What is Guaifenesin? Uses, warnings & side effects

Updated May 14, 2025  •  Published Dec 30, 2020

Guaifenesin (pronounced “gwai-feh-nuh-sun”) is an expectorant that is nearly universally found in over-the-counter cold, flu, cough, and other combination medications. People less commonly buy guaifenesin by itself, but standalone guaifenesin can be found on store shelves labeled as “mucus relief,” “mucus relief ER,” or “chest congestion.” These products are likely extended-release versions of guaifenesin that conveniently require only one dose to be taken every twelve hours. Extended-release guaifenesin is too strong for children younger than 12. Use immediate-release guaifenesin tablets or liquid instead.

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Guaifenesin overview

BRAND NAMES:

  • Mucinex, Contac Chest Congestion, Air-Power

Generic Names:

  • Guaifenesin

Uses:

  • Thins mucus so you can clear it from your head, throat, and lungs

Therapeutic Classes:

  • Expectorant

Forms:

  • Tablet, extended-release tablet, oral solution (liquid)

How it’s taken:

  • By mouth

What is Guaifenesin used for?

Guaifenesin relieves chest congestion by thinning mucus in the lungs.

What form(s) does Guaifenesin come in?

  • Tablet

    • 200 mg

    • 400 mg

  • Extended-release tablet

    • 600 mg

    • 1,200 mg

  • Liquid

    • 100 mg/5 mL

What are common Guaifenesin dosages?

  • For chest congestion:

    • In adults and children 12 years of age and older: 200–400 mg immediate-release guaifenesin (tablets or 2–4 teaspoons oral solution) every 4 hours OR 600–1,200 mg extended-release tablets every 12 hours 

    • In children 6–11 years of age and older: 100–200 mg immediate-release guaifenesin (½–1, 200 mg tablet OR 1–2 teaspoons oral solution) every 4 hours

    • In children 2–5 years of age and older: 50–100 mg immediate-release guaifenesin (½–1 teaspoon oral solution) every 4 hours

Find more detailed information about guaifenesin dosage, forms, and strengths here.

Guaifenesin images - What does Guaifenesin look like?

  • guaiFENesin
    100 tablets bottle

  • guaiFENesin
    20 tablets bottle

  • guaiFENesin
    30 tablets bottle

  • guaiFENesin
    473ml of 100mg/5ml bottle

  • guaiFENesin
    500 tablets bottle

  • guaiFENesin
    60 tablets bottle

  • guaiFENesin
    400mg tablet

How to take Guaifenesin

  • Follow the instructions on the medication label. Do not take more than directed or exceed the maximum daily dosage.

  • How to take guaifenesin tablets:

    • Take the tablet with a full glass of water.

    • Swallow the tablet whole. Do not crush, chew, or break the tablet.

    • Store guaifenesin tablets at room temperature. 

  • How to take guaifenesin oral solution:

    • Liquid or syrup guaifenesin products include a measured dosing cup, so measure each dose with the dosing cup.

    • You can also measure doses using measuring spoons. Most guaifenesin labels give dosing instructions in teaspoons (1 teaspoon = 100 mg).

    • The entire dose should be swallowed.

    • Store guaifenesin liquid at room temperature.

  • To help guaifenesin loosen mucus in the lung’s airways, drink extra fluids throughout the day and use a humidifier or steam vaporizer to keep the air moist.

What to do if you miss a dose of Guaifenesin

  • Take a missed dose when remembered.

  • If you take a missed dose, take the next dose at least four hours later (for immediate-release guaifenesin) or 12 hours later (for extended-release guaifenesin).

  • Do not take an extra dose to make up for a missed dose.

Guaifenesin contraindications - Who shouldn't take Guaifenesin?

  • You should not use this medicine if you have ever had an allergic reaction to guaifenesin.

Guaifenesin warnings

  • Tell any healthcare provider who treats you that you are using this medicine.

  • If pregnant or breastfeeding, consult with a healthcare provider before using guaifenesin. 

  • Before using guaifenesin, talk to a healthcare provider if you have:

    • A cough with too much phlegm

    • A chronic cough due to smoking, asthma, emphysema, or bronchitis

  • Guaifenesin is a common ingredient in many non-prescription combination drugs (like cold or flu medications). To avoid an accidental overdose, always check the ingredients of combination medications before taking guaifenesin or any other OTC medication.

  • Chest congestion and coughing may be symptoms of a more serious or chronic illness. If phlegm and coughing persist for longer than seven days or there are other symptoms, such as rash or fever, see a healthcare provider. 

  • Some guaifenesin liquids contain aspartame, which may cause a serious reaction in people with phenylketonuria.

Guaifenesin interactions & what to avoid when taking Guaifenesin

Guaifenesin side effects - How does Guaifenesin make you feel?

  • Nausea

  • Vomiting

  • Headache

  • Diarrhea

  • Rash

  • Drowsiness

Sources:

Guaifenesin News & Research

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