Codeine, which is a common ingredient in cough medicines, proved to be barely more effective than a placebo when used in the treatment of coughing resulting from chronic lung disease.
Researchers triggered coughing in test subjects with chronic obstructive pulmonary disease (COPD), then gave them treatment and monitored their coughing for 10 hours.
Patients who were given a placebo had their rate of coughing drop from 8.27 seconds per hour to 7.22 seconds per hour. Those given codeine only had their coughing drop slightly further, to 6.41 seconds per hour.