Ketotifen fumarate (sold under the brand name Zaditor) is an H1-antihistamine available in two forms. In its ophthalmic form, it is used to treat allergic conjunctivitis, or the itchy red eyes caused by allergies. In its oral form, it is used to prevent asthma attacks. Side effects include drowsiness, weight gain, dry mouth, irritability, and increased nosebleeds.

Zaditor - Consumer information sheet provided by the U.S. Food and Drug Administration Center for Drug Evaluation and Research.
Zaditor - Official Pharmaceutical Website - Promotional information for consumers with a link to more detailed information for health professionals.