A SAFE MEDICAL-DRUG INJECTOR (1) WITH A COLLAPSABLE PLUNGER COMBINATION (14) THEREOF IS PROPOSED. THE INJECTOR (1) INCLUDES A HUB (11) CONNECTED WITH A NEEDLE (10), A HOLLOW BARREL (12), AND A COLLAPSABLE PLUNGER COMBINATION (14) INCLUDING A HOLLOW CANNULA (16) AND A RETRACTABLE PLUNGER (15) THAT IS TELESCOPED WITH THE HOLLOW CANNULA (16). AT LEAST A STRESS ADJUSTABLE NOTCH (151) IS FORMED AT THE CORE OF THE RETRACTABLE PLUNGER (15) OR IN AN UPPER EDGE OF THE HOLLOW CANNULA (16), AND AT LEAST ONE RAISED PORTION (150) IS FORMED ON AN OUTER LATERAL SIDE OF THE RETRACTABLE PLUNGER (15) NEAR THE STRESS ADJUSTABLE NOTCH (151) TO BE CORRESPONDINGLY EMBEDDED WITH AT LEAST A DEPRESSION (160) FORMED ON AN INNER LATERAL SIDE OF THE HOLLOW CANNULA (16). THE ENGAGEMENT BETWEEN THE RAISED PORTION (150) AND THE DEPRESSION (160) IS RELEASED TO MAKE THE RETRACTABLE PLUNGER (15) DRAWN BACK TO THE HOLLOW CANNULA (16) WHEN A FOLLOWING PRESS IS APPLIED ON THE HOLLOW CANNULA (16) AFTER THE SAFE MEDICAL-DRUG INJECTOR (1) COMPLETES AN INJECTION. FIG. 3
