Tobacco smoking hinders the natural movement of the small hairs (cilia) that transport mucus from your lungs. When you stop smoking, the cilia reactivate. You may cough more than normal while your cilia heal and mucus is removed from your lungs. Coughing up tar is only possible if you smoke between meals or with chemicals added to cigarettes that cause tar to gel into solid particles. Smoking reduces the effectiveness of most medications, including asthma drugs. If you smoke, ask your doctor about ways to quit safely.