A cartridge (10) for injecting a pharmaceutical solution includes at least one flexible small bag (18, 22) made of thin film walls, having a chamber (12, 14) containing a pharmaceutical substance (S, P, L) and having a head surface (37) being outwardly convex. A syringe (100) for injecting a pharmaceutical solution (S) includes a body (102) extended along a main axis (X), an accommodating space (120) to accommodate a cartridge (10), and a plunger (110) with a head (113) being dome-shaped and convex towards the space (120), preferably asymmetrical with respect to the main axis (X). An injection kit for injecting a pharmaceutical solution including a syringe (100) and at least one cartridge (100).