.

If you experience any side effects, including those not listed, you are encouraged to report them via the Yellow Card Scheme or contact your doctor, pharmacist, or nurse. This information is intended as a summary for general awareness and does not replace professional medical advice.

The information provided in the side effects section is not a comprehensive list of all possible side effects associated with this medication. For a complete list of side effects, please refer to the Patient Information Leaflet (PIL) provided with your medication or consult your healthcare professional[2].

Frequently asked questions about promethazine

Can I drive or operate machinery while taking promethazine?

You should not drive or use machines until you know how promethazine affects you. That is because it can cause drowsiness and slow your reaction, endangering you and others[1].

Is promethazine addictive?

Promethazine is not typically addictive. However, misusing it, especially when combined with opioids, can be dangerous and lead to serious side effects[1].

Can I drink alcohol while taking promethazine?

No, it’s best to avoid alcohol when you take promethazine. Alcohol can increase the sedative effects and raise the risk of side effects[1].

Can I take promethazine long-term?

Long-term use of promethazine is usually not recommended. That’s particularly true in older adults, as it may increase the risk of side effects such as confusion or memory problems[1].

For the official NHS guide to promethazine, visit their website.