In summary, we measured the onset and completion temperatures of α→β polymorphic transitions in 1-adamantyl-1-diamantyl ether. We determined that the transition temperature is 31 °C lower under thermo-mechanochemical reaction conditions than the corresponding DSC transition temperature. § § The introduction of defects by milling likely reduces the kinetic barrier for the polymorph transition. Our findings advance the fundamental understanding of polymorphic transitions of organic molecular crystals under thermo-mechanochemical conditions, with potential applications in polymorph screening. Furthermore, the ability to manipulate polymorphic transition temperatures might have commercial consequences, for example, in patent claims.