Promethazine (Phenergan) can be suitable for some adults and children aged 6 years and above when used as directed and for no longer than 7 days without medical advice. However, it is not suitable for everyone. If you are considering promethazine hydrochloride for allergies, nausea, travel sickness, or short term insomnia, it is important to check whether you have a medical condition, take other medicines, or have another factor that could make promethazine unsuitable or require extra care.
This guide explains who should not take promethazine and who may need additional advice before using it. It covers important contraindications, cautions for conditions such as epilepsy and asthma, possible medicine interactions, pregnancy and breastfeeding, its legal classification in the UK, and the risks of incorrect or prolonged use. This information is based on the UK product information for Phenergan tablets and elixir.
Key things to know
- Absolute contraindications include known hypersensitivity to promethazine or other phenothiazines, coma or central nervous system depression, use of MAOIs within the previous 14 days, and children under 6 years of age. Promethazine should not be used in children under 6 because of the risk of serious respiratory and central nervous system effects.
- Extra caution may be needed if you have epilepsy, asthma, bronchitis, bronchiectasis, certain heart conditions, liver or kidney problems, glaucoma, or other conditions listed in the UK product information. These conditions do not all mean that promethazine is automatically unsuitable, but you should check with a doctor or pharmacist before using it.
- Promethazine is a pharmacy (P) medicine in the UK rather than a prescription only or controlled drug, for products such as Phenergan tablets and elixir.
- Promethazine is not generally recommended during pregnancy and should not be taken while breastfeeding. Alcohol should also be avoided while taking it because it can increase its sedative effects.
Promethazine is a first generation antihistamine that blocks histamine H1 receptors. This helps explain its use for allergic conditions such as hay fever and allergic rhinitis. It also has sedative and anticholinergic effects, which are why it may be used for short term insomnia in adults and travel sickness.
Common side effects can include drowsiness, dry mouth, and dizziness. Because promethazine can also affect the central nervous system and has anticholinergic effects, it can interact with other medicines and may not be suitable for some people. This is why checking your medical history and current medicines before use is important.
Who Should Not Take Promethazine at All
Certain situations are listed as contraindications in the UK product information. This means promethazine should not be used in these circumstances:
- A known allergy or hypersensitivity to promethazine, other phenothiazines, or any ingredient in the product. Allergic reactions can include rash, swelling, or difficulty breathing.
- Coma or central nervous system depression from any cause.
- Children under 6 years of age. Phenergan tablets and elixir should not be used in this age group because of the potential for serious respiratory and central nervous system effects.
- Anyone taking an MAOI, or who has stopped taking one within the previous 14 days. MAOIs are a type of medicine used to treat some mental health conditions. If you are unsure whether a medicine you take is an MAOI, ask a doctor or pharmacist before using promethazine.
These points come directly from the UK product information for Phenergan tablets and elixir. If you are unsure whether any of them apply to you, speak to a doctor or pharmacist before taking promethazine.
Conditions That Need Caution, Not Automatic Exclusion
Some medical conditions do not automatically mean that you cannot take promethazine, but they may require extra care and an appropriate clinical assessment before use:
- Epilepsy or a history of seizures. Phenothiazines, including promethazine, may lower the seizure threshold. The UK product information recommends caution and close monitoring in people with epilepsy.
- Asthma, bronchitis, bronchiectasis, and some other respiratory conditions. Promethazine can make bronchial secretions thicker and may make it harder to clear them by coughing. This may be particularly important for people with existing breathing problems.
- Liver or kidney problems, which may require additional consideration before treatment.
- Parkinson's disease, where some movement related side effects may be more difficult to manage.
- An underactive thyroid (hypothyroidism).
- Heart failure.
- A rare adrenal gland tumour called phaeochromocytoma.
- Myasthenia gravis.
- An enlarged prostate.
- Narrow angle glaucoma or a history of agranulocytosis, a serious reduction in certain white blood cells.
Older adults may be more sensitive to the anticholinergic and sedative effects of promethazine. This can increase the risk of confusion and other side effects, so additional caution may be appropriate. If you have any of these conditions, tell your pharmacist or prescriber during your consultation. They can consider your individual circumstances rather than assuming that promethazine is either automatically unsuitable or completely safe.
Promethazine and Epilepsy: What This Actually Means
If you have epilepsy or a history of seizures, promethazine is not necessarily ruled out, but you should have an appropriate assessment before taking it. Phenothiazines, the medicine group that includes promethazine, can lower the seizure threshold. The UK product information advises caution and close monitoring in people with epilepsy.
If you take anticonvulsant medicines, your pharmacist or prescriber can also check your current treatment and consider whether there could be any relevant interactions. Do not change your epilepsy medication or try to manage potential interactions yourself. If you are unsure whether promethazine is suitable for you, discuss it during your consultation.
Promethazine and Asthma
Promethazine can thicken or dry secretions in the airways and may make them more difficult to clear. This is why asthma, bronchitis, and bronchiectasis are listed as conditions where caution is needed in the UK product information.
This does not mean that everyone with asthma cannot take promethazine. However, if you have asthma or another respiratory condition, particularly if it is poorly controlled or you are currently unwell, speak to a pharmacist or prescriber before taking it.
If you develop serious breathing problems, including unusually slow or shallow breathing, seek urgent medical attention.
Can Diabetics Take Promethazine?
Diabetes is not listed as a specific contraindication or precaution for standard promethazine tablets or elixir in the UK product information. However, the injectable form of promethazine used in hospital settings has different safety information and may affect glucose tolerance. This information does not apply directly to the tablet or liquid formulations available through community pharmacies.
If you have diabetes and are considering promethazine, mention it during your consultation. Your pharmacist or prescriber can consider your overall health, other medicines, and the reason you want to take promethazine before advising whether it is appropriate for you.
Is Promethazine a Controlled Drug?
No. In the UK, promethazine tablets and elixir are classified as Pharmacy (P) medicines. This means they can be supplied by a registered pharmacy following an appropriate pharmacist assessment, without a prescription. Promethazine is not a controlled drug under the Misuse of Drugs Act.
The injectable form of promethazine has different legal and clinical requirements and is a prescription only medicine (POM). It is mainly used in clinical settings, which is different from the tablets and elixir commonly supplied through community pharmacies.
For official UK guidance on who can and cannot take promethazine, see the NHS page on who can and cannot take promethazine.
A Note on Misuse
Promethazine is intended for medical use and should be taken only as directed. Using more than the recommended amount, taking it for a purpose it was not intended for, or combining it with other sedating substances can increase the risk of harmful effects, including excessive drowsiness and breathing difficulties.
Alcohol can increase the sedative effects of promethazine. Combining promethazine with other central nervous system (CNS) depressants may also increase sedation and the risk of breathing problems. Higher doses can further affect alertness and coordination, which can make activities such as driving or operating machinery unsafe.
If you are concerned about your own use of promethazine or someone else's use, speak to a pharmacist or GP for appropriate advice.
Heart Rhythm: A Specific Caution Worth Understanding
Promethazine and other phenothiazine medicines can affect the heart's electrical activity and may prolong the QT interval. In rare cases, this can contribute to a serious abnormal heart rhythm.
The risk may be higher if you take other medicines that can also affect the QT interval, have a slow heart rate, or have low levels of potassium or other electrolytes. Certain antiarrhythmics, antibiotics, antidepressants, and antipsychotics can also affect heart rhythm.
This is one reason it is important to provide your pharmacist or prescriber with a complete list of medicines you take. They can check for relevant interactions and consider whether promethazine is appropriate for you.
Drug Interactions Worth Knowing About
Important drug interactions and precautions include:
- MAOIs: Promethazine should not be used with MAOIs or within 14 days of stopping an MAOI because of the potential for serious interactions.
- Other sedating antihistamines: Do not combine promethazine with another sedating antihistamine, such as chlorphenamine or diphenhydramine, unless a healthcare professional has specifically advised you to do so.
- Alcohol: Avoid alcohol while taking promethazine because it can increase drowsiness and other sedative effects. Combining it with other CNS depressants may also increase the risk of breathing difficulties.
- Medicines that can lower the seizure threshold: Combining these with promethazine may require careful clinical consideration, particularly if you have epilepsy or a history of seizures.
- Other medicines, supplements and herbal products: Tell your pharmacist or prescriber about everything you take, including non prescription medicines, supplements, and herbal products. This helps them check for possible interactions and other safety concerns.
- Antacids containing aluminium, magnesium, or calcium: These may affect the absorption of some medicines. If you take an antacid, ask your pharmacist whether you need to leave a gap between it and promethazine.
- Medicines that prolong the QT interval: Some antiarrhythmics, antibiotics, antidepressants, and antipsychotics can affect the QT interval. Taking them with promethazine may increase the risk of heart rhythm problems and should be checked by a healthcare professional.
Non sedating antihistamines, such as fexofenadine (Telfast), do not have the same sedating effects as promethazine. However, taking two antihistamines together is not generally recommended unless a healthcare professional has advised you to do so. If you already take a non sedating antihistamine and are considering promethazine, mention this during your consultation rather than combining them without checking first.
If you do start promethazine, our Phenergan side effects guide explains the possible side effects in more detail, including when drowsiness the following day may be worth discussing with a pharmacist.
Pregnancy and Breastfeeding
Promethazine is not generally recommended during pregnancy or breastfeeding unless a healthcare professional advises otherwise. If you're pregnant, trying to conceive, or breastfeeding and are considering promethazine for any reason, discuss this with your GP or midwife rather than taking it based on general guidance, since alternatives with a better-established safety profile in these situations are usually preferred.
Children and Promethazine
Promethazine should not be used in children under 6 years of age, and children under 2 years of age are the group most associated with fatal respiratory depression warnings. For children aged 6 to 9 years, lower doses than those used in adults may be appropriate, depending on the indication and product formulation, and should be confirmed with a doctor or pharmacist rather than assumed, as body weight may also matter depending on the product guidance and indication. From age 10, dosing generally follows the same pattern as adults, depending on what's being treated. None of this is a substitute for checking the specific product's patient information leaflet or asking a pharmacist directly, since promethazine is available in different strengths and formulations, and the correct dose depends on both age and what's actually being treated, whether that's an allergy, nausea, or occasional sleep difficulty. Some children can also have psychomotor hyperactivity or other paradoxical excitation instead of becoming sleepy.
If you're unsure whether promethazine is suitable for you, speak to a pharmacist or prescriber before starting treatment, rather than leaving you to guess based on a general guide alone.
Sources
- NHS: Who can and cannot take promethazine (nhs.uk/medicines/promethazine/who-can-and-cannot-take-promethazine)
- NHS: About promethazine (nhs.uk/medicines/promethazine/about-promethazine)
- Electronic Medicines Compendium (emc): Phenergan 25mg tablets and Phenergan Elixir Summary of Product Characteristics (medicines.org.uk)
Medical Disclaimer
This page provides general information about who can and cannot take promethazine, based on UK product information. It is not a substitute for personalised medical advice, diagnosis, or treatment.
Whether promethazine is suitable for you depends on your individual health, other medicines you take, and your circumstances. A pharmacist, prescriber, or GP can assess whether it is appropriate for you.
The contraindications and cautions described here are based on the licensed UK tablets and elixir. Other promethazine formulations or products available in other countries may have different information.
If you are unsure whether promethazine is suitable for you, speak to your pharmacist, prescriber, or GP before taking it.
