4 Guaifenesin (Mucinex) Side Effects to Know About

Guaifenesin (Mucinex) is a popular over-the-counter (OTC) medication that treats cough. It’s available as immediate-release (IR) tablets or oral liquid and as extended-release (ER) tablets (guaifenesin ER). It’s also combined with other medications in several combination cough and cold products.

Guaifenesin is an expectorant. It helps loosen mucus in the chest and throat, so you can cough mucus up more easily. Guaifenesin is often used to treat a “wet cough,” which refers to a cough with mucus.

While many people don’t experience side effects from guaifenesin, they’re still possible. The likelihood of experiencing guaifenesin side effects may depend on your dosage and other individual factors.

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Guaifenesin side effects at a glance

Guaifenesin is well tolerated and has few side effects. If side effects do occur, they’re typically mild and resolve on their own. Examples include:

• Headaches

• Nausea

• Dizziness

• Diarrhea

Read on to learn more about these four possible guaifenesin side effects. We’ll also cover whether guaifenesin has an effect on sleep, mood, and more.

1. Headaches

Headaches are a common occurrence in adults. There are many possible causes, including various medications. While guaifenesin isn’t a medication that’s commonly known to cause headaches, it’s possible. However, headaches associated with guaifenesin are usually mild and go away on their own.

If you have a headache after taking guaifenesin, an OTC pain reliever like acetaminophen (Tylenol) or ibuprofen (Advil, Motrin) may help. However, if you took a guaifenesin product that contains one of these medications, make sure you’re not taking too much. For example, Mucinex Fast-Max Cold and Flu contains both guaifenesin and acetaminophen, so it may not be safe to take it with additional acetaminophen. Check with your pharmacist before taking OTC pain relievers if you’re taking a combination cough and cold product.

Keep in mind that since headaches can be caused by many things, it may be hard to tell if guaifenesin is the source of your symptoms. If you have headaches that don’t go away or get worse, let your healthcare professional know right away.

EXPERT PICKS: WHAT TO READ NEXT

• What’s the best over-the-counter cold medication? Our experts provide tips for finding the best over-the-counter cold or flu medication based on your symptoms.

• Does Mucinex work? While some people experience benefits, there’s not much evidence to show that Mucinex is effective for cold and flu symptoms.

• A sweet home remedy: Research shows that honey may help soothe a cough.

2. Nausea

Nausea is common with certain medications. While guaifenesin isn’t a medication that’s known for causing nausea, it’s possible. Taking guaifenesin with food (rather than on an empty stomach) may help. Staying hydrated, eating smaller meals throughout the day, and avoiding spicy or fried foods may also help eliminate other factors that contribute to nausea.

Keep in mind that other types of foods, another medication, or a health condition could be contributing to your nausea as well. If your nausea worsens or becomes severe, contact your healthcare professional. If you have a severe case of vomiting, which could mean vomiting that doesn’t stop or vomiting with severe abdominal pain, seek emergency care.

3. Dizziness

Dizziness is another possible guaifenesin side effect, but it’s not common. If you feel dizzy after taking guaifenesin, find a safe place to sit or lie down until the dizziness passes. And keep in mind that getting up too quickly from a sitting or lying position can worsen your symptoms. You should also avoid doing activities that require you to be alert, like driving, if you’re having frequent dizziness from taking guaifenesin.

Like the other side effects discussed here, there are many potential causes of dizziness. So there may be something else, aside from guaifenesin, that’s responsible for your symptoms. If your dizziness worsens or doesn’t go away, contact your healthcare professional for recommendations about what to do next.

4. Diarrhea

Some people experience diarrhea while taking guaifenesin. If this happens, drink enough fluids to avoid dehydration and stay away from foods that can worsen diarrhea, such as greasy or spicy foods and dairy products. If your diarrhea doesn’t seem to improve after a day or two, talk to your healthcare professional. They may want to discuss other potential causes for your diarrhea. They may also recommend trying an OTC antidiarrheal medication, like Imodium A-D (loperamide).

If you have diarrhea that’s accompanied by other symptoms, like a high fever or bloody stool, seek medical care immediately.

Does guaifenesin cause anxiety?

No, guaifenesin isn’t known to cause anxiety. However, other OTC cough and cold medications, such as the decongestant pseudoephedrine (Sudafed), can cause anxiety, restlessness, and nervousness. So if you take a medication like Mucinex D, which contains a combination of guaifenesin and pseudoephedrine, you may experience anxiety as a side effect.

Does guaifenesin make you sleepy? Or will guaifenesin keep you awake?

No, guaifenesin isn’t known to make you sleepy or keep you awake. But other OTC cough and cold medications may have these effects. For example, the antihistamine diphenhydramine (Benadryl) is known for causing drowsiness. And pseudoephedrine can make you feel more awake and restless. So if you’re taking guaifenesin as part of a combination cough and cold product, you might experience these effects.

Does guaifenesin increase blood pressure or heart rate?

No, guaifenesin doesn’t affect blood pressure or heart rate. So, typically, products that only contain guaifenesin as an active ingredient are considered safe for people with heart problems. 

Other OTC cough and cold medications may not be safe, though, depending on your medical history. For example, pseudoephedrine can increase blood pressure and heart rate. 

If you have a heart condition, check with your healthcare professional and pharmacist before taking a combination cough and cold product. They can let you know what products are safe for you.

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Written by:

Austin Ulrich, PharmD, BCACP

Austin Ulrich, PharmD, BCACP, is a board-certified ambulatory care clinical pharmacist. In his early career, he provided direct patient care in a variety of settings, including hospital and community pharmacies, and in a primary care clinic as a clinical pharmacist.

Edited by:

Amy B. Gragnolati, PharmD, BCPS

Amy Gragnolati, PharmD, BCPS, is a pharmacy editor for GoodRx. Amy currently holds her pharmacist license in Georgia and California.

Reviewed by:

Alex Brewer, PharmD, MBA

Alex Brewer, PharmD, MBA, is a licensed pharmacist specializing in chronic disease and health and wellness. Upon completing his residency, he worked in the managed care field, conducting medication therapy management and adherence counseling sessions with Medicaid, Medicare, and private insurance patients, before transitioning to a career in medical writing.

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