Guaifenesin (Oral)


Guaifenesin is a drug used to treat phlegm, the clear mucus from the chest that you get when you have congestion from the flu or a cold. It works by thinning the phlegm or mucus in the lungs. This medication is available both via your doctor's prescription and as an over the counter medication available for your own purchase.

Don't give any over the counter cold and cough medicines to a child under four years old. This is due to the risk of serious or life-threatening side effects occurring.

Conditions Treated

  • Cold symptoms

Type Of Medicine

  • Oral tablet

Side Effects

Alongside reducing chest congestion from various infections, colds and allergies, the consumption of this drug can also produce some unwanted side effects. Not all of these side effects may be present at the one time; however, if you find they do occur, then you may be required to seek medical advice.

Some side effects of guaifenesin that occur aren't severe and don't require any urgent medical attention. You may find that these side effects begin to reduce or disappear altogether as time passes and your body begins to adjust to the medication. However, if any of the following side effects become bothersome or persistent, then you can seek advice from a doctor or local pharmacist for tips on ways to reduce or prevent these side effects altogether.

Directly below is a list of side effects that you should seek advice from your doctor or healthcare professional about if you start to experience them:

Less common or rare

You may experience other side effects that are not listed above. This is normal, but if you are concerned or worried, you should seek medical advice from a healthcare professional, especially if you notice anything unusual. All side effects can be reported to the FDA.


The final dose requirements for any drug are based on a number of individual factors. These include things such as your weight, age and height, any other medications you are currently taking, any other medical conditions you suffer from and what specific illness you are being treated for. Your reaction to the first dose will also be an indicator for your final dose.

You should keep to the dose that your doctor has specifically given you. Do not stop, change or alter your dose without prior consultation with a healthcare professional or doctor. If you take too much of your mediation, you could increase your risk of side effects, and if you take too little, you will reduce the effectiveness of the drug in treatment.

For regular oral dosage forms (an oral solution, capsules, tablets or syrup):


  • 200 to 400 milligrams every four hours.
  • Children six to twelve years old: 100 to 200 mg every four hours.
  • Children four to six years of age: 50 to 100 mg every four hours.
  • Infants and children up to four years of age: this drug should not be used in children under four years old.
  • For long-acting oral dosage forms (tablets or extended-release capsules):


  •  600 to 1200 mg every 12 hours.
  • Children six to twelve years of age: 600 mg every 12 hours.
  • Children four to six years of age: 300 mg every 12 hours.
  • Infants and children up to four years of age: this drug should not be used in children who are younger than four years old.
  • Proper use

You should drink plenty of water whilst taking this drug, as it will help loosen the phlegm or music in the lungs.

For those who take the extended-release type of this medication:

Swallow the full capsule, or, alternatively, open the capsule and place the medication on foods that are soft, such as jelly, applesauce, or soft cake, then swallow, but do not chew or crush the tablet.

For those who consume the extended-release type of this medication:

If the tablet has a groove within it, you can carefully break it into two pieces along the groove. Next, swallow the piece whole without chewing or crushing it.

If your tablet doesn't have a groove, it should be swallowed whole. Do not crush, break or chew the tablet before swallowing.

Don't worry if you miss a dose of your medication; you should take it as soon as you remember. The exception to this is if it's almost time for your next scheduled dose. You should skip the dose you have missed and revert back to your original dosing schedule. Under no circumstances should you double doses to make up for a missed dose.

If your symptoms do not improve, you should seek advice from your doctor.


It is possible that this drug can interact with other drugs that you are currently taking. These interactions can lead to severe side effects and reduce the effectiveness of each drug. To help limit this, it's important that your doctor knows about any and all the drugs you are currently taking. This should include any prescription and non-prescription drugs, as well as any vitamin supplements and herbal products.

In most cases, your doctor will try and avoid any interactions occurring, but in some cases, it may be unavoidable. It's best to also inform your doctor of any other medical conditions that you currently suffer from, as these can increase your risk of interactions, too.

There are currently no significant medications or medical conditions that interact severely with this drug. However, it is still a good idea to let your doctor know of all the current and past medications you have taken, in case a rare interaction occurs.



You should inform your doctor or healthcare professional of any allergies or unusual reactions you have suffered to this drug before, as you may be unable to use it. You should also make them aware of any other allergies you suffer from, including to animals, foods, dyes and preservatives.

Pediatric population

Although there is no specific information that compares the use of guaifenesin in children with its use in other age groups, this medication is not expected to cause any extra problems or side effects in children compared to adults.

However, you should still consult with your doctor before giving this medication to children suffering from a chronic cough, such as that which occurs with asthma, or to children who have an unusually large amount of phlegm or mucus with a cough. You may find that children who suffer from these conditions require a different type of medication for treatment.

This drug should not be given to children and infants younger than two years of age, unless you have been specifically told to do so by your doctor. Do not give any over the counter cold and cough medications to a child under four years old or to a baby. The use of these medications could cause serious and life-threatening side effects.

Geriatric population

Studies have not been conducted specifically on the older population with regards to this medication. As such, it's unknown whether they will work in the same way as they do for younger adults. Despite the fact that there is no specific information that compares the use of this drug in the elderly to other ages, this medication is not expected to cause any variation in problems or side effects in older patients.

Use in pregnancy and when breastfeeding

This drug is classified under FDA pregnancy category C. It is currently unknown whether guaifenesin can harm an unborn infant. You should let your doctor know if you are pregnant or intend to become pregnant whilst using this drug. It is also unknown if this medication can be transferred into breast milk and harm a nursing infant. It's best not to use this medication when breastfeeding a child without speaking to your doctor first.

If your cough hasn't improved after seven days or if you have a skin rash, fever or continuing headache, or a sore throat in combination with a cough, you should seek advice from your doctor. These signs could indicate that you are suffering from other medical problems.


The medication should be stored in a closed container and kept away from moisture, heat and light at room temperature. Prevent this medication from freezing. Keep this drug out of the reach of children.

Do not keep medication that has passed its expiry date or you no longer require. You should contact your local pharmacist for advice on the best way to dispose of medication you no longer require.


When used correctly, guaifenesin is successful in the treatment of chest congestion caused by allergies, the common cold and infections, such as the flu. This drug will not eliminate coughing altogether, however. Coughing is an important process, as it is the body's method to remove any excess mucus.

Do not operate machinery, drive or perform other hazardous activities until you know how your body will react to this drug. Some effects of guaifenesin will be noticed within thirty minutes after consumed orally; however, up to two days of regular doses may be required before you will experience the full effects of this drug. Delayed-release tablets can last up to twelve hours and liquid guaifenesin lasts on average of four to six hours.

You should let your doctor know if you are pregnant or intending on breastfeeding whilst using this medication. You should not give this drug, or any other over the counter drugs to treat coughs and flu, to children under the age of four. To do so could increase their risk of experiencing serious and life-threatening side effects.

If your symptoms do not improve, you should seek advice from your doctor, as you may have another underlying issue. If you require any further information about the practical uses of this drug, or you have any questions, you should contact your doctor or healthcare professional for advice.