If you are pregnant, planning a pregnancy, or searching for information about Phenergan during pregnancy in the UK, you may have come across advice that appears to conflict. The leaflet supplied with Phenergan says that use during pregnancy is not recommended unless the potential benefits outweigh the potential risks. NHS guidance, however, states that promethazine can be taken during pregnancy and that there is no evidence that it harms the baby. These statements come from different types of guidance and should be considered in context.
The manufacturer's advice is deliberately cautious and reflects the wording used in the product information. NHS and specialist UK guidance considers the available evidence and how promethazine may be used in clinical practice. This is why it is important to discuss the medicine with your midwife, GP or pharmacist before taking it during pregnancy.
This guide explains the UK position using information from the NHS, the National Institute for Health and Care Excellence, the UK Teratology Information Service and the manufacturer's product information. It looks at how promethazine may be used for pregnancy sickness, what is known about its use during pregnancy, and what to discuss with your healthcare professional before taking it.
Key things to know about side effects
- NHS guidance states that promethazine can be taken during pregnancy and that there is no evidence that it harms the baby. However, you should still discuss its use with a healthcare professional.
- NICE Clinical Knowledge Summaries list promethazine as one of the antiemetics that may be considered for nausea and vomiting in pregnancy, alongside medicines such as cyclizine.
- The UK Teratology Information Service, through its BUMPS information, describes promethazine as an option that may be used for pregnancy sickness. Available information has not identified concerns about an increased risk of birth defects.
- The manufacturer's Summary of Product Characteristics takes a more cautious approach and states that use during pregnancy is not recommended unless the potential benefits outweigh the potential risks. This wording reflects the product licensing information and does not, by itself, mean that promethazine has been shown to cause harm during pregnancy.
- The UK does not use the American A to X pregnancy category system for medicines. These categories were used in the United States and have since been removed from US medicine labelling.
- Pregnancy sickness can range from mild nausea to severe vomiting that may require medical treatment. If you are struggling to keep food or fluids down, speak to your midwife, GP or another healthcare professional rather than trying to manage the symptoms on your own.
- If you are considering an over the counter medicine during pregnancy, ask a pharmacist whether it is suitable for you. Your individual circumstances, other medicines and stage of pregnancy may all be relevant.
The short answer
Promethazine is one of the medicines that UK healthcare professionals may consider when a pregnant woman needs treatment for nausea and vomiting. It has been used during pregnancy for many years, and available evidence has not identified a major increase in the risk of birth defects. However, this does not mean that every pregnant person should take it or that it is suitable in every situation.
What the guidance does not mean is that you should decide to take promethazine without advice. Nausea and vomiting during pregnancy can vary considerably in severity, and more severe symptoms may need assessment and treatment. Your healthcare professional can help determine whether medication is appropriate and which option may be most suitable for you.
That is the main distinction this guide focuses on: promethazine may be an option during pregnancy, but whether you should take it is an individual healthcare decision.
Why the packet and the NHS seem to disagree
This is the single biggest source of confusion, and most online articles never address it. The two documents are answering different questions.
| Source | What it says | What it is actually telling you |
|---|---|---|
| Summary of Product Characteristics (Phenergan, revised June 2024) | Use is not recommended during pregnancy, and in women of childbearing potential not using contraception, unless the potential benefits outweigh the potential risks | This is the marketing authorisation wording. Promethazine was licensed long before modern pregnancy studies existed, and there are no animal reproductive toxicity studies on file, so the licence stays conservative |
| NHS medicines guidance (reviewed May 2025) | Promethazine can be taken in pregnancy, and there is no evidence that it is harmful to your baby | This reflects decades of real world use and the evidence that has accumulated since the licence was written |
| NICE Clinical Knowledge Summaries | Promethazine or cyclizine are recommended first line for nausea and vomiting in pregnancy | This is what a GP is likely to follow when treating pregnancy sickness |
| UKTIS, via the bumps patient leaflets (June 2025) | Promethazine can be used during pregnancy and is a recommended treatment for pregnancy sickness | This is the UK's specialist teratology service, which exists specifically to answer this question |
Conservative licensing wording should not automatically be interpreted as evidence of harm . When national guidance and specialist teratology advice are considered together, they provide the basis for current UK clinical practice . The leaflet wording explains why your pharmacist will want you to speak to your midwife or GP rather than simply selling you a pack.
Is there a Phenergan pregnancy category?
Not in the UK, and the United States no longer uses the old letter based system either.
The letters A, B, C, D and X were part of a former US system introduced in 1979. Promethazine was previously classified as Pregnancy Category C under that system. The US Food and Drug Administration removed the letter categories when the Pregnancy and Lactation Labeling Rule took effect on 30 June 2015. The change was made because a single letter could be misleading and did not provide enough information about the potential benefits and risks of using a medicine during pregnancy.
So, if you find a website stating that Phenergan is Pregnancy Category C, it is referring to an old US classification. That system did not apply in the UK and is no longer used in the US.
In the UK, information about medicines during pregnancy is provided through sources such as the NHS, NICE, UK Teratology Information Service (UKTIS) and the manufacturer's product information. These sources provide more detailed information than a single pregnancy category.
Promethazine to treat nausea and pregnancy sickness
Nausea and vomiting are common during pregnancy and can affect a large proportion of pregnant women. Promethazine is one of the medicines that may be considered for nausea and vomiting in pregnancy when treatment is needed.
The Royal College of Obstetricians and Gynaecologists (RCOG) describes pregnancy sickness as nausea or vomiting that usually starts during the first part of pregnancy and has no other identified cause. Symptoms commonly begin between weeks 4 and 7. For many women, they improve by around week 20.
The term "morning sickness" can be misleading because nausea and vomiting can happen at any time of day. For some women, the symptoms can also be severe enough to affect eating, drinking, work and everyday activities.
Hyperemesis gravidarum is a more severe form of pregnancy sickness. It can involve frequent vomiting, difficulty eating and drinking, dehydration and weight loss. It may require medical assessment and treatment rather than self treatment with an over the counter medicine.
Healthcare professionals may use tools such as the Pregnancy Unique Quantification of Emesis and Nausea (PUQE) score to assess the severity of symptoms. This is one reason it is important to seek medical advice when sickness is becoming difficult to manage.
For milder symptoms, some people may consider measures such as ginger. However, speak to your midwife, GP or pharmacist before taking any medicine or supplement during pregnancy, particularly if your symptoms are getting worse.
When pregnancy sickness needs urgent assessment
Contact your midwife, GP or NHS 111 for advice if you are experiencing symptoms such as:
- Being unable to keep fluids down.
- Passing very little urine or having urine that is unusually dark.
- Losing weight or feeling faint, dizzy or very weak.
- Abdominal pain, a high temperature or blood in your vomit.
- Sickness that starts for the first time after 16 weeks of pregnancy, as other causes may need to be considered.
If you are struggling with pregnancy sickness, you do not have to manage it alone. Pregnancy Sickness Support also provides information and support for people experiencing pregnancy sickness, including hyperemesis gravidarum.
Promethazine, birth defects, and respiratory depression
For many people, the main concern is whether taking promethazine during pregnancy could harm the baby. UKTIS states that promethazine is commonly used during pregnancy and that available data have not raised concerns about an increased risk of harm to the unborn baby. NHS guidance also states that there is no evidence that promethazine is harmful to the baby.
Promethazine can cross the placenta, as stated in the product information. However, the fact that a medicine crosses the placenta does not by itself mean that it is harmful to the baby.
It is also important to remember that every pregnancy has a background risk of complications and birth defects, whether or not medicines are taken. Available studies have not identified a clear increase in the risk of congenital malformations associated with promethazine exposure. Evidence has also not raised a clear concern about an increased risk of low birth weight or premature birth, although no medicine can be considered completely risk free.
The decision to use any medicine during pregnancy should therefore consider both the potential benefits and risks. Severe untreated pregnancy sickness can itself cause problems such as dehydration, weight loss and nutritional difficulties, so the risks of leaving symptoms untreated may also need to be considered.
Promethazine can cause drowsiness and other side effects. Rare blood related adverse effects have also been reported. If you develop symptoms such as an unexplained sore throat, fever or other signs of infection while taking promethazine, contact your doctor promptly.
If you are pregnant and considering Phenergan for nausea, vomiting, allergies or another reason, speak to your midwife, GP or pharmacist. They can consider your stage of pregnancy, symptoms, medical history and other medicines before advising whether it is suitable for you.
Does the stage of pregnancy change the answer?
The live advice circulating online often gets this backwards, suggesting promethazine should be avoided early and is safer later. The UK picture is closer to the opposite.
| Stage | What UK sources say |
|---|---|
| First trimester | This is when pregnancy sickness peaks, and it is precisely when guideline recommended antiemetics including promethazine are most often used. There is no UK guidance recommending routine avoidance of promethazine in the first trimester on safety grounds |
| Second trimester | Sickness has usually settled by around week 20. Promethazine may still be used for allergy or sleep problems, though other options are often preferred for those |
| Third trimester | Still used where needed, but this is where the product information carries a specific caution: the product information notes that high doses used close to delivery have been associated with prolonged neurological disturbances in newborn infants |
| Close to delivery | Some NHS formulary guidance advises caution with promethazine use during the two weeks before delivery , because of the risk of irritability and excitement in the newborn. This is a point to raise with your midwife rather than judge yourself |
Allergies and hay fever during pregnancy
Promethazine is a sedating antihistamine, so it can make you feel sleepy. Sedation is listed as a very common side effect in the Phenergan product information.
If you have hay fever during pregnancy, your doctor or pharmacist may recommend a non sedating antihistamine such as loratadine. Cetirizine is another antihistamine commonly used during pregnancy. These options may be preferred when avoiding drowsiness is important.
This does not mean that promethazine is prohibited during pregnancy. The most suitable option depends on your symptoms, medical history and other medicines. If your allergies are severe, affecting your sleep or difficult to manage, speak to your doctor or pharmacist rather than choosing a medicine based only on information online.
Sleep problems during pregnancy
Poor sleep is common during pregnancy and can have many causes, including heartburn, restless legs, needing to urinate during the night, anxiety and physical discomfort as pregnancy progresses.
Promethazine is licensed for the short term treatment of insomnia in adults, and the product information advises that it should not be used for longer than 7 days without medical advice. However, pregnancy is a time when you should discuss medicines with your healthcare professional before taking them.
If poor sleep is affecting you regularly, mention it to your midwife or GP. They can help identify what is keeping you awake and whether there is a safer or more appropriate way to manage the underlying problem.
One detail almost no article mentions
The Phenergan product information states that promethazine may interfere with some immunological urine pregnancy tests and could potentially result in a false positive or false negative result.
If you have recently taken promethazine and a home pregnancy test gives a result that does not seem to fit your circumstances, tell your GP or midwife that you have taken the medicine. They can advise whether repeat testing or further assessment is appropriate.
Promethazine and breastfeeding
The advice about promethazine during breastfeeding is more cautious in the manufacturer's product information than in NHS guidance.
The product information advises against using promethazine while breastfeeding and notes the possibility of effects such as irritability or excitement in a newborn. NHS guidance states that if your baby is healthy, promethazine can be used while breastfeeding, preferably occasionally or for a short period and after discussing it with a doctor or pharmacist.
It is not known exactly how much promethazine passes into breast milk. Available information suggests that the amount is likely to be small, and significant problems have not been commonly reported in breastfed babies. However, because promethazine can cause drowsiness, your baby may also become unusually sleepy.
Contact your doctor, pharmacist or NHS 111 if your baby becomes unusually sleepy, feeds poorly, gains weight more slowly than expected or seems unusually irritable.
NHS guidance also advises against sharing a bed with your baby while taking promethazine because of the risk associated with increased sleepiness.
If you need an antihistamine while breastfeeding, your doctor or pharmacist may recommend another option. Specialist Pharmacy Service guidance considers chlorphenamine a preferred sedating antihistamine and medicines such as cetirizine or loratadine preferred non sedating options in breastfeeding.
Why this is not a self treatment decision: consult your healthcare provider
Taken together, UK guidance and the available evidence support an individual approach to promethazine use during pregnancy. Promethazine has been used during pregnancy for many years, and available evidence has not identified a major safety concern. It is also one of the medicines that may be considered for pregnancy sickness.
However, this does not mean that you should start taking it without professional advice. Your symptoms, stage of pregnancy, medical history and other medicines all need to be considered.
- Pregnancy sickness may need assessment before treatment, particularly if you are becoming dehydrated, losing weight or struggling to keep fluids down.
- Sickness that starts after 16 weeks of pregnancy may need assessment for other possible causes.
- If treatment does not help, your healthcare professional may consider another antiemetic or a different treatment approach.
- The appropriate dose, timing and duration during pregnancy should be determined by a healthcare professional rather than copied from information intended for other uses, such as hay fever or motion sickness.
- Tell your midwife, GP or pharmacist about every medicine you take, including prescription medicines, over the counter products, supplements and herbal products. This helps them check for possible interactions.
- Promethazine can increase drowsiness when combined with other sedating medicines, and alcohol should be avoided while taking it.
Injectable promethazine is used in different clinical situations and has separate dosing, administration and safety considerations. Information about tablets or oral liquid should not be used to make decisions about injectable promethazine.
The NHS page on promethazine, pregnancy, breastfeeding and fertility is the best starting point, and it links onward to the UKTIS bumps leaflet written for exactly this question.
The specialist leaflet itself is available at Best Use of Medicines in Pregnancy, produced by the UK Teratology Information Service.
For the wider suitability picture outside pregnancy, including conditions and medicines that rule promethazine out, see our guide to who can and cannot take promethazine.
If you want to understand the effects themselves before any conversation with your midwife, our guide to Phenergan side effects covers what to expect.
You can also put a question to our clinical team, though anything relating to your pregnancy should go to your own midwife or GP, who has your full record.
Medical Disclaimer
This article provides general information and does not replace advice from your midwife, GP, obstetrician or pharmacist. It does not provide individual dosing instructions, and nothing here should be used to start, stop or change a medicine during pregnancy or while breastfeeding without professional advice.
Whether a medicine is suitable during pregnancy or breastfeeding depends on your individual circumstances, including your symptoms, stage of pregnancy, medical history and any other medicines or supplements you are taking.
Tell any healthcare professional treating you if you are pregnant, trying to conceive or breastfeeding. If you are unwell, your symptoms are getting worse or you are worried about your pregnancy, contact your maternity unit, GP or NHS 111 for advice. In an emergency, call 999.
The information in this article is based on the Summary of Product Characteristics for Phenergan tablets available through the electronic Medicines Compendium (emc), NHS guidance on promethazine, NICE Clinical Knowledge Summaries, the UK Teratology Information Service BUMPS leaflet, and RCOG Green Top Guideline No. 69. Always check the latest available guidance and product information, as recommendations can change.
