I smoked for a lon g time, then quite about 18 yrs ago.. I coughed like that for a month or so, cleaning the crud out of my lungs, then breathed great after the coughing stopped..
I agree with Devlyn, once the damage is done, it's pretty much permanent..
The worst is when I see these old folks with oxygen tubes and pulling a tank on wheels, and still stop off to have a siggy..