What are Phenergan Tablets?

October 7, 2025 •

4 min read

According to the Cleveland Clinic, the brand name medication Phenergan is generically known as promethazine, an antihistamine that prevents and treats symptoms of allergic reactions, motion sickness, and nausea. These versatile Phenergan tablets also possess sedative properties, making them a useful tool for presurgical relaxation.

Quick Summary

Promethazine, the active ingredient in Phenergan tablets, is a prescription medication with antihistamine and antiemetic properties. It is used to manage allergies, motion sickness, nausea, vomiting, and anxiety before medical procedures.

Key Points

Active Ingredient: Phenergan tablets contain promethazine, a prescription-only antihistamine and antiemetic.
Multi-purpose Medication: It is used to treat allergies, prevent motion sickness, control nausea and vomiting, and provide sedation for procedures.
Broad Mechanism of Action: It blocks histamine, dopamine, and acetylcholine receptors in the brain, contributing to its diverse therapeutic effects.
Significant Sedation Risk: A major side effect is marked drowsiness, which is enhanced by alcohol and other central nervous system depressants.
Safety Warning for Children: Phenergan should not be given to children under 2 years old due to the risk of serious, potentially fatal, respiratory depression.
Important Drug Interactions: It interacts with many medications, including opioids, antidepressants, and other sedatives, requiring careful consideration.
Photosensitivity Risk: The medication can increase skin sensitivity to sunlight, so patients should take precautions against sun exposure.

Understanding Phenergan Tablets

Phenergan is a brand name for the generic drug promethazine, a first-generation antihistamine and antiemetic that is available only by prescription. As a member of the phenothiazine class of drugs, it is known for its ability to cross the blood-brain barrier, which accounts for its significant sedative effects. This medication comes in several forms, including tablets, syrups, suppositories, and injections, but the tablets are one of the most common oral forms for treating various conditions.

How Phenergan Tablets Work

Phenergan's multifaceted effects are a result of its action on multiple neurochemical pathways. Its primary mechanism is blocking histamine H1 receptors, but it also interacts with other neurotransmitters.

Antihistamine Effects: By blocking histamine H1 receptors, Phenergan prevents or relieves the symptoms of allergic reactions. These symptoms include itching, sneezing, watery eyes, and hives that are triggered by the body's natural release of histamine.
Antiemetic Effects: Phenergan's ability to combat nausea and vomiting stems from its effect on the brain's chemoreceptor trigger zone (CTZ). It blocks dopamine receptors and, to a lesser extent, muscarinic receptors (part of the anticholinergic system), disrupting the signals that cause vomiting.
Sedative Effects: Its strong interaction with central nervous system (CNS) pathways makes Phenergan an effective sedative. It acts as a depressant on the CNS, promoting relaxation and sleepiness, which is useful for preoperative and nighttime sedation.
Anti-motion Sickness Effects: For motion sickness, promethazine reduces the sensitivity of the inner ear labyrinth, which plays a critical role in balance and the sensation of motion.

Common Uses for Promethazine Tablets

Phenergan tablets are prescribed for several conditions due to their broad range of effects.

Allergy Management: Relieves symptoms of hay fever (allergic rhinitis), allergic conjunctivitis, and other allergic reactions, including skin rashes and itching.
Motion Sickness Prevention: Can be used before travel to help prevent and control nausea, vomiting, and dizziness associated with motion.
Nausea and Vomiting Control: Used to treat nausea and vomiting caused by various factors, including surgery.
Sedation: Utilized to help patients relax and induce a quiet sleep before or after surgery.
Pain Adjunct: Can be used alongside other pain medications to help with sedation and enhance analgesic effects.

Administration and Safety Considerations

The proper administration of Phenergan tablets depends on the patient's age, weight, and the condition being treated. A healthcare provider will determine how the medication should be taken and the frequency. It is crucial to follow the prescription label and never take more than directed.

Important Safety Warnings

Do Not Use in Children Under 2: Phenergan carries a serious warning against its use in infants and children younger than two due to the risk of severe and potentially fatal respiratory depression (slowed or stopped breathing). Extreme caution is also advised when administering to children over two.
CNS Depression: Phenergan causes significant drowsiness. Patients should not drive or operate heavy machinery until they know how the medication affects them. This effect is amplified by alcohol or other CNS depressants.
Drug Interactions: Phenergan can interact dangerously with a wide range of medications, including alcohol, other antihistamines, antidepressants, sedatives, and opioids. Adjustment of other medications may be necessary.
Photosensitivity: The medication can make your skin more sensitive to sunlight, increasing the risk of sunburn. Protective clothing and sunscreen are recommended during sun exposure.

Phenergan vs. Other Anti-Nausea and Antihistamine Medications

Phenergan is often compared to other medications used for similar conditions. Its distinct mechanism of action and side effect profile set it apart from alternatives like Zofran and over-the-counter antihistamines. Below is a comparison table outlining key differences.


Feature	Phenergan (Promethazine)	Zofran (Ondansetron)	Dramamine (Dimenhydrinate)
Mechanism	Blocks histamine, dopamine, and acetylcholine receptors.	Blocks serotonin (5-HT3) receptors.	Blocks histamine (H1) and acetylcholine receptors.
Class	Antihistamine / Antiemetic (Phenothiazine).	Antiemetic (Serotonin antagonist).	Antihistamine / Anticholinergic.
Primary Uses	Allergies, motion sickness, nausea, sedation.	Chemotherapy-induced and post-operative nausea.	Motion sickness.
Availability	Prescription only.	Prescription only.	Over-the-counter (OTC).
Sedation	High risk of drowsiness.	Lower risk of drowsiness.	Moderate risk of drowsiness.
Side Effects	Drowsiness, dizziness, dry mouth, blurred vision.	Headache, fatigue, constipation.	Drowsiness, dizziness, dry mouth.
Pediatric Use	Contraindicated in children under 2.	Safe for use in children as young as 1 month (under strict supervision).	Safe for use in children over 2.

Conclusion

Phenergan tablets, containing the active ingredient promethazine, are a powerful and effective prescription medication for a range of conditions, including allergies, motion sickness, and nausea. Their broad mechanism of action, involving the blocking of several neurotransmitters, is responsible for both their therapeutic benefits and their notable sedative properties. While highly useful, especially for patients requiring sedation, their use comes with significant safety considerations, particularly the serious risks for very young children. Due to the potential for significant drowsiness and numerous drug interactions, patients should always follow their doctor's guidance carefully when taking Phenergan and avoid hazardous activities like driving. When considering treatment for nausea or allergies, comparing Phenergan with other medications is essential, as alternatives like Zofran or over-the-counter options may be more appropriate depending on the specific condition and patient safety profile. All individuals should discuss their full medical history and current medications with a healthcare provider before beginning treatment with Phenergan. For comprehensive information on Phenergan, consult the resources provided by official drug information websites or regulatory bodies.

Frequently Asked Questions

Phenergan is the brand name, and promethazine is the generic name for the same medication. Both contain the same active ingredient and are available by prescription.

The effects of Phenergan can begin relatively quickly, often within 20 minutes of taking an oral dose. The onset can vary depending on the specific condition being treated.

No, Phenergan can cause marked drowsiness, dizziness, and confusion that can impair your judgment and reaction time. You should not drive or operate machinery until you know how the medication affects you and can do so safely.

Phenergan is contraindicated for children under 2 years old due to the risk of fatal respiratory depression. Its use in children 2 years and older is at a doctor's discretion and requires caution.

Drinking alcohol while taking Phenergan can significantly increase the sedative effects, potentially causing dangerous levels of drowsiness, dizziness, and impaired coordination. Alcohol should be avoided entirely when using this medication.

Common side effects include drowsiness, dizziness, dry mouth, and blurred vision. If these are bothersome or persistent, you should speak with your healthcare provider.

Phenergan and Zofran work differently. Phenergan blocks histamine and dopamine receptors, while Zofran blocks serotonin receptors. Phenergan is generally more sedating than Zofran and has a broader range of uses beyond just nausea, including allergies and sedation.