Spontaneous relaxation of an amorphous solid changes its properties with time as does its slow crystallization both resulting from slow molecular diffusion that decreases its free energy When the solid is a pharmaceutical, this occurrence decreases its solubility and hence bioavailability thus decreasing its effectiveness during storage Its stability against crystallization or "shelf-life" is currently modeled by calculating the relaxation time, tau(glass) by using the specific heat C-p and the enthalpy of melting data in the viscosity-configurational entropy relation We consider merits of such calculations and find that use of. (i) the excess C-p and its hyperbolic dependence on temperature, (ii) the enthalpy of melting and (iii) the fictive temperature is inconsistent with the glass relaxation phenomenology. and their use leads to overestimate of tau(glass) and thus to a longer than real shelf-life of an amorphous pharmaceutical We also argue that Taus: Is not the same as the characteristic time of spontaneous structural relaxation of a glass and would not determine the nucleation or crystal growth rate in it (C) 2010 Elsevier B V All rights reserved