Ketotifen has anti-allergic properties and has been used similarly, to sodium chromoglycate in the prophylactic treatment of asthma. It also has the properties of an antihistamine. Ketotifen possesses marked anti-anaphylactic properties and is effective in preventing an asthmatic attacks. Ketotifen exerts as sustained inhibitory effect on histamine reactions, which can be clearly dissociated from its anti-anaphylactic properties. Experimental investigations in asthmatic subjects have shown that Ketotifen is as effective orally as a selective mast cell stabilizer administered by inhalation. Antihistamines were ineffective in those tests. The effectiveness of Ketotifen has been studied in long-term clinical trials. Asthma attacks were reduced in number, severity and duration and in some cases, the patients were completely freed from attacks. Progressive reduction of corticosteroids and/or bronchodilators was also possible. The prophylactic activity of Ketotifen may take several weeks to become fully established. Ketotifen will not abort established attacks of asthma.