This page answers common questions about promethazine (Phenergan), including the maximum dose, whether 100mg is safe, and what to do if you have taken too much. For adults using promethazine for allergy symptoms, the usual dose stated in the product information is 25mg up to three times a day, giving a total of 75mg in 24 hours. For sleep, the usual dose is one 25mg tablet at bedtime.
Do not take more than the recommended dose unless a doctor has specifically told you to do so. The right dose can depend on why you are taking promethazine, your age, other medicines you use and your health.
You will also find information about possible signs of an overdose, what to do if too much has been taken, why there is no specific antidote, how to avoid taking an extra dose by mistake, and when you may need extra advice. Taking more than recommended can increase the risk of serious side effects, so it is important to get medical advice if you think you have taken too much.
The Maximum Dose of Promethazine
For adults using promethazine for allergy symptoms, the patient information leaflet gives a dose of 25mg up to three times a day. This gives a total of 75mg in 24 hours.
For sleep, the usual dose is one 25mg tablet at bedtime. Do not take additional tablets during the night because you do not feel that the first dose has worked.
The correct dose can vary depending on the reason for treatment and the particular promethazine product. Do not increase the dose yourself if you feel that it is not working. Speak to a pharmacist or doctor instead.
You may see other sources mention higher daily doses, but this does not mean that a higher dose is suitable for self care. Always follow the dose on your medicine packaging or the instructions given by your prescriber.
Is 100mg of Promethazine Safe?
You should not take 100mg of promethazine on your own. This is above the 75mg total daily dose stated in the patient information for the usual adult allergy dose.
A doctor may use different doses in specific clinical situations, depending on the person's condition and other factors. This does not mean that you should take a higher dose without medical advice.
Taking more promethazine than recommended can increase the risk of side effects, including marked drowsiness, dizziness and confusion. In more serious cases, problems with breathing or heart rhythm can occur.
If you have taken around 100mg or more than your prescribed dose, do not take any more. Seek medical advice promptly, even if you currently feel well.
What to Do If You Take Too Much
If you think you have taken more promethazine than recommended, get medical advice rather than trying to manage it yourself.
- If someone is very drowsy and difficult to wake, confused or severely agitated, having a seizure, having difficulty breathing, or has collapsed, call 999 or go to A&E immediately.
- If too much has been taken but the person is awake and does not have severe symptoms, contact NHS 111 or speak to a pharmacist for advice as soon as possible.
- Have the medicine packaging with you or nearby. It can help the healthcare professional identify the medicine, strength and amount taken.
- Tell the healthcare professional about any other medicines, alcohol or substances that were taken at the same time.
Do not make yourself vomit or try to treat an overdose at home. If you are unsure how much was taken, it is still important to seek advice.
In hospital, healthcare professionals may monitor things such as breathing, heart rate, blood pressure and level of consciousness. Treatment depends on the amount taken and the symptoms.
Is There an Antidote for Promethazine?
There is no specific antidote for promethazine.
If too much has been taken, treatment focuses on monitoring and supporting the person's vital functions while the medicine leaves the body. This may include monitoring breathing, blood pressure, heart rhythm and level of consciousness.
If someone has severe symptoms such as difficulty breathing, a seizure or a reduced level of consciousness, they may need urgent treatment in hospital.
This is why you should not try to treat a suspected overdose with another medicine or a home remedy.
Avoiding an Accidental Overdose
A few simple habits can help reduce the chance of taking too much promethazine:
- Follow the dose on the packaging or the instructions given by your doctor.
- Do not take an extra dose because the first dose does not seem to have worked.
- Check the active ingredients in cough, cold and sleep products before taking them alongside promethazine. Some combination medicines may contain ingredients that can cause drowsiness.
- Do not combine promethazine with other sedating medicines unless a doctor or pharmacist has advised you to do so.
- Avoid alcohol while taking promethazine because it can increase drowsiness and other sedating effects.
- Keep promethazine in its original packaging so you can easily check the strength and dose.
- Keep it out of the sight and reach of children.
If you take several medicines, a pharmacist can check them for you and help you avoid taking the same or similar ingredients more than once.
Who Should Not Take Promethazine for Motion Sickness
Promethazine is a sedating first generation antihistamine. It may not be suitable for everyone.
Do not give promethazine to children under the age stated on the product packaging. Promethazine should not be used to make a child sleep, and there are important warnings about its use in very young children.
Do not take promethazine if you have had an allergic reaction to promethazine or other phenothiazines. You should also check with a doctor or pharmacist if you have taken an MAOI antidepressant within the last 14 days.
Ask a doctor or pharmacist for advice before taking promethazine if you are older, as you may be more sensitive to some side effects, or if you have asthma or other breathing problems, glaucoma, an enlarged prostate, epilepsy or another seizure disorder, liver or kidney problems, difficulty passing urine, or a condition that causes a very dry mouth.
Promethazine can add to the sedating effects of alcohol, opioid painkillers, benzodiazepines and other medicines that cause drowsiness. Tell your doctor or pharmacist about all the medicines you take before using it.
If You Are Struggling
If you have taken too much promethazine deliberately or are having thoughts of harming yourself, please treat this as an emergency. Call 999 or go to A&E if you are in immediate danger or have taken an overdose.
You can also call Samaritans on 116 123, free of charge, if you need someone to talk to. For urgent health advice, you can contact NHS 111.
You do not have to deal with this on your own. Reaching out to a healthcare professional, a trusted person or a support service can help.
