A self-sheathing injection assembly that includes a sheath protecting the medical professional from accidental punctures from the needle. The sheath is slidable to expose the end of the needle, and the sheath is lockable in the exposed condition with a detent mechanism. The separable needle assembly also includes features that firmly couples a carpule of medicine to the needle assembly, such that upon removal of the needle assembly after use the carpule remains attached to the needle for simultaneous disposal.
