Disclosed is an auto-injection apparatus for receiving a syringe, including: an outer casing enclosing a drive assembly and a syringe carrier configured to hold a barrel of the syringe, the syringe carrier being forward of the drive assembly and having stowed and delivery positions; an interlock extending between the syringe carrier and a syringe carrier housing at least partially surrounding the syringe carrier, the interlock preventing forward motion of the syringe carrier under the influence of an insertion actuator whilst in the stowed position. The drive assembly includes the insertion actuator for inserting a needle of the syringe into an injection site and a delivery actuator for driving a plunger into a barrel of the syringe which contains a substance for injection. The syringe carrier includes an interlock release mechanism which is configured to release the interlock such that the insertion actuator drives the syringe carrier forward.