If you are using Phenergan (promethazine) to help with sleep, the usual adult dose is one 25mg tablet at bedtime. It is intended for short term use and should not be used for more than 7 days unless a doctor advises you to continue.
If you are looking for short term help with sleep problems, it is useful to know more than just the dose. You may also want to know how often you can take Phenergan, whether it can become less effective with regular use, what to expect when you stop, and when it is better to speak to a GP.
Phenergan is intended for short term use. If you continue to have problems sleeping, it is worth looking at what may be causing them rather than relying on a sedating antihistamine for longer than recommended. Below, we explain the usual dose, how often it can be taken, key safety points, and what to do if a week is not enough. For more information about the dose, see our companion dosage guide.
How Long Can You Take Phenergan (a Drowsy Antihistamine) for Sleep?
Phenergan for sleep is intended for short term treatment. You should not take it for more than 7 days without medical advice.
It may be useful for a short period when you are having trouble sleeping, but it is not intended as a long term treatment for ongoing insomnia. If you still need help sleeping after about a week, speak to your GP or pharmacist rather than continuing to take it on your own. They can help look at possible reasons for your sleep problems and suggest suitable next steps.
How Many Can You Take, and How Often?
For adults, the usual dose for sleep is one 25mg tablet at bedtime. This is the dose for the night.
Do not take another tablet later in the night just because the first one does not seem to have worked. Do not take more than the recommended dose. Taking more does not necessarily improve sleep and may increase the chance of side effects such as drowsiness or dizziness.
If one 25mg tablet does not seem to help, speak to a pharmacist or GP rather than increasing the dose yourself.
Why It May Stop Working If You Take It Every Night
One reason Phenergan is intended for short term use is that the sedating effect of antihistamines such as promethazine can become less noticeable with regular use in some people.
This means that taking it every night may not continue to have the same effect. It can also be tempting to take more when the usual dose does not seem to work, which can increase the risk of side effects.
If you find that you need Phenergan every night to sleep, speak to a GP or pharmacist rather than increasing the dose or continuing it for longer than recommended.
Can You Become Reliant on It?
Promethazine is not a controlled drug in the same way as some prescription sleeping medicines, such as benzodiazepines. However, taking a sleep aid regularly can become part of your bedtime routine, and you may start to feel that you cannot sleep without it.
If you find yourself relying on Phenergan every night or feeling worried about sleeping without it, speak to a GP or pharmacist. They can help you look at the cause of your sleep problems and whether you need a different approach.
What Happens When You Stop?
If you have only taken Phenergan for a short period, you can usually stop taking it when you no longer need it.
If you have been using it regularly for longer than recommended, your sleep may feel different when you stop. You may notice that your original sleep problems are still there, rather than this being a sign that you need to restart the medicine.
If you have been taking Phenergan regularly for longer than advised and are unsure how to stop, speak to a GP or pharmacist for advice.
How Long Does It Take to Work?
The time it takes for Phenergan to make you feel drowsy can vary between people. For this reason, do not use the clock to decide whether you need another tablet.
If you have taken the recommended dose and do not feel drowsy after a short time, do not take an extra tablet. Taking more than recommended can increase the risk of side effects.
Take Phenergan when you are ready to settle down for the night and allow enough time for its drowsy effects before you need to get up or do anything that requires you to be alert.
A Note on 50mg Promethazine Hydrochloride
You may see questions about taking 50mg of promethazine for sleep. With 25mg tablets, 50mg would mean taking two tablets, which is more than the usual adult dose for sleep.
Do not increase your dose to 50mg on your own. If one 25mg tablet is not helping, speak to a pharmacist or GP about what to do next. Do not take extra tablets simply because the first dose does not seem to be working.
The companion dosage guide covers Phenergan dosing in more detail.
When to See a GP
Speak to your GP or pharmacist if your sleep problems continue for more than a week, get worse, or keep coming back.
You should also ask for advice if you are taking other medicines that can make you drowsy, as combining medicines with sedating effects can increase drowsiness and other side effects.
Ongoing insomnia may have different possible causes, including stress, anxiety, changes to your routine, other health problems or medicines. A GP can help you look at possible causes and decide whether you need further assessment or treatment.
Good sleep habits can also help, such as keeping a regular sleep schedule, having a relaxing bedtime routine and limiting things that can interfere with sleep.
Safety Points and Side Effects
Phenergan can cause drowsiness, dizziness and other side effects. The effects can continue into the following morning in some people, so do not drive, cycle or operate machinery if you feel sleepy, dizzy or less alert.
Do not drink alcohol while taking Phenergan, as alcohol can add to its sedating effects.
Phenergan may not be suitable for everyone. Check with a doctor or pharmacist before taking it if you are older, pregnant, planning a pregnancy or breastfeeding, or if you have asthma or other breathing problems, glaucoma, an enlarged prostate, or liver or kidney problems.
Tell your doctor or pharmacist about any other medicines you take, particularly medicines that can cause drowsiness. Some medicines can interact with promethazine, including certain antidepressants.
Do not give Phenergan to children to make them sleep. Age restrictions can vary depending on the specific Phenergan product, so always check the product information and use the medicine only as directed.
If you have taken an MAOI antidepressant within the last 14 days, check with a doctor or pharmacist before taking promethazine.
For the full list of warnings and possible side effects, check the patient information leaflet supplied with your medicine.
