If you are comparing Phenergan with loratadine, you will often find pages trying to tell you which one is better. However, that is not really the most useful way to look at these medicines.
Both are antihistamines, but they have different properties and are licensed for different conditions. Phenergan contains promethazine, which can cause drowsiness, while loratadine is generally considered a non drowsy antihistamine at the recommended dose.
The better question is: which medicine is more suitable for what you need it for? This guide explains what each medicine is licensed for in the UK, how they differ, their possible side effects, and why one may be more appropriate than the other in certain situations.
Key things to know
- Phenergan contains promethazine, a first generation sedating antihistamine. Loratadine is a second generation antihistamine that is generally considered non drowsy at the recommended dose, although some people may still experience drowsiness.
- They are not licensed for exactly the same conditions. Loratadine is licensed for allergic rhinitis and chronic idiopathic urticaria. Phenergan also has licensed uses for conditions such as motion sickness and the short term treatment of insomnia in adults.
- Loratadine is not licensed as a treatment for motion sickness. If motion sickness is your main concern, speak to a pharmacist about which medicine may be appropriate.
- Loratadine is usually taken once a day, and its antihistamine effects can last for around 24 hours. The effects of promethazine may last for up to 12 hours, which can contribute to next day drowsiness in some people.
- Phenergan is a Pharmacy (P) medicine in the UK, while some loratadine products are available without a prescription from pharmacies and other retailers.
- Do not take two antihistamines together unless a doctor or pharmacist has advised you to do so. Combining medicines can increase the risk of side effects, including drowsiness.
The honest answer to "which works better"
There is no simple winner. For allergic symptoms that both medicines may be used to treat, such as sneezing, a runny nose, itchy eyes and hives, there is no clear evidence that one consistently works better for everyone.
The main differences are often related to how the medicines affect you and what you need them for. For example, loratadine may be more convenient if you want an antihistamine that is less likely to make you sleepy, while promethazine may be considered when its other licensed uses are relevant.
Your age, health conditions, other medicines, symptoms and the need to stay alert can all affect which option is more suitable. A pharmacist can help you make that decision based on your individual circumstances rather than relying on a general comparison online.
Phenergan and loratadine oral antihistamines side by side
| Phenergan (promethazine hydrochloride) | Loratadine | |
|---|---|---|
| Class | First generation sedating antihistamine, a phenothiazine derivative | Second generation antihistamine, selective peripheral H1 activity |
| Strengths in the UK | 10mg and 25mg tablets, plus a 5mg/5ml elixir | 10mg tablets, plus syrup formulations |
| Licensed uses | Allergic conditions of the upper respiratory tract and skin including allergic rhinitis, urticaria and anaphylactic reactions to drugs and foreign proteins, severe allergic reaction; as an antiemetic; short term treatment of insomnia in adults; paediatric sedation | Symptomatic treatment of allergic rhinitis and chronic idiopathic urticaria only |
| Sedation | Sedation or somnolence is the only side effect classed as very common | No clinically significant sedative properties at the recommended dose. Somnolence reported in 1.2 per cent of trial patients in excess of placebo |
| Onset | No onset figure is published in the UK product information. NHS guidance says symptoms usually improve within about 20 minutes | Antihistamine effects seen within one to three hours, peaking at eight to twelve hours; cetirizine may relieve symptoms within 30 to 60 minutes |
| Duration | Duration of action may be up to 12 hours | Effect lasts in excess of 24 hours after a single dose |
| Dosing pattern | Product information sets a maximum for allergy use; not to be used longer than seven days without medical advice | One tablet once daily |
| Tolerance | Sedative effect tends to fade with continued nightly use | No evidence of tolerance after 28 days of dosing |
| Legal category | Pharmacy medicine (P), sold under a pharmacist's supervision | Available both as a pharmacy medicine and on the general sales list, depending on the product |
| Driving | Do not drive or use machinery if you feel sleepy, dizzy or your vision is blurred | Clinical trials assessing driving found no impairment. Negligible influence on driving |
| Minimum age | Contraindicated under six years of age | Tablet not suitable under six years or under 30kg; syrup or other oral antihistamines formulations may be used depending on age and product |
Histamine contributes to many allergy symptoms, including swelling, itching and a runny nose, which is why antihistamines are used to help relieve them .
Why one makes you drowsy and the other is a non drowsy antihistamine
Both promethazine and loratadine work by blocking H1 histamine receptors. The main difference is how readily they enter the brain.
Promethazine can cross the blood brain barrier and block histamine receptors in the brain as well as those involved in allergy symptoms. Histamine also has a role in maintaining wakefulness, so blocking its action in the brain can cause drowsiness. Promethazine also has anticholinergic effects, which may contribute to side effects such as dry mouth, constipation and blurred vision.
Loratadine is a second generation antihistamine designed to have limited penetration into the central nervous system. At the recommended dose, it is generally considered non drowsy, although some people may still experience sleepiness. Its product information also indicates that it does not have clinically significant anticholinergic properties at the recommended dose.
This difference helps explain why promethazine may be used for some conditions where a sedating effect is relevant, while loratadine is generally chosen when allergy symptoms need treating without significant daytime drowsiness.
What each is actually licensed to treat
The two medicines are not interchangeable. Although they are both antihistamines, their licensed uses are different.
Where they genuinely overlap
Both medicines are used to treat allergic conditions. Depending on the specific product, these include allergic rhinitis and urticaria.
If your symptoms include sneezing, a runny or blocked nose, itchy or watery eyes, or an itchy raised rash, either medicine may be an option for allergy symptoms. The choice can depend on factors such as how much drowsiness you can tolerate, your other medicines and your individual health circumstances.
Where only Phenergan is licensed
Promethazine has licensed uses beyond allergy treatment. It is also used for nausea and vomiting, including the prevention and treatment of motion sickness, and Phenergan tablets are licensed for the short term treatment of insomnia in adults.
Promethazine may also be used for nausea and vomiting during pregnancy when a healthcare professional considers it appropriate. Loratadine does not have these same licensed uses.
What loratadine cannot do
Loratadine is not licensed as a treatment for motion sickness or insomnia. Taking loratadine for a journey because you expect it to prevent motion sickness is therefore not the same as taking an antihistamine specifically indicated for that purpose.
Some medicines used for motion sickness work partly through their effects on the central nervous system. This is also why a non drowsy antihistamine such as loratadine should not be expected to have the same sedating effects as promethazine.
If you are looking for a medicine for travel sickness or sleep rather than allergies, speak to a pharmacist about which option is appropriate.
Phenergan vs loratadine side effects compared
The side effect profiles of these two antihistamines are quite different, particularly when it comes to drowsiness.
For loratadine, clinical trial data provide specific frequency estimates for some adverse reactions. In the product information, adverse reactions occurred in a small proportion of patients above the rate seen with placebo. Reported reactions included somnolence, headache, increased appetite and insomnia. The exact frequency can vary between studies and product information, so it is best to refer to the current leaflet for the specific loratadine product you are using.
For promethazine, sedation or somnolence is listed as a very common adverse effect in the product information. Other possible effects include dry mouth, constipation, dizziness, blurred vision and difficulty passing urine. Several of these effects have a frequency listed as "not known", which means there is not enough reliable information to calculate a percentage.
This is important when comparing the two medicines. A lack of a published percentage for a promethazine side effect does not mean that the effect cannot occur. It means that a reliable frequency estimate is not available in the product information. Avoid websites that present precise percentages for these effects without identifying a reliable source.
If you are taking antihistamines, check with a pharmacist before combining them with alcohol or other medicines .
| Phenergan | Loratadine | |
|---|---|---|
| Most likely effect | Sedation, classed as very common | Somnolence, 1.2 per cent above placebo |
| Anticholinergic effects | Dry mouth, constipation, urinary retention, blurred vision, all frequency not known | No clinically significant anticholinergic properties at the recommended dose |
| Older adults | Particularly susceptible to anticholinergic effects and to confusion | No equivalent warning in the product information |
| Other cautions | QT prolongation risk; photosensitivity; Fever or a sore throat may rarely indicate a blood disorder and should be assessed urgently | Dose adjustment specified for severe liver impairment |
| Alcohol | Should be avoided completely | No equivalent absolute warning, though sedating effects should still be considered |
Can you take loratadine and Phenergan together?
This is a common question, but there is no simple yes or no answer for everyone.
In some situations, a healthcare professional may recommend using a non drowsy antihistamine during the day and a sedating antihistamine at night. This may sometimes be considered for conditions such as chronic urticaria when itching is affecting sleep. However, this should only be done on the advice of a pharmacist or prescriber who knows your circumstances.
Do not assume that taking two antihistamines will automatically provide better relief. Combining medicines can increase your exposure to side effects without necessarily providing additional benefit. NHS guidance also advises against taking promethazine with other sedating antihistamines, such as chlorphenamine or diphenhydramine.
It is also easy to take more than one antihistamine accidentally. Some cold and flu products contain antihistamines, so always check the ingredients before taking them alongside Phenergan or loratadine.
If one antihistamine is not controlling your symptoms, speak to a pharmacist. They can help work out whether you need a different medicine, another treatment or further assessment.
Phenergan vs loratadine for hives and itching
Chronic idiopathic urticaria refers to hives that continue or recur for more than 6 weeks. Both promethazine and loratadine are licensed for urticaria and may help relieve symptoms such as itching and hives.
However, chronic hives can require treatment over a longer period. Phenergan is intended for short term use and its product information advises against using it for longer than 7 days without medical advice. Loratadine, on the other hand, is a non drowsy antihistamine commonly used for longer term allergy management.
There are also other antihistamines that may be considered for chronic urticaria. Fexofenadine 180mg is available as a Pharmacy medicine in the UK for adults and children aged 12 years and over with chronic idiopathic urticaria, following a pharmacist's assessment.
If hives keep returning, do not rely on self treatment indefinitely. Persistent hives or swelling may have an underlying cause that needs assessment, and a GP or pharmacist can help you decide what to do next.
Phenergan or loratadine for hay fever
For daytime hay fever, a non drowsy antihistamine is often a practical choice, particularly if you need to work, study, drive or stay alert.
Loratadine, cetirizine and fexofenadine are commonly used antihistamines for seasonal allergy symptoms. NHS guidance also notes that a doctor or pharmacist may recommend a non drowsy option such as loratadine for hay fever because promethazine can cause drowsiness.
If your hay fever is affecting your sleep or daily activities, you need antihistamines regularly for a long period, or you are not sure what is triggering your symptoms, speak to a pharmacist or GP. You may need a different treatment approach rather than simply increasing or changing antihistamines.
Promethazine may have a role when its other licensed uses are relevant, such as motion sickness, or when a sedating effect is acceptable. However, it is not generally the first choice for managing hay fever throughout the allergy season because of its sedating effects and short term use restrictions.
The other names people search alongside these two
Several products appear in searches on this comparison but are not UK products, or are not comparable medicines at all.
| Name searched | What it actually is | UK position |
|---|---|---|
| Fexofenadine (Allevia, Telfast) | Second generation non drowsy antihistamine | 120mg available on general sale for hay fever in adults and children 12 and over. 180mg is a pharmacy medicine for chronic idiopathic urticaria |
| Polaramine | Dexchlorpheniramine, a sedating antihistamine | Not marketed in the UK under this name. The comparable sedating antihistamine sold here is chlorphenamine |
| Allersoothe 25 | An Australian brand of promethazine 25mg | The same active ingredient as Phenergan, sold under a different name in a different country. Not a separate medicine |
| Atarax | Hydroxyzine, a sedating antihistamine | Prescription only in the UK, so not something to self select. The MHRA issued restrictions in April 2015 over a risk of QT interval prolongation and Torsade de Pointes, reducing the maximum adult daily dose and advising against use in people with QT risk factors |
| Reglan | Metoclopramide, a dopamine antagonist antiemetic | An American brand name. Metoclopramide is prescription only in the UK, is not an antihistamine, and carries MHRA restrictions on duration of use |
| Aloxi | Palonosetron, an intravenous 5-HT3 antagonist | A hospital medicine used mainly for chemotherapy induced nausea. It is not comparable to an over the counter antihistamine |
If a comparison you have read treats any of these as an equivalent swap for Phenergan or loratadine, that is a signal the content was not written for a UK reader.
Cost and availability in the UK
Loratadine is widely available in the UK and many products can be bought without a prescription. Some loratadine products are on the General Sales List, which means they can be sold in places such as supermarkets and other retailers, as well as pharmacies. Generic versions are also widely available and may cost less than branded products.
Phenergan is a Pharmacy (P) medicine. It is supplied under the supervision of a pharmacist, who may ask about your symptoms, health conditions and other medicines before deciding whether it is suitable for you.
This check is useful because promethazine has specific contraindications, precautions and potential interactions that need to be considered before use.
Price should not be the main factor when choosing between Phenergan and loratadine. They are not simply two versions of the same medicine. Their licensed uses, effects and side effect profiles are different, so the more suitable option depends on what you are trying to treat and your individual circumstances.
Medical Disclaimer
This article provides general information and does not replace advice from a qualified healthcare professional. It does not provide individual dosing instructions, and nothing here should be used to start, stop, combine or change how you take any medicine without professional advice.
Whether a medicine is suitable depends on individual factors, including your age, medical history, pregnancy or breastfeeding status and any other medicines or supplements you take. Effects and side effects can also vary between individuals. No medicine discussed in this article is presented as universally better than another.
Always read the patient information leaflet supplied with your medicine. If you are unwell or unsure about your treatment, speak to a pharmacist, your GP or NHS 111. In an emergency, call 999.
The information in this article is based on the UK Summaries of Product Characteristics for Phenergan tablets and loratadine 10mg tablets available through the electronic Medicines Compendium (emc), NHS guidance on promethazine, and relevant MHRA publications. Always check the latest product information and official guidance, as recommendations and product availability can change.
