Clemastine Fumarate Syrup Antihistamine Oral Solution 0.5mg/5 mL, 120 mL (RX)Clemastine fumarate is an antihistamine medication primarily used to relieve symptoms of allergies, such as sneezing, runny nose, and watery eyes. Clemastine fumarate is also prescribed for the treatment of itching due to allergic skin reactions, insect bites, or hives. Clemastine fumarate may also be used to relieve symptoms of allergic asthma and as a sedative for insomnia. In some cases, it may be used to treat symptoms of the common cold or flu.