Abstract The adsorption of a drug onto solid dosage form excipients may influence its dissolution characteristics, analytical testing and bioavailability. This is particularly important for drugs which are normally used in low doses such as ketotifen fumarate. Ketotifen fumarate, an orally active prophylactic agent used for the management of bronchial asthma and allergic disorders, was found to adsorb onto microcrystalline cellulose, croscarmellose sodium and pregelatinized starch. Croscarmellose exhibited the highest affinity followed by micorocrystalline cellulose and then pregelatinized starch. The Freundlich adsorption isotherm was found to best describe the adsorption data indicating that adsorption is a continuous function of the initial drug concentration. The extent of adsorption of ketotifen onto croscarmellose showed dependency on the pH of the media. In addition, a correlation between adsorption of the drug and its solubility at different pH values was observed. The low and negative values of the heat of adsorption (AH) of ketotifen obtained in case of croscarmellose sodium and the pH dependency in case of its adsorption onto microcrystalline cellulose suggest that the predominant mechanism of ketotifen adsorption is physical and exothermic in nature.