A reservoir (31) with at least one flexible section for use in a medicated module (4) for an injection system to co-deliver at least two medicaments is disclosed where a primary delivery device (7) containing a first medicament accepts a medicated module (4) containing a single dose of a second medicament (2) and where both medicaments are delivered through a single hollow needle (3). The reservoir (31) comprises one or more slit valves (44, 45) to allow for delivery of the first and second medicaments. The medicated module (4) also contains a needle guard (22) that engages a housing (43) of the reservoir (31) to open the slit valves (44, 45).
