Theophylline is a long-term control medicine. This means it is used daily to maintain control of your lung disease. It is not one of the first medications used for long-term control of lung diseases. There are safer and more effective medicines available. For people with chronic lung disease theophylline may be added to other medicines to improve symptoms and lung function. Theophylline relaxes the muscles around the airways in the lungs so air can flow more easily into the lungs.