Filast 500 Tablet is used to prevent chronic obstructive pulmonary disease(COPD), group of lung disorders in which the flow of air to the lungs is blocked and chronic bronchitis. It works by opening the airways and makes breathing easier. Filast 500 Tablet can be taken with or without food, but take it at the same time every day to get the most benefit. The dose and how often you take it depends on what you are taking it for. Your doctor will decide how much you need to improve your symptoms. You should take this medicine for as long as it is prescribed for you. Do not miss even a single dose, if in any case, you missed a dose, take it as soon as you remember or better to skip the missed dose and continue with regular dosing. It does not prevent the already started breathing trouble or COPD, hence always carry your medical inhaler with you for an emergency. The most common side effects of this medicine include headache, weight loss, dizziness, insomnia, and back pain. If these bother you, or appear serious, let your doctor know. There may be ways of reducing or preventing them. To overcome dizziness, you must avoid driving and attention-seeking activity until you do not know how medicine affects you. If you experienced sudden weight loss, then regular weight monitoring is required. Before taking this medicine, let your doctor if you suffer from depression, or suicidal thoughts, or if you have HIV, multiple sclerosis. Your doctor should also know about all other medicines you are taking as many of these may make this medicine less effective or change the way it works. You must inform your doctor if you are pregnant or breastfeeding before treatment.