Foristal 2.5mg Lontabs is an antiallergic medication used in the treatment of various allergic conditions. It provides relief from allergic symptoms such as runny nose, sneezing, redness, swelling, itching and watery eyes. Foristal 2.5mg Lontabs may be taken with or without food. Take it exactly as per your doctor's advice. 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. In case, you have missed any doses, take the next dose as soon as you remember it. However, you should never take a double dose.Sleepiness is the most common side effect of this medicine. Avoid driving or attention-seeking activity. If these bother you or appear serious, let your doctor know. There may be ways of reducing or preventing them. In some cases, it may cause dryness of mouth. To prevent it, drink more water and maintain good oral hygiene.Before taking this medicine, let your doctor know if you have glaucoma or have any gastro-related issues or have asthma. Inform your doctor if you are pregnant, or breastfeeding. 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. Generally, it is advised to avoid alcohol while on treatment.