An injection system for co-delivery of two medicaments (1, 2) having a drug delivery device (7) containing a primary reservoir (11) containing a first medicament (1) and having a secondary reservoir (5, 17, 30) containing a second medicament (2) where the drug delivery device (7) has only one dose setter (12) for the primary reservoir (11) and that automatically determines the dose of the second medicament (2). Both medicaments (1, 2) are delivered through a single dispense interface (3, 16, 21, 31).
