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.
Just like dextromethorphan and diphenhydramine, codeine is little better than a placebo for the treatment of coughs. Even if it helps (very slightly!) to suppress your cough, it certainly doesn't address the underlying problem that is causing the symptom.
You might consider trying some of these solutions to provide temporary relief, especially if you are using them at night to help you sleep. It has been my experience that the most damaging aspect of a cough is its ability to interfere with your sleep. Once you aren't sleeping well your ability to recover from the infection will be impaired.
You might also consider a high-quality, low-sugar chocolate, as it has been found to be helpful for coughs. Also theobromine, a cocoa derivative, may be a more natural and effective treatment for coughs.
However, recurrent infections that cause coughing is a wakeup call that your immune system is probably impaired, as that was most likely the reason you acquired the infection that is causing the cough.
There are a number of strategies you can follow that will improve your immune system sufficiently so you won't acquire the infection in the first place. Here are some effective, drug-free protocols to boost your immune system.