Robitussin DM can help reduce cough and loosen phlegm. It may interact with some medications, including those for certain psychiatric conditions.

Robitussin DM is a cough medicine for treating your cold or flu. Here’s what you need to know, including how it works, the forms it comes in, as well as side effects, interactions, and warnings.

Robitussin DM is used to temporarily relieve your cough from minor throat irritation or a cold. It also helps loosen phlegm from chest congestion so that you can cough it up and spit it out.

Robitussin DM comes in a liquid form that you take by mouth. It comes in regular-strength, maximum-strength, sugar-free, and children’s formulations.

Robitussin DM contains two active ingredients: dextromethorphan and guaifenesin.

Dextromethorphan is an antitussive drug used to help relieve constant coughing. It helps stop your cough by decreasing activity in your brain that triggers your impulse to cough. However, it doesn’t treat what triggers your coughing impulse in the first place, such as a cold or throat irritation.

Guaifenesin belongs to a class of drugs called expectorants. These drugs help loosen up and thin phlegm (mucus) in your throat and lungs so that your coughs are more productive. A productive cough will help bring up mucus that is causing chest congestion. This clears your airways, making it easier for you to breathe. Guaifenesin helps relieve chest congestion, but it doesn’t treat the cause of your congestion.

Robitussin DM Peak Cold Cough + Chest Congestion

12 years and older10 mL every four hours, and no more than 60 mL per day
younger than 12 years do not use

Children’s Robitussin DM Cough and Chest Congestion

12 years and older10-20 mL every four hours, and no more than 60 mL per day
6-11 years5-10 mL every four hours, and no more than 40 mL per day
younger than 6 yearsdo not use

Each active ingredient in Robitussin DM causes different side effects. These side effects can be more mild. However, some can be serious.

Mild side effects of dextromethorphan

The more mild side effects of dextromethorphan include:

  • dizziness
  • lightheadedness
  • drowsiness
  • nervousness
  • restlessness
  • nausea
  • vomiting
  • stomach pain

Side effects are usually not too common when you use Robitussin DM as recommended, but nausea is more common than the others. Taking Robitussin DM with food or milk may help ease nausea, vomiting, and upset stomach. If you have side effects and they become bothersome, stop taking Robitussin DM and ask your doctor or pharmacist to recommend another product.

Mild side effects of guaifenesin

The more mild side effects of guaifenesin include:

  • headache
  • nausea
  • vomiting

These side effects are usually rare. However, they’re more likely if you use more Robitussin DM than recommended. Only mild side effects are associated with guaifenesin. There are no serious side effects associated with it.

Serious side effect of dextromethorphan

A rash may be a serious side effect of dextromethorphan. It can indicate an allergic reaction. If you develop a rash while taking Robitussin DM, stop taking the medication and contact your doctor immediately.

The active ingredients in Robitussin DM can interact with other drugs, vitamins, or herbs you may be taking.

Drugs that can interact with dextromethorphan and guaifenesin include drugs from the monoamine oxidase inhibitor (MAOI) class. These drugs treat a variety of psychiatric conditions, including depression and Parkinson’s disease. They include:

  • isocarboxazid
  • phenelzine
  • rasagiline
  • selegiline
  • tranylcypromine

To help avoid interactions, be sure to tell your doctor about all the medications, vitamins, or herbs you’re taking. To find out how this drug might interact with something else you’re taking, talk to your doctor or pharmacist.

Robitussin DM is sometimes misused to experience a high known as “robo-tripping.” This misuse is very dangerous because it often leads to overdose. Dextromethorphan overdose can cause:

  • confusion
  • giddiness
  • slow breathing
  • nausea
  • vomiting
  • agitation
  • nervousness
  • restlessness
  • unsteadiness
  • dizziness
  • vision changes
  • shortness of breath
  • fast heart rate
  • hallucinations (seeing or hearing things that do not exist)
  • seizures
  • coma

In cases of overdose, call your local poison control center. If the overdose causes seizures or coma, call 911.

Talk to your doctor before using Robitussin DM if you’re pregnant, breastfeeding, or planning to do either. You may need to choose between breastfeeding and taking this medication. It’s also not known if the active ingredients in Robitussin DM could be harmful to your pregnancy. Your doctor may recommend lowered doses or other options for you.

Robitussin DM may be the drug to help ease your chest congestion and cough. However, some people may need adjusted dosages or other remedies for their coughs.

For example, dextromethorphan can increase the risk of drowsiness in older people. So, if you’re an older adult, you may need to use a lowered dose of Robitussin DM. Talk to your pharmacist or doctor to find out an appropriate dose.

Also, don’t use Robitussin DM for chest congestion that produces a large amount of phlegm. Excessive phlegm can be a sign of infection and should be treated with other medication. You also shouldn’t use Robitussin DM for coughs related to:

  • smoking
  • asthma
  • chronic bronchitis
  • emphysema

Talk to your doctor about other remedies for these types of coughs.