Guaifenesin: Drug Interactions, Side Effects & Overdose

Instructor: Megan Gilbert

Megan has a master's degree in nursing and is a board certified Women's Health Nurse Practitioner. Her area of clinical focus is the impact of infectious disease on pregnancy. She has experience teaching college allied health classes. She is also a certified EMT and holds a certificate of added qualification in electronic fetal monitoring.

Guaifenesin is a common medication used to treat chest congestion. This lesson discusses risks associated with its usage including possible drug interactions, known side effects, and potential for overdose.

Safely Treating the Common Cold?

Feeling sick and miserable with a nasty cough, Sarah drags herself to the local pharmacy where she finds an aisle filled with cough medications. Many contain guaifenesin. She wonders how safe this medication she's about to take is for her and her family. Guaifenesin found both by itself and in combination with other medication in many cold and cough remedies.

Guaifenesin is a commonly used cough medicine in the United States. It functions mainly as an expectorant making secretions thinner and easier for patients to remove from their airways. For the guaifenesin to function properly - and for Sarah to start feeling better as soon as possible - she needs to drink plenty of water while taking it.

Before keeping a medication in your home, you want to make sure it is safe.

Drug Interactions

First, we need to know if guaifenesin is safe with any other medications Sarah may be taking. Many individuals consume medications on a daily basis or sporadically to manage illness related complaints. Many young women are on contraceptives, whether it's the oral contraceptive pill, a patch, the Depo-Provera shot, or another method. Other people take heart medications, psychiatric medications, or diabetic medications. How does guaifenesin behave in these complicated pharmacologic settings?

The answer is - it presents no concerns. There are no known drug interactions between guaifenesin and any foods or medications currently on the market. Guaifenesin is an incredibly safe drug from a drug interaction risk perspective. Sarah can feel safe taking it as needed without being concerned that it may interact with other medications she may be on. She knows that she can always call her primary care provider to confirm that there are no interactions, though.

It's important to note - guaifenesin is often combined with other medications such as dextromethorphan and pseudoephedrine. These medications have many drug interactions and require much more care when using them in combination with other medications.

Side Effects

Guaifenesin is a generally well-tolerated medication. The main side effects, or reported complaints after taking a medication, are minor nausea and occasional vomiting, this is usually seen in higher doses. Patients who experience these side effects tend to report that they improve with long term usage. Sarah can avoid this side effect by having a small meal at the time she takes the medication.

Rarely more serious side effects have been reported, these include:

  1. Persistent GI upset
  2. Headache
  3. Dizziness
  4. Skin Rash
  5. Hives
  6. Serious allergic reactions - including anaphylaxis


An overdose is when a substance is taken in a quantity beyond the standard recommended dosage resulting in a dangerous, potentially fatal situation. Overdoses can occur from benign substances such as water, illicit drugs such as heroin, or common medications such as acetaminophen. Any possible overdose is a serious matter. Anyone suspected of overdosing on any medication should be promptly evaluated by a medical professional at the nearest emergency department.

Poison Control is available in the United States around the clock at: 1-800-222-1222 or by dialing 911

But what is the real risk of accidentally overdosing on guaifenesin if she didn't realize she took two medications both containing the same medication? As an adult, the risk of overdosing is low. Guaifenesin has a wide margin of safety and is well tolerated even at the upper limits of normal dosing. When in doubt, though, calling a poison control resource is never a bad idea.

Children are more likely to suffer from an accidental overdose as they are smaller and it's easier for them to reach a potentially dangerous dosage than it is for an adult. This is particularly true if they are able to consume a concentrated liquid form of the medication - as seen in children's cough syrups, or if they eat many doses of the medication believing it is candy.

To illustrate the risk:

A typical pediatric dosage is only 50mg but a typical single (maximum) adult dosage is 400mg. Therefore, if a child were able to consume even just three adult doses (400mg x 3doses = 1200mg) this would be equivalent to consuming 24 pediatric doses (1200mg/50mg per dose = 24 doses).

When Sarah has guaifenesin in her home, she will want to make sure that it was kept out of the reach of children and will make sure that it is kept in the original child-proof bottle it was sold in.

The most common signs of an overdose with this medication are nausea, vomiting, and stomach pain.

Lesson Summary

Guaifenesin is a common cough expectorant used to help individuals clear phlegm more efficiently. It is well tolerated and has an excellent safety profile. It has no known food or drug interactions; however, it is often found in formulations with other medications that can produce drug interactions.

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