A medicated module (4) for an injection system to co-deliver at least two medicaments is disclosed where a primary delivery device containing a primary medicament accepts a medicated module (4) containing a single dose of a secondary medicament (2) and where both medicaments are delivered through a single hollow needle (5). The medicated module (4) is user selectable so that it will deliver both the primary (1) and secondary medicaments (2), or only the primary medicament (1). The module (4) also contains a guard (42) that locks after dose delivery.