Promethazine is a sedating antihistamine used for allergies and itching, for nausea, vomiting and motion sickness, and for its strong drowsiness-causing effect. In South Africa it appears both on its own and in many combination cough and pain syrups. It must never be given to children under two years old.
What is Promethazine?
Promethazine is a first-generation antihistamine from the phenothiazine family. It blocks histamine H1 receptors, which is what makes it useful in allergy — but it also blocks several other receptor types, and those extra actions explain most of what it does.
| Receptor blocked | Effect |
|---|---|
| Histamine H1 | Reduces allergic symptoms and itching |
| H1 in the brain | Marked drowsiness and sedation |
| Dopamine | Reduces nausea and vomiting |
| Muscarinic (anticholinergic) | Dry mouth, blurred vision, constipation, urinary retention |
Crossing into the brain is the key difference from modern antihistamines. Newer ones such as cetirizine and loratadine were designed to stay out of the brain, so they treat allergy without heavy sedation. Promethazine does the opposite, and its sedation is often the reason it is chosen rather than a side effect to tolerate.
In South Africa promethazine is found:
- On its own, as a syrup (commonly 5 mg/5 ml) and as tablets, typically 25 mg.
- In combination products, most often paracetamol + codeine + promethazine syrups sold for pain and cough. Brands in this group include Medipyn, Salterpyn, Infapain Forte, Painagon and several others.
That second group matters. If you are taking a combination syrup, you are taking codeine and paracetamol as well — which brings its own risks, covered below.
What is Promethazine commonly used for?
- Allergic conditions — hay fever, allergic rhinitis, hives (urticaria) and allergic skin reactions.
- Itching, including from eczema, insect bites and chickenpox, where the sedating effect also helps sleep.
- Nausea and vomiting, including in some post-operative and medication-related settings.
- Motion sickness, taken before travel rather than after symptoms start.
- Vertigo and inner-ear-related nausea.
- Short-term sedation, including before minor procedures and occasionally for sleep difficulty.
- As part of combination cough and cold preparations, where it dries secretions and sedates.
It treats symptoms, not causes. It does not treat infection, and in allergy it does not address what you are reacting to.
For daytime allergy control in someone who needs to drive, work or study, a non-sedating antihistamine is almost always the better choice. Promethazine suits situations where sedation is acceptable or actively wanted — night-time itching being the classic example.
How Promethazine fits into this medicine category
| Group | Examples | Notes |
|---|---|---|
| Sedating antihistamines | Promethazine, chlorphenamine | Allergy, itch, nausea; marked drowsiness |
| Non-sedating antihistamines | Cetirizine, loratadine | Allergy without significant sedation |
| Anti-nausea (dopamine blockers) | Metoclopramide | Nausea and vomiting |
| Antihistamine sedatives | Promethazine, diphenhydramine | Occasional short-term sleep aid |
| Benzodiazepines | Diazepam | Anxiety, muscle spasm; controlled |
| Tricyclics | Amitriptyline | Nerve pain, mood, sleep |
| Anti-epileptics | Carbamazepine | Seizures, some nerve pain |
Promethazine sits unusually across several of these roles, which is why it turns up in such different products. See the mental health, nerve and neurological medicines hub.
What to check before using Promethazine
Never give promethazine to a child under two years old. This is an absolute restriction, not a precaution. It has caused fatal respiratory depression in very young children. Be especially careful with combination syrups marketed for children’s pain or cough — check the ingredients, because promethazine is not always prominent on the front of the pack.
Check whether your product also contains codeine and paracetamol. Many South African promethazine syrups do. That means opioid cautions apply, that you must not take other paracetamol alongside it, and that it should not be used for more than a few days.
Speak to a pharmacist or doctor first if you:
- Are giving it to any child, where age and weight determine suitability.
- Are elderly. Sedation, confusion, falls and urinary retention are all more likely.
- Have breathing problems — asthma, COPD or sleep apnoea.
- Have glaucoma, particularly narrow-angle.
- Have prostate enlargement or difficulty passing urine.
- Have epilepsy.
- Have liver or kidney disease.
- Have heart rhythm problems, or take medicines that affect the QT interval.
- Take any other sedating medicine — opioids, benzodiazepines, sleeping tablets, or alcohol.
- Take an MAOI antidepressant.
- Are pregnant or breastfeeding.
Do not drive or operate machinery. The sedation is substantial and can persist into the following day.
Possible cautions and when to ask a pharmacist or doctor
Common effects are drowsiness, dry mouth, blurred vision, dizziness, constipation and difficulty passing urine. In children, promethazine sometimes causes the opposite of sedation — restlessness and agitation.
Seek medical attention urgently if you notice:
- Slow, shallow or difficult breathing, or unusual difficulty waking someone — especially a child, or anyone also taking an opioid.
- Muscle stiffness, tremor, restlessness, or uncontrolled movements of the face, tongue or limbs.
- High fever with rigidity, confusion and sweating — a rare but serious reaction.
- A seizure.
- Yellowing of the eyes or skin.
- Swelling of the face, lips or tongue, or difficulty breathing.
- Severe rash or blistering.
- Inability to pass urine.
- Palpitations or fainting.
Promethazine-and-codeine syrups are misused recreationally, sometimes mixed into soft drinks. This is genuinely dangerous rather than merely inadvisable: the combination suppresses breathing, the effect deepens with alcohol or other sedatives, and deaths have resulted. If you or someone you know is using these syrups outside their intended purpose, that is worth raising with a doctor or pharmacist.
Promethazine can also make skin more sensitive to sunlight — use sun protection during a course.
See a doctor if allergy symptoms persist, if nausea or vomiting continues beyond a couple of days or comes with severe pain, if you cannot keep fluids down, or if you find yourself relying on it to sleep.
Related medicine guides
- Browse Mental Health, Nerve & Neurological Medicines guides
- Read: Trepiline used for
- Read: Nurika used for
Frequently asked questions
What is promethazine used for? Allergies and itching, nausea, vomiting and motion sickness, and short-term sedation. It is a sedating antihistamine.
What is promethazine 25 mg used for? The common tablet strength, used for allergic symptoms, itching, nausea and motion sickness, and sometimes for its sedating effect. Follow the instructions you were given.
Are promethazine tablets a sleeping tablet? They are not a dedicated sleeping medicine, but the drowsiness is marked and promethazine is sometimes used short-term for sleep. It is not intended for long-term use for that purpose.
Can I give it to my child? Never under two years old. Above that, ask a pharmacist or doctor, and check combination syrups for what else they contain.
Does it make you sleepy? Yes, markedly, and the effect can carry into the next day. Do not drive or operate machinery.
Can I drink alcohol with it? No. Alcohol adds substantially to the sedation and to the risk of suppressed breathing.
Is promethazine an antibiotic? No. It has no effect on infection.
Why is it in cough and pain syrups? It sedates and dries secretions, and is combined with paracetamol and codeine in several South African products. Check the label — those extra ingredients carry their own cautions.