Promethazine — what it does, how to use it safely

Promethazine is a widely used antihistamine that also fights nausea and helps with motion sickness and sleep. It works fast for many people, but it can cause strong drowsiness and has serious risks in some groups. Want to know when it’s helpful and when to be careful? Keep reading.

What promethazine is used for and how it’s given

People take promethazine for allergy symptoms (sneezing, itching), nausea and vomiting, motion sickness, and as a short-term sleep aid. It comes as tablets, syrup, suppositories, and in some places as an injection. Suppositories are useful if you’re vomiting and can’t keep pills down.

Typical adult oral dosing is 12.5–25 mg every 4–6 hours as needed, with a usual max around 100 mg per day. For motion sickness some people take 25–50 mg about an hour before travel. Dosages for children are weight-based and must be set by a doctor. Important: promethazine should not be given to children under 2 years — the risk of severe breathing problems is high.

Side effects, interactions, and practical safety tips

Common side effects include drowsiness, dizziness, dry mouth, blurred vision, and constipation. Because it sedates, avoid driving or operating heavy machinery until you know how it affects you. Older adults often feel stronger sedation and may also have confusion or falls.

Serious issues to watch for: slowed breathing, extreme sleepiness, severe low blood pressure, or signs of an allergic reaction. If any of these happen, get medical help right away.

Promethazine interacts with many drugs. Don’t mix it with alcohol, opioids, benzodiazepines, or other strong sedatives — the combined sedation can be dangerous. Drugs that affect the heart rhythm (QT interval) or strong anticholinergic medicines can add risk. If you’re on MAO inhibitors or have liver disease, check with your doctor first.

Pregnancy and breastfeeding: talk to your healthcare provider. Promethazine can affect newborns if used during labor and may pass into breast milk, causing drowsiness in infants.

Practical tips: get a clear dose from your prescriber, use the suppository form if vomiting, store medication out of reach of children, and never give promethazine to a baby or toddler. If sedation is a problem, ask about alternatives like meclizine for motion sickness or ondansetron for severe nausea.

If you’re buying medication online, pick a licensed pharmacy and keep records of prescriptions. Any unusual symptoms after starting promethazine deserve a quick call to your doctor or pharmacist.

Got questions about your dose or a drug interaction? Ask your pharmacist or prescriber — they can give advice tailored to your health and other medicines.