A module for an injection system to co-deliver at least two medicaments is disclosed where a primary delivery device containing a primary medicament accepts a module containing a single dose of a secondary medicament and where both medicaments are delivered through a hollow needle. The module does not require the user to manually engage a reservoir containing the secondary medicament. Instead, a biasing member automatically activates the reservoir when the needle guard is retracted. The needle guard prevents accidental needle sticks before and after an injection,and locks after dose delivery. Restraining features are present on the module to prevent the needle guard from moving relative to the device, in a trigger locked position.