Patent ID: 7674241

Claim:
A safe medical-drug injector comprising: a needle hub connecting a needle; a hollow barrel connected with the needle hub for guiding the needle hub to be drawn back to the hollow barrel after an injection is completed; and a collapsable plunger combination inserted into the hollow barrel, the collapsable plunger combination comprising a hollow cannula and a retractable plunger, the hollow cannula comprising a first telescoping part and the retractable plunger comprising a second telescoping part, the first telescoping part telescoping with the second telescoping part, there being at least one raised portion formed on an outside wall of the second telescoping part to be correspondingly embedded in at least one depression formed on an inside wall of the first telescoping part, the raised portion and the depression engaging to each other; wherein the hollow cannula is formed with at least one stress adjustable notch on the upper edge, and wherein the engagement between the raised portion and the depression is released to make the retractable plunger drawn back to the hollow cannula when the stress adjustable notch deforms due to a following press on the hollow cannula after an injection is completed, and thereby spare space of the hollow barrel for accommodating the needle hub.