A model theory of release of ill-stocked drugs from spherical capsules was introduced on the basis of Fick's law of diffusion. Adopting some initial conditions containing some characteristic constants, we obtained formulae for the time-dependent concentration and applied the theory to dimenhydrinate for demonstration. The cumulative amount of Dramamine was pictorialized in terms of the characteristic constants, which is expected to help determine the shelf life. (C) 2007 Elsevier B.V. All rights reserved.