Abstract: An improved medication delivery device is a pen sized instrument that is powered by compressed inert gas. The needle-less injector device contains pre-filled and pre-measured medication dosages. The injector device has a pre-filled and self-contained compressed gas for providing pressure to inject the medication into the skin surface without the use of a needle. The injector device has a pressure sensitive deployment mechanism which insures proper seating of the injector face against the skin surface before medication delivery is accomplished. The needle-less injector device assures safe use by inexperienced operators (including children) under adverse conditions.