A retractable needle is provided for a syringe comprising a barrel and a plunger that comprises a portion capable of engaging the retractable needle for retraction. The retractable needle comprises a cannula, a needle body having a plunger-engaging member, at least one aperture and an elongate portion which houses the cannula, the cannula comprising an end which is in fluid communication with the at least one aperture, wherein the at least one aperture is located between the plunger-engaging member and the elongate portion. The positioning of the at least one aperture distal to the plunger-engaging member maximizes the efficiency of fluid delivery.一種可縮回注射針,用於包括針筒和活塞之注射器,該活塞包含能卡掣該可縮回注射針卡掣以縮回該可縮回注射針之部分,該可縮回注射針包括插管、具有活塞卡掣元件之注射針體、至少一開孔以及用以容納至少一部份該插管的延伸部,該插管包含端部,其與該至少一開孔相連通,其中,該至少一開孔是位於該活塞卡掣元件和該延伸部之間。該至少一開孔的位置是遠至該活塞卡掣元件,使液體輸送的效率最大化。100‧‧‧可縮回注射器110‧‧‧針筒114‧‧‧活塞端115‧‧‧注射針端113‧‧‧項圈118‧‧‧內壁121‧‧‧保護套130‧‧‧釋放環200‧‧‧活塞210‧‧‧活塞元件211‧‧‧軸桿216‧‧‧密封卡掣元件217‧‧‧螺紋突部220‧‧‧活塞外環套225‧‧‧底部230‧‧‧控制件231‧‧‧銨鈕232‧‧‧臂部233‧‧‧軸270‧‧‧壓縮彈簧300‧‧‧針筒接合件330‧‧‧針筒卡掣部400‧‧‧注射針組件410‧‧‧插管411‧‧‧插管端420‧‧‧注射針體423‧‧‧活塞卡掣元件425‧‧‧孔430‧‧‧注射針密封件800‧‧‧活塞密封件810‧‧‧注射針卡掣元件820‧‧‧凹槽
