Theophylline is widely used in the treatment of respiratory conditions such as asthma and chronic obstructive pulmonary disease (COPD). It works by relaxing the muscles in the airways and reducing the sensitivity of the lungs to allergens and irritants, which helps improve breathing. Additionally, it is sometimes prescribed to manage symptoms of apnea in premature infants, aiding in the stimulation of their respiratory system. Theophylline also has mild diuretic effects, which can be beneficial in certain medical conditions. However, its use requires careful monitoring due to its narrow therapeutic index and potential side effects.