What Is Promethazine-DM Syrup Used for?


Promethazine-DM is a combination of the medications promethazine and dextromethorphan. This clear, yellowish-colored, slightly pineapple smelling liquid is sensitive to light and must be dispensed in a light-resistant container with a childproof cap. Promethazine-DM syrup is prescribed to temporarily relieve upper respiratory symptoms, such as a cough, caused by allergies or the common cold.


  • One teaspoon of promethazine-DM contains the active ingredients of 15 mg of dextromorphan hydrobromide, 6.25 mg of promethazine hydrochloride and 7 percent alcohol. The inactive ingredients are ascorbic acid, citric acid, D&C yellow #10, FD&C yellow #6, menthol, methylparaben, orange pineapple flavor, propylene glycol, propylparaben, purified water, saccharin sodium, sodium benzoate, sodium citrate and sucrose.


  • Promethazine acts as an antihistamine. It also is effective as an anti-emetic, meaning it can decrease the feeling of nausea. One of the brand names of promethazine is Phenergan, which is commonly prescribed to prevent motion sickness.

    As an antihistamine, which is the desired effect in this medication, it binds to receptors in the body thereby blocking histamine, which is a protein that induces changes in cells causing itching, sneezing and increased mucus production. Promethazine affects the body quickly, within 20 minutes of ingestion. The effects can last from 6 to 12 hours.


  • Dextromorphan is an anti-tussive agent, meaning that it liquefies thick mucus. In this way it acts as a cough suppressant because as the mucus thins the cough reflex is decreased. Dextromorphan is absorbed into the body quickly, so it begins to act within 30 minutes. It can help limit coughs for up to 6 hours.


  • Promethazine-DM syrup should only be prescribed to relieve the symptoms of upper respiratory infections. This includes symptoms of cough, runny nose, sneezing and itchy watery eyes caused by the common cold, flu, allergy or hay fever. It is not effective in treating asthma.

Side Effects

  • Promethazine-DM syrup can induce several side effects, drowsiness being the most pronounced. Promethazine is often prescribed as a mild sedative. In addition, patients may feel dizziness, dry mouth or fatigue.


  • Because this medication can cause drowsiness, do not consume alcohol while taking promethzine-DM syrup as it can enhance this side effect. This medication should not be given to children younger than 2 years because it can cause respiratory depression. That is a condition in which breathing is so low that it does not support adequate gas exchange.

    Do not drive or operate machinery while taking this medication. Do not take promethzine-DM if you are also taking a monoamine oxidase inhibitor (MAOI), which is commonly prescribed as an antidepressant.

    Patients with heart or liver conditions should consult a doctor before taking this medication. Pregnant women should consult their doctor as the effect of promethazine-DM on a fetus is not known.

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