A cough is a sudden and often repetitively occurring reflex that helps to clear the large breathing passages from secretions, irritants, foreign particles, and microbes.
It consists of three phases:
- an inhalation,
- a forced exhalation against a closed glottis, and
- a violent release of air from the lungs following opening of the glottis.

Coughing is either voluntary or involuntary.
Cough is a common, and at times distressing, symptom. Up to 40% of advanced cancer patients report cough, and while a smaller percentage find their cough distressing, severe cough can lead to dyspnea, nausea/vomiting, sleep impairment, chest and throat pain, and impaired communication.
Common etiologies of cough include infections of the upper and lower airway, asthma and COPD, lung cancer or lung metastases, interstitial pulmonary processes (such as lymphangitic tumor spread or pulmonary edema), gastroesophageal reflux, aspiration, and drugs. Common drug causes include ACE inhibitors, NSAIDs, and inhalant medications.
Evaluating for reversible causes is appropriate if consistent with the goals of care and prognosis. If possible, treatment should be directed at the underlying cause.
Many patients, however, will benefit from symptomatic therapy for a distressing cough while waiting for acute therapy to work, or have a chronic cough not amenable to treatment (e.g., cough due to advanced lung cancer).

Adapted from Marks S and Rosielle DA. Fast facts and concepts #199. Opioids for cough. Internet. January 21, 2016.