Guaifenesin is an expectorant. It helps loosen congestion in your chest and throat, making it easier to cough out through your mouth.

Theophylline is a bronchodilator. Theophylline works in several ways: It relaxes muscles in your lungs and chest to increase airflow, decreases the sensitivity of your lungs to allergens and other substances that cause inflammation, and increases the contractions of your diaphragm so that more air is drawn into the lungs.

The combination of guaifenesin and theophylline is used to treat symptoms of asthma, bronchitis, and emphysema.

Guaifenesin and theophylline may also be used for other purposes not listed in this medication guide.

Call your doctor right away if you experience nausea, vomiting, insomnia, restlessness, seizures, an increased heart rate, or a headache. These symptoms could be signs of too much theophylline in your blood.

Do not start or stop smoking without first talking to your doctor. Smoking changes the way your body uses theophylline, and you may need a dose adjustment.

Do not take more of this medicine than is prescribed without consulting your doctor. Seek medical attention if you are having increasingly difficult breathing.

You should not take this medication if you are allergic to guaifenesin or theophylline, or if you have:

• a stomach ulcer; or

• epilepsy or another seizure disorder.

Before taking guaifenesin and theophylline, tell your doctor if you are allergic to any drugs, or if you have:

• heart disease or high blood pressure;

• a heart rhythm disorder;

• congestive heart failure;

• fluid in your lungs;

• a thyroid disorder;

• fever;

• liver disease; or

• kidney disease.

If you have any of these conditions, you may need a dose adjustment or special tests to safely take this medication.

FDA pregnancy category C. This medication may be harmful to an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant during treatment.

Guaifenesin and theophylline can pass into breast milk and may harm a nursing baby. Do not use this medication without telling your doctor if you are breast-feeding a baby.

Older adults may be more likely to have side effects from this medication.