What Is Promethazine DM?

Promethazine DM (dextromethorphan and promethazine) is a combination cough syrup that treats common cold and allergy symptoms. It has two active ingredients: Dextromethorphan and promethazine. 

Warning

Promethazine DM should not be used in children under two years of age due to the potential for causing very slow breathing, which can be fatal (i.e., fatal respiratory depression).

Dextromethorphan is a non-narcotic cough suppressant (antitussive) that stops coughs and doesn’t contain narcotics that can be addictive. Promethazine is an antihistamine that treats allergies.

Of the two active ingredients, scientists are still learning how dextromethorphan treats coughs. Dextromethorphan may treat coughs because it is structurally related to certain types of opioids, like codeine. Codeine and dextromethorphan likely stop coughs by decreasing activity in the area of the brain responsible for producing coughs. Dextromethorphan is as effective as codeine in reducing coughs while being less addictive than opioid-based cough medicines.

Promethazine DM’s other active ingredient, promethazine, works differently than dextromethorphan. Promethazine is an antihistamine and blocks histamine receptors. 

Promethazine DM is only available with a prescription in the United States.

What Is Promethazine DM Used For?

The Food and Drug Administration (FDA) approved Promethazine DM for the temporary relief of the following:

Drug Facts

Generic Name: Dextromethorphan and promethazine

  • CoughUpper respiratory symptoms associated with allergies or a cold

How to Take Promethazine DM

Promethazine DM is a medication that should only be taken under a healthcare provider’s direct guidance and recommendation. Although it is relatively safe, it is only available in the United States if you have a prescription. Only take Promethazine DM as directed by your healthcare provider. Generally, dosing will vary between every four to six hours by mouth, as needed, while you’re feeling sick. 

If you’ve been given this cough syrup for a cold, drink lots of fluids to help loosen the mucus in your lungs. 

Since this medication also contains dextromethorphan, it should not be taken if you take any medicines in the monoamine oxidase inhibitor (MAOI) drug class.

Storage

Promethazine DM should be stored away from light and in a cool, dry place (i.e., not your bathroom). Keep your medications out of the reach of children and pets, ideally locked in a cabinet or closet.

If you plan to travel with Promethazine DM, get familiar with your final destination’s regulations. Make a copy of your Promethazine DM prescription, and if possible, keep your medication in its original container from your pharmacy with your name on the label. Ask your pharmacist or healthcare provider if you have any questions about traveling with your medicine.

Discard all unused and expired drugs but do not pour them down the drain or toilet. Ask your pharmacist or medical provider about the best ways to dispose of this medicine. And check out drug take-back programs in your area.

What Are the Side Effects of Promethazine DM?

This is not a complete list of side effects, and others may occur. A healthcare provider can advise you on side effects. If you experience other effects, contact your pharmacist or healthcare provider. You may report side effects to the Food and Drug Administration (FDA) at fda.gov/medwatch or 800-FDA-1088.

How Long Does Promethazine DM Take to Work?

Promethazine DM generally takes around 30 minutes to start reducing cough symptoms. Talk with your healthcare provider if your symptoms don’t improve within seven days of starting treatment.

Common Side Effects

Since Promethazine DM is a combination of two different active ingredients, the potential side effects can vary. 

Possible side effects of dextromethorphan include:

  • Drowsiness
  • Dizziness
  • Nausea
  • Vomiting

Possible side effects of promethazine include:

  • DrowsinessDisorientationDizzinessNauseaVomiting

Severe Side Effects

Contact your healthcare provider immediately if you develop any signs of a severe reaction. Call 911 if your symptoms feel life-threatening.

Serious side effects and their symptoms include:

  • Difficulty breathingFast heart rateChanges in blood pressureBlurred vision or double visionSevere confusionSeizuresRashComa

Long-Term Side Effects

Promethazine DM is relatively well tolerated when used appropriately. Promethazine DM is a drug that has the potential for misuse, which can be deadly. 

Some long-term side effects, which can indicate inappropriate use, include:

  • Abnormal heart rhythmChanges in blood pressureDrynessHallucinationsSeizures

Dosage: How Much Promethazine DM Should I Take?

Modifications

The following modifications (changes) should be kept in mind when using Promethazine DM:

Report Side Effects

Promethazine DM may cause other side effects. Call your healthcare provider if you have any unusual problems while taking this medication.

If you experience a serious side effect, you or your provider may send a report to the FDA’s MedWatch Adverse Event Reporting Program or by phone (800-332-1088).

Additional Content Provided and Reviewed by IBM Micromedex

The dose of this medicine will be different for different people. Follow your healthcare provider’s orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your healthcare provider tells you to.

The amount of medicine you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

Do not use Promethazine DM in children under two years of age.

Severe allergic reaction: Avoid using Promethazine DM if you have a known allergy to it or its ingredients. Ask your pharmacist or healthcare provider for a complete list of the ingredients if you’re unsure.

Pregnancy: It is not known whether Promethazine DM can cause fetal harm. Promethazine DM should be given to a pregnant person only if needed. Discuss with your healthcare provider if you are or plan to become pregnant, and weigh the benefits and risks of taking Promethazine DM during your pregnancy.

Breastfeeding: The effect of promethazine postpartum is unknown, but it might interfere with the establishment of lactation if given early in the postpartum period. Dextromethorphan can make its way into breast milk. Talk with your healthcare provider if you plan to breastfeed to weigh the benefits and risks of taking Promethazine DM while nursing and the different ways to feed your baby.

Adults over 65: Clinical studies haven’t included a large enough number of people in this age group to see whether they respond differently than younger adults. A lower dose will likely be used to start.

Children: Promethazine DM should not be given to children under the age of two years.

Other modifications: Use dextromethorphan with caution in people who are sedated or have to stay lying down (in a supine position). Promethazine should be used cautiously in people with heart disease or who have impaired liver function.

Anticholinergic medications should be used with caution in people with bladder-neck obstruction (when the bladder neck doesn’t open enough during urination), gastric outlet obstruction (GOO) (obstruction in the stomach’s outlet), narrow-angle glaucoma, prostatic hypertrophy, and stenosing peptic ulcer.

The promethazine and dextromethorphan in Promethazine DM both undergo changes in the body via “CYP” liver enzymes (i.e., “cytochrome P” enzymes). Some people metabolize drugs differently. For example, they may have less of the enzyme CYP2D6 in their body. This means that any drug that impacts CYP2D6 enzymes might not be cleared as quickly. In this case, your healthcare provider may need to change the dose of your medicine to avoid any unwanted effects.

Missed Dose

It’s okay if you miss a dose of Promethazine DM. Almost everyone will occasionally miss a dose of medicine once in a while. What’s important is that you take it as soon as you remember. If it’s already close to your next scheduled dose, then skip the missed dose and take the following dose at your next scheduled dosing time. Don’t try to double up to make up for the missed dose.

Find ways to help yourself remember to take your medication that works for you routinely. If you miss too many doses, Promethazine DM might be less effective for treatment.

Overdose: What Happens If I Take Too Much Promethazine DM?

Since Promethazine DM has the potential to be inappropriately used, overdoses can happen and may be fatal. The criteria determining if someone is experiencing an overdose are mainly based on symptoms. 

A person that has overdosed may experience the following:

  • SeizuresConfusionDifficulty breathingSedationSudden death

If you experience these symptoms or see someone else experiencing them after taking Promethazine DM, it’s essential to contact a poison control center immediately. The sooner that overdose symptoms are treated, the less likely complications will occur.

Precautions

What Are Reasons I Shouldn’t Take Promethazine DM?

Avoid using Promethazine DM if you’re allergic to it or any of its ingredients. Ask your pharmacist or healthcare provider for a complete list of the ingredients if you’re unsure.

What Happens If I Overdose on Promethazine DM?

If you think you or someone else may have overdosed on Promethazine DM, call a healthcare provider or the Poison Control Center (800-222-1222).

You and your healthcare provider must check your progress at regular visits. This will allow your healthcare provider to see if your medicine is working properly and to decide if you should continue to use it.

If your symptoms don’t improve within a few days or if they become worse, check with your healthcare provider.

Don’t take other medicines unless they’ve been discussed with your healthcare provider. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal (e.g., St. John’s wort) or vitamin supplements. Tell your healthcare provider if you drink grapefruit juice.

Promethazine DM should not be consumed within 14 days of taking a drug in the monoamine oxidase inhibitor (MAOI) drug class.

Promethazine DM should not be used in people that are in a coma.

Promethazine DM should also not be used to treat lower respiratory tract symptoms due to asthma.

Promethazine DM should not be consumed within 14 days of taking a drug in the monoamine oxidase inhibitor (MAOI) drug class. MAOIs can be used for depression, mood disorders, or Parkinson’s syndrome.

Promethazine DM should not be used in people that are in a coma.

Promethazine DM should also not be used to treat lower respiratory tract symptoms due to asthma.

What Other Medications Interact With Promethazine DM?

Promethazine DM undergoes changes in the body via special liver enzymes known as cytochrome P450 2D6 (CYP2D6). Other medicines that impact how CYP2D6 works may also change how well Promethazine DM works. These medicines may decrease how well CYP2D6 enzymes can clear other medications from the body. 

CYP2D6 inhibitors increase the amount of drugs in the body and create possible side effects. Examples of CYP2D6 inhibitors are:

  • Wellbutrin (bupropion)Prozac (fluoxetine)Paxil (paroxetine)Lamisil (terbinafine)Quinidex (quinidine)

CYP2D6 inducers are medications that increase CYP2D6 enzymes’ drug-clearing ability. CYP2D6 inducers decrease the amount of certain drugs in the body. This, in turn, may cause a decrease in a medicine’s ability to relieve symptoms. Examples of CYP2D6 inducers are:

  • DexamethasoneRifadin (rifampin)

Promethazine DM also has other interactions that are unrelated to any enzyme. Promethazine DM can reduce the effectiveness of epinephrine. Consuming Promethazine DM with medications that make you drowsy may increase the risk for severe side effects such as difficulty breathing or sedation. 

Some examples of relevant medicines that can make you drowsy are:

  • Alcohol (ethanol)Xanax (alprazolam)Lunesta (eszopiclone)CodeineCogentin (benztropine)

Talk with your pharmacist or healthcare provider for more detailed information about medication interactions with Promethazine DM.

And be sure to talk with your healthcare provider about any other medicines you take or plan to take, including over-the-counter, nonprescription products, vitamins, herbs, or plant-based medicines.

What Medications Are Similar?

Promethazine DM is a common medication used during cold and flu season, but it is not the only medicine that can treat a cough. Examples of other cough medicines are:

  • Benzonatate
  • Delsym
  • Robitussin

This list includes drugs also prescribed for the targeted condition(s). It is NOT a list of medicines recommended to take with Promethazine DM. It would be best if you did not take some of these drugs together. For example, Robitussin and Promethazine DM should NOT be taken together; they both have the same active ingredient, and you could risk an overdose. Ask your pharmacist or a licensed healthcare provider if you have questions.

How Can I Stay Healthy While Taking Promethazine DM?

To stay healthy while you’re not feeling well, it is essential to take Promethazine DM, as directed by your healthcare provider. It may be difficult to take medications regularly at first, but to feel better, or for your child to feel better, this cough syrup must be taken regularly. 

Frequently Asked Questions

  • Can I travel with Promethazine DM?
  • Since Promethazine DM is a liquid, it must be able to fit within 3.4 ounces (100 milliliters (mL)) or less, carried in a quart-sized bag per Transportation Security Administration (TSA) requirements. If you forget your medicine at home and are traveling internationally, you might be able to purchase Promethazine DM at your destination, depending on local laws and rules. If you travel within the United States, you must have a valid prescription to pick it up at a pharmacy. If you cannot get more Promethazine DM, look for a medication with dextromethorphan. Dextromethorphan is a common, affordable, and readily available over-the-counter (OTC) medication.
  • How can I manage the side effects of Promethazine DM?
  • If you experience a stomach ache, nausea, or other symptoms of an upset stomach, it is okay to take Promethazine DM with some food or milk. You can reduce the risk of constipation with a healthy diet consisting of ample fiber and water.
  • How much does Promethazine DM cost? Is there a way I can get help paying for it?
  • In the United States, a bottle of Promethazine DM might cost around $12. If you cannot afford Promethazine DM, a cheaper option is a medication called dextromethorphan. Dextromethorphan is a common over-the-counter (OTC) medication that is readily available and affordable.

Since Promethazine DM is a liquid, it must be able to fit within 3.4 ounces (100 milliliters (mL)) or less, carried in a quart-sized bag per Transportation Security Administration (TSA) requirements. If you forget your medicine at home and are traveling internationally, you might be able to purchase Promethazine DM at your destination, depending on local laws and rules. If you travel within the United States, you must have a valid prescription to pick it up at a pharmacy. If you cannot get more Promethazine DM, look for a medication with dextromethorphan. Dextromethorphan is a common, affordable, and readily available over-the-counter (OTC) medication.

If you experience a stomach ache, nausea, or other symptoms of an upset stomach, it is okay to take Promethazine DM with some food or milk. You can reduce the risk of constipation with a healthy diet consisting of ample fiber and water.

In the United States, a bottle of Promethazine DM might cost around $12. If you cannot afford Promethazine DM, a cheaper option is a medication called dextromethorphan. Dextromethorphan is a common over-the-counter (OTC) medication that is readily available and affordable.

In addition to taking this medication, try to get lots of rest, stay hydrated, eat a healthy diet based on your individual needs, and consume adequate fiber.

Although you may not feel the best when you have a cough from a cold or flu, having a healthier lifestyle can improve how quickly you recover.

Medical Disclaimer

Verywell Health’s drug information is meant for educational purposes only and is not intended to replace medical advice, diagnosis, or treatment from a healthcare provider. Consult your healthcare provider before taking any new medication(s). IBM Watson Micromedex provides some of the drug content, as indicated on the page.