A safety syringe comprising a barrel having an opening at an end thereof and a bung positioned in the barrel and creating a volume between the opening and the bung. The safety syringe also comprises a handle portion secured to the barrel and a syringe plunger slidably engaged with the handle portion and moveable within the barrel on an inward stroke to drive the bung forwards within the barrel to cause a substance within the volume to be expelled from the opening. The safety syringe further comprises a rotation mechanism configured to rotate the syringe plunger within the barrel at a point during the inward stroke when the syringe plunger is in contact with the bung, such that a rotational force is applied to the barrel and a brake connected to the handle portion and configured to provide a frictional force to resist the rotational force applied to the barrel.本發明提供了一種安全注射器，這種安全注射器包含：針筒，針筒之一端具有開口；一筒塞，係位於針筒中，並且於開口與筒塞之間提供空間；手柄部，係固定於針筒上；注射器柱塞，注射器柱塞以可滑動之方式與手柄部相接合，並且在內向行程中注射器柱塞可於針筒內移動，藉以於針筒內向前驅動筒塞，進而從開口排出位於空間內之物質。這種安全注射器還包含：轉動機構，被配置成在注射器柱塞與筒塞相接觸時在內向行程之一處使針筒內之注射器柱塞進行轉動，進而向針筒施加轉動力；以及制動器，係連接至手柄部，並且制動器被配置成提供摩擦力，藉以抵抗施加於針筒之轉動力。
