Is promethazine and cough syrup the same?

Quick Answer

Promethazine and cough syrup are not exactly the same thing. Promethazine is an antihistamine that is often added to cough syrups to help treat cold symptoms. However, promethazine is just one ingredient that may be found in some cough syrups. Cough syrups can contain a variety of active ingredients depending on the specific formulation. So while promethazine and cough syrup are related, they are not identical products.

What is Promethazine?

Promethazine is a first-generation antihistamine that is used to treat allergies, motion sickness, nausea and vomiting. It may also be used as a sedative or sleep aid. Some of the brand names for promethazine include Phenergan, Promethegan and Avomine.

Promethazine works by blocking the effects of histamine in the body. Histamine is a chemical that is released by the immune system during an allergic reaction. It causes many of the annoying symptoms of allergies, like itchy eyes, runny nose and sneezing. By blocking histamine, promethazine provides relief from these symptoms.

Promethazine also has some anticholinergic properties, meaning it blocks the action of acetylcholine. Acetylcholine is a neurotransmitter involved in the transmission of nerve impulses. One effect of anticholinergic drugs is drying up mucus secretions, which makes promethazine useful for treating runny noses or excess mucus production associated with colds and allergies.

The drowsiness associated with promethazine is due to its effects on the central nervous system. It interacts with various receptors in the brain that result in sedation and sleepiness. This makes it useful when treating cold and flu symptoms that may be disruptive to sleep.

Some key facts about promethazine:

  • First approved for medical use in the 1950s
  • Classified as a first-generation antihistamine
  • Sold under brand names like Phenergan and Promethegan
  • Used to treat allergies, motion sickness, nausea, vomiting
  • Causes drowsiness due to sedative effects
  • May be prescribed alone or combined with other medications
  • Available in oral tablet, rectal suppository, injectable solution
  • Considered safe and effective when used appropriately

What is Cough Syrup?

Cough syrups are oral medications that are used to treat coughs caused by colds, flu, allergies or other conditions. There are many different brands and formulations of cough syrup available both over-the-counter and by prescription.

Unlike promethazine, cough syrup is not a single active ingredient. Cough syrup is a blended liquid medication that combines various drug ingredients along with flavorings and preservatives. The active drugs found in cough syrup may include:

  • Expectorants – helps loosen mucus
  • Antitussives – suppress the cough reflex
  • Dextromethorphan (DXM) – cough suppressant
  • Guaifenesin – expectorant
  • Antihistamines – reduce congestion and allergic symptoms
  • Promethazine – antihistamine, sedative
  • Codeine, hydrocodone – narcotic cough suppressants

So while promethazine is an antihistamine that may be found in some cough syrups, it is not equivalent to cough syrup. Cough syrup is the blended liquid medication, not a single active drug.

Some key facts about cough syrup:

  • Contains a mixture of drugs and ingredients
  • Used to treat coughs from various causes
  • Typically contains expectorants, antitussives
  • May include antihistamines like promethazine
  • Available over-the-counter or by prescription
  • Dosage depends on age and active ingredients
  • Should be taken as directed on the label

Relationship Between Promethazine and Cough Syrup

Now that we’ve reviewed promethazine and cough syrup separately, how are they related?

The key connection is that promethazine is one of the antihistamine drugs that can be formulated into certain cough syrups. By including promethazine, these cough syrups gain the antihistamine effects of promethazine to help treat allergy-related coughs and colds.

Here are some examples of how promethazine may be incorporated into cough syrup preparations:

  • Phenergan with Codeine – cough syrup containing promethazine and codeine
  • Promethazine VC – combination of promethazine and phenylephrine (decongestant)
  • Promethazine DM – combination of promethazine and dextromethorphan (cough suppressant)

So in summary:

  • Promethazine is an antihistamine drug that can be used for allergies, nausea, sleep
  • Cough syrup is a blended medication containing various active ingredients
  • Promethazine is included in some cough syrups for its antihistamine effects
  • Promethazine cough syrups help treat allergy symptoms that may contribute to coughs

While promethazine has multiple uses on its own, one of its roles is as an additive to cough syrups. So the two products are related and overlapping, but not identical.

Key Differences Between Promethazine and Cough Syrup

Despite the connection between promethazine and some cough syrup preparations, there are some key differences between the two:

Drug composition

Promethazine Cough syrup
Single active drug ingredient Mixture of active and inactive ingredients

Promethazine consists of only the promethazine molecule, while cough syrups incorporate promethazine along with various other drugs, flavors, preservatives and thickeners.

Medical uses

Promethazine Cough syrup
Allergies, nausea, vomiting, sedation Cough suppression, mucus thinning

While promethazine has a range of uses, cough syrups are primarily used for coughs caused by colds, flu and allergies. Promethazine adds allergy symptom relief to cough syrup.


Promethazine Cough syrup
Available only by prescription Many formulations sold over-the-counter

Promethazine is only available with a doctor’s prescription, while many simple cough syrups can be purchased at pharmacies without a prescription. More complex cough syrups still require a prescription.

So in summary, while promethazine and some cough syrups are related and overlapping, they have distinct differences in their drug composition, medical uses and regulation. Promethazine is an ingredient in certain cough syrups, not interchangeable with cough syrup as a class of medication.

Risks and Side Effects

If you are taking either promethazine or a cough syrup preparation, it’s important to be aware of the potential side effects and risks.

Promethazine risks and side effects

  • Drowsiness
  • Dizziness
  • Dry mouth and throat
  • Constipation
  • Blurry vision
  • Confusion
  • Difficulty urinating
  • Shakiness or tremors
  • Depression
  • Severe allergic reaction (anaphylaxis)

Promethazine has significant sedative effects that can impair mental alertness and motor coordination. It should not be used if you need to operate vehicles or heavy machinery. Risks are higher with increased dosage.

Cough syrup side effects

Since cough syrup contains a blend of medications, the potential side effects depend on the specific ingredients:

  • Drowsiness (from antitussives, antihistamines)
  • Dizziness, nausea
  • Constipation (from cough suppressants)
  • Dry mouth (from antihistamines)
  • Headache
  • Vomiting

Overdose risks are also greater with combination cough syrups containing multiple active ingredients. Use care when giving cough syrup to children due to the potential for oversedation.

Promethazine and Codeine Cough Syrups

A specialized category of cough syrup contains both promethazine and codeine. The codeine acts as a narcotic cough suppressant, while the promethazine provides antihistamine effects. Examples include brands like Phenergan with Codeine.

These cough syrups provide more powerful cough relief, but they also carry higher risks:

  • Greater drowsiness and sedation
  • Impaired coordination and judgment
  • Constipation
  • Nausea and vomiting
  • Respiratory depression
  • Potential for addiction and abuse

Promethazine/codeine cough syrups should only be taken when recommended by a doctor. Use extreme caution when driving or operating heavy machinery. The medication should be kept secure and out of reach of children. Do not use with other drugs that cause drowsiness, including alcohol, marijuana or sedatives.

Which Drugs Interact with Promethazine and Cough Syrup?

Due to the sedative effects of promethazine and cough syrup, using them in combination with certain other drugs can be dangerous:

  • Alcohol – increases sedation and impairs functioning
  • Marijuana – enhances drowsiness and cognitive impairment
  • Opioid painkillers – high risk for overdose and respiratory depression
  • Sleeping pills – excessive sedation, difficult breathing
  • Antidepressants – increases side effects of both medications
  • Muscle relaxants – amplified sedative properties

Let your doctor know about any other medications, prescription or over-the-counter, that you are currently taking before using promethazine or cough syrup. Serious complications can occur with interacting drugs. Do not exceed the recommended dosing.


In summary, promethazine is an antihistamine drug that is included as an ingredient in some cough syrup preparations. It adds allergy and cold symptom relief. However, promethazine is not the same thing as cough syrup, which is a blend of various active ingredients. While related, promethazine and cough syrup have key differences in their drug composition, uses and regulation. Understanding these differences allows you to use each product safely and effectively as intended.

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