The present invention relates to a complex that includes mequitazine, a cyclodextrin, and an interaction agent wherein the rate of solubilization in water of complexed mequitazine, measured for a 2 g/l mixture of mequitazine in water at 35.degree. C. after 15 minutes of stirring, is greater than 50% at pH 9. The present invention also relates to a method of preparing the aforementioned complex and a pharmaceutical composition of which the complex is a part.