The invention described herein provides a fast dispersing oral solid dosage form containing monoamine oxidase B inhibitor (MAO-B inhibitor) as the active ingredient, and method of treating disease therewith, such as Parkinson's disease. In one embodiment, the monoamine oxidase B inhibitor selegiline or its analogue can be the sole active ingredient in the composition administered. The dosage form composition is formulated to promote absorption through the buccal, sublingual, pharyngeal and/or esophageal mucous membrane tissue, such that at least 5% of the active ingredient is absorbed within one minute of placement in the oral cavity, as determined by a buccal absorption test. Monoamine oxidase B inhibitor compounds administered in accordance with the invention decrease the amount of undesirable metabolites associated with first pass effect of selegiline, for example, such as amphetamine and methamphetamine. The invention provides a number of other advantages over conventional orally administered tablet forms, including administration of monoamine oxidase B inhibitor compounds to patients that have difficulty swallowing.