An additive adapter for use in conjunction with an injector wherein the injector includes a cylindrical body having a rearward open end and a forward end necked inwardly to form an annular lip. The forward end having a central opening of reduced diameter which is closed off by a sealing diaphragm. A plunger is sealingly and slidably fitted in the rearward portion of the body to form a medicament chamber between the sealing means and the plunger. A needle hub is affixed to the annular lip and carries a needle which is in fluid communication with the medicament chamber upon the opening of the sealing diaphragm. The additive adapter comprises a main body portion including a cylindrical skirt portion extending from the rearward end of the cylindrical sleeve. The skirt is sized to snugly engage and fit over the forward portion of the injector's cylindrical body. A cylindrical shield having a diameter larger than the cylindrical sleeve extends from the forward end thereof. A cap fits on and closes off the forward open end of the shield and a retaining assembly extends inwardly from the main body portion to engage the annular lip of the necked end of the injector body to retain the adapter in assembled condition on the aforesaid body.
