I'm currently on a codeine-based cough medicine and it has an expectorant in it to help bring up any mucus when you do cough because none of these medications completely eliminate it.

I personally only take it at night because I cannot function on codeine, but even then I still have a productive cough during the night.

These medications aren't (shouldn't be) prescribed to people with mild/moderate coughs. They're for people who can't sleep at night and can't get rest to fight off the infection (I was sleeping less than four hours when I saw my doc). They're for people who are coughing to the point of vomiting and injury (also me). So, generally people who are doing more harm to their bodies by coughing than they are by not coughing.

Most codeine cough medicines also have an expectorant in them as well so when you do cough it does help you get stuff out. None of the prescription cough medicines completely eliminate coughing so you'll still be able to clear mucus from your respiratory system.

I'm on one right now because I've got a pretty severe case of bronchitis, but I only ever take it at night time because even a little bit of codeine gets me hella high, and even then it only mildly reduces my cough.