A vial adapter may include first and second sections each having first and second ends joined to form a collar having a central passage in which a neck of a vial may be disposed. Each collar section may have a hook formed at each end, the hooks joined to join the collar sections together. The first ends may have at least one tab depending therefrom and the second ends may have at least one indent formed therein, the tab disposed within the indent with the hooks joined to each other. In addition or instead, the collar may have an inner surface with a groove separating the collar into first and second regions on opposing axial sides of the groove. The first and second regions may be deformable axially into the groove when the collar is acted upon with the neck of the vial in the central passage.
