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What Is Promethazine?

Promethazine is a prescription first-generation antihistamine with sedating and antiemetic effects. It is used for selected allergic conditions, nausea and vomiting, motion sickness, and sedation in certain medical settings. Promethazine belongs to the phenothiazine class and is associated with the brand name Phenergan. It is available in oral, rectal, and injectable formulations, each with separate instructions. Promethazine must not be given to children younger than two years because it can cause fatal respiratory depression. Its sedating and anticholinergic effects also require caution in older patients.

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What Is Promethazine?

Promethazine is a prescription first-generation antihistamine with sedating and antiemetic effects. It is used for selected allergic conditions, nausea and vomiting, motion sickness, and sedation in certain medical settings. Promethazine belongs to the phenothiazine class and is associated with the brand name Phenergan. It is available in oral, rectal, and injectable formulations, each with separate instructions. Promethazine must not be given to children younger than two years because it can cause fatal respiratory depression. Its sedating and anticholinergic effects also require caution in older patients.

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How Does Promethazine Work?

Promethazine blocks histamine H1 receptors, reducing symptoms associated with allergic reactions, including itching, sneezing, and a runny nose. It also affects central nervous system pathways involved in nausea, vomiting, and motion sickness. Its activity at other receptors contributes to sedation and anticholinergic effects such as dry mouth, blurred vision, and constipation. Promethazine can depress breathing, especially when combined with opioids, alcohol, or other sedating medications. It does not treat the underlying cause of every allergic or gastrointestinal condition.

What Conditions Does Promethazine Treat?

Promethazine is approved for selected allergic conditions, including allergic rhinitis, allergic conjunctivitis, and certain skin reactions. It is also used to prevent or control motion sickness, nausea and vomiting, and sedation related to certain medical or surgical procedures. Some formulations have additional anesthesia-related uses. Promethazine is not intended to treat lower respiratory tract symptoms such as asthma. It is contraindicated in children younger than two years, and use in older children requires careful assessment. Pediatric vomiting should not routinely be treated with promethazine unless clinically justified.

How Should Promethazine Be Taken?

Promethazine dosing depends on the formulation, age, and indication. For motion sickness, adults may receive 25 mg orally before travel, with further doses according to the prescribed schedule. Allergy and nausea treatment can involve different doses and dosing intervals. Oral solutions should be measured using a suitable medication-measuring device. Promethazine should not be administered to children younger than two years. Injectable formulations require specific precautions because improper administration can cause severe tissue injury. Patients should avoid alcohol and other sedating substances and should not drive until they know how the medication affects them.

What Are the Side Effects and Warnings of Promethazine?

Common adverse effects include drowsiness, dizziness, dry mouth, blurred vision, constipation, and impaired coordination. Promethazine carries a boxed warning for potentially fatal respiratory depression in children younger than two years. Other serious risks include severe sedation, seizures, abnormal movements, neuroleptic malignant syndrome, and allergic reactions. Injectable promethazine can cause severe tissue injury, including gangrene, if administered improperly. Opioids, alcohol, and other central nervous system depressants increase breathing-related risks. Patients should seek immediate care for slowed breathing, unresponsiveness, severe confusion, or symptoms of a serious allergic reaction.

Common Questions About Promethazine

Is promethazine the same as Phenergan?

Yes. Phenergan is a brand name associated with promethazine, a sedating first-generation antihistamine.

Can promethazine treat nausea and vomiting?

Yes. Promethazine is approved for selected causes of nausea and vomiting, including motion sickness and certain medical or surgical situations.

Can children younger than two years take promethazine?

No. Promethazine is contraindicated in children younger than two years because it can cause potentially fatal respiratory depression.

Can promethazine cause dry eyes or blurred vision?

Yes. Its anticholinergic effects can contribute to blurred vision and dryness. Persistent symptoms should be discussed with an eye care professional, particularly by contact lens wearers.

References

DailyMed - PROMETHAZINE HYDROCHLORIDE tablet. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=e6d940f8-fa1a-4a75-b4fc-2cbbaf7a0488. Date Accessed November 2, 2026.

Promethazine. LiverTox. https://www.ncbi.nlm.nih.gov/books/NBK548427/. Date Accessed November 2, 2026.

Promethazine. MedlinePlus. https://medlineplus.gov/druginfo/meds/a682284.html. Date Accessed November 2, 2026.

Promethazine. PubChem. https://pubchem.ncbi.nlm.nih.gov/compound/Promethazine. Date Accessed November 2, 2026.

Promethazine. StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK544361/. Date Accessed November 2, 2026.