What does promethazine do?

Promethazine is a first‑generation antihistamine with sedating effects. It works by blocking histamine H1 receptors and also has anticholinergic properties, which helps with motion sickness and nausea.

What it’s used for (common uses)
- Allergy symptoms: runny nose, sneezing, itching, watery eyes
- Nausea and vomiting: especially from motion sickness, after surgery, or other causes
- Sedation: short-term sleep aid or premedication in some settings (usually short courses)

How it’s given
- Available as tablets, syrup, suppositories, and injections (the IV form is generally avoided due to risk of tissue injury; dosing and route depend on age and condition)

Common side effects
- Drowsiness or dizziness
- Dry mouth, blurred vision, constipation, urinary retention
- In children, it can sometimes cause agitation instead of drowsiness

Important safety notes
- More likely to cause dizziness and confusion in older adults
- Can enhance effects of alcohol and other sedatives
- Not suitable for everyone (e.g., may worsen glaucoma, urinary retention, certain heart or nerve conditions)
- Often avoided in children under 2 years; use with caution in young children and the elderly
- Do not use IV promethazine unless specifically directed by a clinician (risk of severe tissue injury)

If you have a specific use in mind (e.g., travel sickness, post-surgery nausea, allergy relief), I can tailor the details and discuss typical dosing, risks, and interactions.