Histan is a 4mg antihistamine medication containing chlorpheniramine maleate, used to treat allergy symptoms like sneezing, runny nose, and itchy/watery eyes. Each pack contains 20 tablets divided into 2 blister strips of 10 tablets each. This medication should be taken as directed by your healthcare provider. For adults and children over 12 years, the typical dose is 4mg every 4-6 hours, not exceeding 24mg in 24 hours. Common side effects may include drowsiness. Do not take if you are allergic to chlorpheniramine or have certain medical conditions. Consult your doctor before use if pregnant, breastfeeding, or taking other medications. Store at room temperature away from moisture and heat.