I am just wondering, is it possible to undo the effects of smoking?

Takes time: Smoking does considerable damage and this increases with the time smoked and the daily number of smoked cigarettes. When you stop, your body has to adjust its metabolism, clean out toxins and regroup. This takes time and it is years that statistics of the smoker match those of the never smoked group. This is a noble goal however; the sooner you stop, the better.