Taking Codiene For Relief From Cough After Being Diagnosed By Lung Cancer. When Should I Take Codeine?

My mum has lung cancer, just diagnosed in the last two weeks. She has just started taking codiene to give her some relief from the cough. After talking to several nurses and doctors, we are confused as to where the mucus goes when she takes the codiene. Some say that most of the mucus is reabsorbed into the body. Others have said that if it is not coughed up it could or will build up and cause pheumonia. Just wanted to clarlfy this. Also, when is the best time to take the codiene at night. Mum s worried about when to take it, was told take an hour before and the most recent strength it just says at night. She s not taking my advice that it s a matter of trial and error, what works best for her.