promethazine

Adjunctive therapy

Brands: PHENERGAN

Last reviewed 2025-12-30

Reviewed by PsychMed Editorial Team.

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Quick answers

What is promethazine?
Promethazine (brand Phenergan) is a sedating first-generation antihistamine and phenothiazine derivative used for allergy symptoms, nausea/vomiting, motion sickness, and sedation (label).
What is PHENERGAN?
PHENERGAN is a brand name for promethazine.
What is PHENERGAN (promethazine) used for?
Label indications include: Allergy symptoms, nausea/vomiting, motion sickness, and sedation (label; product-dependent).
What drug class is PHENERGAN (promethazine)?
Sedating first-generation antihistamine (H1 antagonist) and phenothiazine derivative with anticholinergic/antiemetic properties; used for allergy symptoms, nausea, motion sickness, and sedation.
What strengths does PHENERGAN (promethazine) come in?
Oral tablets: 12.5 mg, 25 mg, 50 mg (label).

Snapshot

Class: Adjunctive therapy
Common US brands: PHENERGAN
Therapeutic drug monitoring not routinely recommended.
Last reviewed: 2025-12-30

Label indications

Allergy symptoms, nausea/vomiting, motion sickness, and sedation (label; product-dependent).

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Clinical Highlights

Promethazine (brand Phenergan) is a sedating first-generation antihistamine and phenothiazine derivative used for allergy symptoms, nausea/vomiting, motion sickness, and sedation (label). Promethazine is strongly Anticholinergic and sedating. Those effects can be clinically useful for nausea with insomnia overlap, but they also increase confusion, constipation, urinary retention, and falls risk, especially in older adults and polypharmacy (Beers/clinical).

Black box warning: promethazine should not be used in children under 2 years because of the potential for fatal respiratory depression; caution is also emphasized in older children, especially with other respiratory depressants (label).
Because of anticholinergic burden and respiratory/CNS depression risk, promethazine is not a preferred long-term hypnotic. If used for sleep, treat it as a short, symptom-targeted course and avoid “polypharmacy creep” (clinical).
The compare view, promethazine evidence feed, and promethazine print page can help weigh sedating antihistamines and safer alternatives.

Dosing & Formulations

Oral tablets: 12.5 mg, 25 mg, 50 mg (label). Dosing depends on the indication (allergy vs motion sickness vs nausea vs sedation). Labels often emphasize using the smallest dose adequate to relieve symptoms (label).

For sedation, labeling includes bedtime doses (e.g., 25–50 mg in adults, product-dependent). Use the lowest effective dose and avoid combining with other sedatives when possible (label/class).
Oral onset is about 20 minutes; effects typically last 4–6 hours (up to 12 hours), so next-day impairment can occur (label).

Monitoring & Risks

CNS/respiratory depression: risk rises with alcohol, opioids, benzodiazepines, sleep medications, and sleep apnea; avoid stacking sedatives when possible (label/class). Anticholinergic effects (dry mouth, constipation, urinary retention, blurred vision): higher risk in older adults and those with urinary obstruction or glaucoma (Beers/clinical).

Cognitive effects: confusion and delirium can occur, especially in older adults; Beers Criteria guidance generally supports avoiding chronic use when possible (Beers).
Phenothiazine-class adverse effects can occur (extrapyramidal symptoms, dystonia, rarely NMS); reassess if abnormal movements, rigidity, or fever emerge (label/class).

Drug Interactions

Additive CNS/respiratory depression with alcohol, opioids, benzodiazepines, sedating antipsychotics, and other hypnotics; avoid combinations when possible and use the lowest effective doses with explicit counseling (label/class). Additive anticholinergic burden with tricyclic antidepressants, low-potency antipsychotics, and bladder antimuscarinics increases delirium and urinary retention risk (clinical).

Practice Notes

Promethazine is often best reserved for labeled uses (nausea, motion sickness, allergy symptoms) rather than as a default insomnia medication. In older adults or high-fall-risk patients, consider alternatives with lower anticholinergic burden when feasible (Beers).

If sleep is the primary complaint, prioritize CBT-I and consider evidence-backed insomnia options (e.g., DORAs, ramelteon, low-dose doxepin) rather than sedating antihistamine polypharmacy.
If promethazine is used, document indication, duration, and a stop plan to reduce refill momentum and inadvertent long-term use.

References

Promethazine hydrochloride tablets prescribing information — DailyMed (2025)
2023 American Geriatrics Society Updated Beers Criteria for Potentially Inappropriate Medication Use in Older Adults — Journal of the American Geriatrics Society (2023)
Pharmacokinetics of promethazine and its sulphoxide metabolite after intravenous and oral administration to man — British Journal of Clinical Pharmacology (1983)
Promethazine (StatPearls) — StatPearls Publishing (NCBI Bookshelf) (2025)