Provided are mixing syringes having two chambers defined by a pair of pistons located one above the other inside the syringe. Mixing of components separately stored in each of the two chambers occurs when a reversible valve occluding a bore in the distal piston near the discharge end is unseated by removing the retention sleeve and pressing the knob, and the proximal piston nearer the top of the syringe is moved axially toward the distal piston. Further movement of the proximal piston causes it to abut the distal piston resulting in the two pistons acting as one to dispel the now mixed components through the discharge end. Methods are provided for using the syringes for storage and mixing components discharging the components from the syringe such as by administering the components to a patient in need thereof through a needle when the components are a medicament product.
