Promethazine hydrochloride is an antihistamine with sedative and antiemetic (anti-nausea) properties. It’s a phenothiazine derivative that blocks histamine H1 receptors and also has anticholinergic effects. It’s sold under brand names like Phenergan and is available in tablets, syrup, suppositories, and injectable forms.
What it’s used for
- Allergy symptoms (itching, runny nose, hives)
- Nausea and vomiting (antiemetic)
- Motion sickness
- Sedation before or after procedures
- Sometimes as a sleep aid (short-term)
Common dosing (adult guidelines; always follow the product label or your clinician)
- Allergy or antiemetic: 25 mg every 4–6 hours as needed; max about 100 mg per day.
- Nausea/vomiting: 12.5–25 mg every 4–6 hours as needed.
- Motion sickness: 25 mg taken 30–60 minutes before travel.
- Sedation: can be higher, but this is typically under medical direction.
Important safety notes
- Do not use IV promethazine. Intravenous administration is associated with severe tissue injury and is generally avoided; IM use is more common if needed.
- Not recommended for children under 2 years due to risk of serious breathing problems; use with caution in older children and avoid use in very young or frail patients unless directed by a doctor.
- Elderly patients are more sensitive to side effects like confusion, dizziness, and falls.
- Avoid alcohol and other central nervous system depressants while using promethazine, as they can enhance drowsiness and sedation.
- Can cause drowsiness, dizziness, dry mouth, blurred vision, constipation, and urinary retention. Photosensitivity can occur.
Warnings and interactions
- Contraindications include known hypersensitivity to promethazine or other phenothiazines, and certain combinations that raise risk of dangerous effects.
- May interact with other CNS depressants (sedatives, opioids, alcohol), MAO inhibitors, anticholinergic drugs, and other medicines that affect heart rhythm.
- Promethazine can prolong QT interval in some people, especially with other QT-prolonging drugs or electrolyte abnormalities.
Pregnancy and breastfeeding
- Generally categorized as a C (risk cannot be ruled out); use only if clearly needed and prescribed by a clinician. May pass into breast milk; discuss with a healthcare provider if you’re breastfeeding.
If you’d like, tell me:
- Are you asking about a specific form (tablet, syrup, suppository, injectable) or a particular indication?
- Your age and any other medicines you’re taking (especially sedatives, antidepressants, or heart meds)?
- Whether this is for you or someone else (and any pregnancy/lactation status)?
I can tailor dosing, safety tips, and potential alternatives to your situation.