Promethazine Hydrochloride 25mg - 56 Tablets

What is promethazine?

Promethazine hydrochloride is a drowsy antihistamine belonging to a group of medicines called phenothiazines. It is commonly used to treat allergies and travel sickness, but it may also be used for short-term insomnia and nausea relief.

Unlike some newer antihistamines, promethazine can cross into the brain, which is why it may make you feel sleepy. But don't worry, it's safe when used as directed. In fact, this drowsy effect may be one of the benefits of the treatment, depending on what symptoms you're looking to relief.

What is promethazine used for?

Promethazine may be used to help manage:

• hay fever and allergic reactions
• skin allergies and itching
• feeling sick (nausea) and being sick (vomiting)
• motion sickness and travel sickness
• short-term sleep problems

How does promethazine work?

Promethazine works by blocking the action of histamine, a chemical released by the body during allergic reactions.

By blocking histamine receptors, promethazine can help reduce symptoms like:

• sneezing
• itching
• skin rashes
• watery eyes

Promethazine also affects certain brain receptors involved in wakefulness and nausea, which is why it can help with sleep problems and motion sickness.

How long does promethazine take to work?

The exact amount of time promethazine takes to work depends on your individual response to the treatment, and what symptoms you're trying to deal with. Usually, it begins working within:

• 20–30 minutes for the drowsy (sedative) effects
• around 1–2 hours to clear other symptoms

You can find out more about how long antihistamines take to work in our expert guide.

How long does promethazine stay in your system?

The effects of promethazine may last around 4-6 hours for symptom relief, and longer for drowsiness, depending on your reaction to the treatment.

How to take promethazine hydrochloride 25mg

Always take promethazine exactly as directed by your prescriber or the patient information leaflet.

The tablets should be swallowed whole with water and may be taken with or without food.

How frequently you take the tablets depends on what you want to treat.

For allergies:

• Adults: start by taking one 25mg tablet at night. If necessary, increase the dose to two tablets a day.
• Children (6-10 years old): one 25mg tablet should be given at night. Do not give children more than one tablet a day.

For the prevention of nausea and vomiting due to travel sickness:

• Adults: take one 25mg tablet the night before a journey. If necessary, take another dose 6-8 hours after the first.

You can find out more guidance on how many antihistamines you should take in 24 hours with our guide.

Promethazine maximum dosage for adults

The maximum dose of promethazine for adults depends on the condition being treated and individual medical suitability.

Exceeding the recommended dose may increase your risk of:

• severe drowsiness
• confusion
• breathing difficulties
• cardiovascular side effects

Never take more than prescribed or stated in the patient information leaflet.

Promethazine side effects

Like all medicines, promethazine can cause side effects, although not everyone experiences them.

Common side effects:

• drowsiness or sedation
• dry mouth
• dizziness
• blurred vision

Less common side effects:

• confusion
• restlessness
• headache
• difficulty urinating

Older adults may be more sensitive to sedative side effects.

When to seek medical help

Seek urgent medical advice if you experience:

• difficulty breathing
• severe allergic reactions
• irregular heartbeat
• seizures
• severe confusion or hallucinations

You should also seek advice if side effects become severe or persistent.

When not to use promethazine

Promethazine may not be suitable if you:

• are allergic to promethazine or phenothiazines
• have severe breathing problems
• have glaucoma
• have severe liver disease
• are taking certain medicines that interact with promethazine

Always inform your healthcare provider about any existing conditions or medications.

Promethazine and alcohol

You should avoid drinking alcohol while taking promethazine.

Both alcohol and promethazine can cause you to feel sleepy, and combining them may increase your risk of:

• excessive drowsiness
• dizziness
• impaired coordination
• breathing difficulties

Promethazine and pregnancy

If you are pregnant, breastfeeding, or trying to conceive, speak to a healthcare professional before taking promethazine.

Promethazine may sometimes be used during pregnancy under medical supervision, particularly for nausea, but suitability should always be assessed individually.

How to order promethazine tablets with Chemist4U

When ordering promethazine hydrochloride with Chemist4U, we'll ask you a few quick questions to make sure the treatment is safe and suitable for you.

If it is, we'll send it out in fast, discreet delivery, straight to your door.

Storage information

• Store below 25°C.
• Keep in the original packaging.
• Keep out of sight and reach of children.
• Do not use after the expiry date.

Alternatives to promethazine tablets

Alternative treatments depend on the condition being treated. We can help you find the best antihistamines for your needs, including non-drowsy options like cetirizine or loratadine.

Find out whether you can take two antihistamines at the same time with our guide.

Frequently asked questions about promethazine hydrochloride

Is promethazine addictive?

Promethazine is not considered physically addictive, but it should only be used as directed.

Does promethazine make you sleepy?

Yes. Promethazine is a sedating antihistamine and commonly causes drowsiness.

Can promethazine hydrochloride be used for anxiety?

Promethazine is not primarily licensed for anxiety treatment, but its sedative effects may sometimes help calm agitation or anxiety symptoms under medical supervision.

Is promethazine a strong sedative?

Promethazine can have significant sedative effects in some people, particularly at higher doses or when combined with alcohol or other sedating medicines.

Does promethazine cause weight gain?

Weight gain is not a common side effect, although changes in appetite or sedation-related lifestyle changes may affect some individuals.

Sources

• Promethazine hydrochloride Patient Information Leaflet. MHRA. [Accessed 5 August 2026].
• Promethazine. NHS. [Accessed 6 August 2026]
• Antihistamines. NHS. [Accessed 6 August 2026]
• Insomnia. NHS. [Accessed 6 August 2026]
• Motion sickness. NHS. [Accessed 6 August 2026]
• Promethazine hydrochloride. Patient.info. [Accessed 6 August 2026]