The invention relates to a method for using a medical syringe, in which method the medical syringe comprises a cylinder part with retaining lugs or a retaining flange and a needle, and a plunger part which is movable within the cylinder part by moving the plunger rod extending outside the cylinder part with respect to the cylinder part, and the method comprising moving the plunger part with respect to the cylinder part by at least one industrial robot either outwards for drawing liquid into the medical syringe or inwards for injecting the liquid out of the medical syringe. In the method according to the invention, the plunger part is gripped with a gripper configured to prevent the plunger part from turning with respect to the gripper. The invention also relates to an apparatus for using a medical syringe, and a method and an apparatus for dissolving a pharmaceutical substance in a liquid by utilizing the method according to the invention for using a medical syringe.