Theophylline is a medication primarily used to treat respiratory diseases such as asthma and chronic obstructive pulmonary disease (COPD). It works by relaxing the muscles around the airways, making it easier to breathe. Theophylline is classified as a bronchodilator and can help improve lung function. This drug is available in various forms, including tablets, capsules, and liquid. Theophylline levels in the blood need to be monitored, as too much can lead to side effects like nausea, insomnia, and increased heart rate. It is important for patients to follow their healthcare provider's instructions when using this medication.