Introduction

The scene: You have chest congestion, so you cough and cough but still get no relief. Now, on top of the congestion, you also can’t stop coughing. You consider Mucinex DM because it’s made to treat both congestion and constant coughing. But before you use it, you want to know about the side effects.

Here’s a look at the active ingredients of this drug and the side effects they can cause. Keep reading to find out when the effects are most likely to happen, how to ease them, and what to do in the rare case that they’re severe.

What does Mucinex DM do?

Mucinex DM is an over-the-counter medication. It comes in an oral tablet and an oral liquid. It has two active ingredients: guaifenesin and dextromethorphan.

Guaifenesin helps loosen mucus and thin the secretions in your lungs. This effect helps make your cough more productive by allowing you to cough up and get rid of bothersome mucus.

Dextromethorphan helps relieve the intensity of your cough. It also decreases your urge to cough. This ingredient is particularly helpful if you have trouble sleeping because of coughing.

Mucinex DM comes in two strengths. Regular Mucinex DM comes as an oral tablet only. Maximum Strength Mucinex DM is available as an oral tablet and oral liquid. Most people can tolerate both Mucinex DM and Maximum Strength Mucinex DM at the recommended dosage. Still, there are some side effects that can happen when you take either strength of this drug.

Mucinex DM side effects

Digestive system effects

Side effects of this drug can affect your digestive system. These effects are not common when you use the recommended dosage. However, if they do happen, they can include:

  • nausea
  • vomiting
  • constipation

stomach pain

Nervous system effects

To help control your urge to cough, this drug works on receptors in your brain. In some people, this may also cause side effects. Side effects at the recommended dosage are uncommon but may include:

  • dizziness
  • drowsiness
  • headache

These side effects are rare. If you have these side effects and they are severe or don’t go away, contact your doctor.

Skin effects

Side effects on your skin are uncommon at a normal dosage, but may include an allergic reaction. This reaction typically causes a rash on your skin. If you have a skin rash after using Mucinex DM, stop using the drug and contact your doctor.

If the rash gets worse or if you notice swelling of your tongue or lips, or have any difficulties breathing, call 911 or local emergency services immediately. These may be signs of a severe allergic reaction.

Side effects from overuse

Side effects of Mucinex DM are most likely to happen if you use too much of this drug. That’s why you should only use it as recommended. Side effects from overuse are also more severe. They can include:

  • breathing problems
  • confusion
  • feeling jittery, restless, or agitated
  • extreme drowsiness
  • hallucinations
  • irritability
  • seizures
  • severe nausea
  • severe vomiting
  • kidney stones

Symptoms of kidney stones can include:

  • fever
  • chills
  • vomiting
  • severe, persisting pain in your back or side
  • burning pain during urination
  • foul-smelling urine
  • cloudy urine
  • blood in your urine

Stop taking this drug and contact your doctor immediately if you experience any of these severe side effects.

Drug interactions and serotonin syndrome

If you take certain drugs for depression or Parkinson’s disease, called monoamine oxidase inhibitors (MAOIs), do not take Mucinex DM. Taking Mucinex DM while you take MAOIs can lead to a severe reaction called serotonin syndrome. Serotonin syndrome affects your heart and blood vessels. It’s a life-threatening reaction.

Learn more: Serotonin syndrome symptoms, causes, treatments, and more »

MAOIs include:

Other drugs that can increase your serotonin levels and lead to serotonin syndrome if you take Mucinex DM include drugs that treat depression, anxiety, and obsessive-compulsive disorder, such as:

Talk to your doctor before using Mucinex DM if you currently take any of these drugs.

Talk with your doctor

If you use Mucinex DM as directed, you will most likely experience only mild side effects, if you experience side effects at all. Most severe side effects of Mucinex DM come from overuse and misuse of this drug. If you have any doubts about taking this drug, talk to your doctor. Checking with your doctor for side effects is especially important if you take other drugs or have other conditions.