What are the Different Types of Guaifenesin Side Effects?

Constipation is one possible side effect of guaifenesin.
Guaifenesin is commonly used to relieve chest congestion by making mucus thinner.
The risk of kidney stones may be reduced by drinking plenty of water.
Guaifenesin side effects may include the development of kidney stones.
After a doctor consultation, guaifenesin should be safe for a pregnant woman to take.
A small percentage of people report experiencing side effects like drowsiness and dizziness while taking guaifenesin.
Nausea is one possible side effect of taking guaifenesin.
Adding pseudoephedrine or phenylephrine to guaifenesin may cause difficulty sleeping.
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  • Written By: Tricia Ellis-Christensen
  • Edited By: O. Wallace
  • Last Modified Date: 25 September 2015
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Guaifenesin, which is most often used as an expectorant to help clear mucus from the airways, isn’t associated with a high number of side effects. Many people take this medicine with few problems. The matter may become slightly more complicated because the drug is often mixed with other medications that can cause more adverse effects. Alone, guaifenesin side effects are relatively minimal or extremely rare.

The most common of the guaifenesin side effects is nausea or vomiting, and this is often improved or avoided if people take the medication with food. Most people won’t experience this side effect. Higher than recommended doses tends to increase risk of these gastrointestinal symptoms. Another adverse effect some people report is the sensation of a dry mouth. This may be alleviated by taking the medication with plenty of water, which is advised because it can help thin mucus secretions and increase expectorant action.

A relatively small percentage of people experience guaifenesin side effects like drowsiness or dizziness, but this percentage is very small. An even smaller percentage of users of this drug develop a rash from taking it. The most serious of the guaifenesin side effects, development of kidney stones, is extremely rare. Risk for this adverse effect can be lowered by drinking plenty of water while using the medication. The drug has additionally been shown to very occasionally result in an anaphylactic allergic reaction.


In addition to being well tolerated when taken alone, there appears to be few or no medications that negatively interact with guaifenesin. The medicine seems appropriate for use in most people. Those who are prone to kidney stones might avoid it, and the drug is only recommended in pregnancy if the benefit is clearly established. Little evidence exists of it being harmful to a pregnant mother or fetus.

Indications for use become more complex when people take this medication in a combination form. The drug is frequently combined with other drugs like pseudoephedrine, phenylephrine, dextromethorphan, and even codeine. The addition of these other medicines can change and increase the side effects people will experience.

Adding pseudoephedrine or phenylephrine can cause adverse effects like excitability, difficulty sleeping, low appetite and constipation, in addition to the expected but rare guaifenesin side effects already mentioned. Dextromethorphan adds the possibility of experiencing increased drowsiness or dizziness, excitation, mental dullness and respiratory depression. Drugs like codeine have a host of potential side effects such as drowsiness or sleepiness, increased nausea, and constipation. Some of these add-on medications do have more significant contraindications, and use of them combined with guaifenesin should be checked with a doctor or pharmacist, particularly if a person has any other medical conditions or is using other medications.


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