An adapter for a drug mixing and injection system comprising - a first subunit comprising - a first opening adapted to hold a vial, said vial comprising a pierceable lid, and exhibiting a first longitudinal central axis, and - a second opening adapted to hold a reservoir comprising an injectable liquid, and exhibiting a second longitudinal central axis, wherein the first and the second openings (111, 112) are arranged to hold the vial and the reservoir in a position with the first and the second longitudinal central axes positioned at an angle below 75°; - a second subunit comprising an outlet port; and - a first cannula adapted to pierce the lid of the vial; wherein the first and the second subunits (110, 120) are engageable with each other, in such a way that the adapter has - a resting position in which the first and the second subunits (110, 120) are releasably or unreleasably connected and the first cannula does not pierce through the lid of the vial; and - an activated position in which the first and the second subunits (110, 120) are shifted towards each other and are in a position in which the first cannula pierces through the lid of the vial, characterized in that: - the adapter comprises at least one internal adapter channel enabling fluid connection between the first opening, the second opening, and the outlet port; - the second subunit further comprises a valve adapted to switch at least between - a first position enabling a first fluid flow between the first opening and the second opening, and blocking the fluid connection to the outlet port, and - a second position enabling a second fluid flow between the second opening and the outlet port, and blocking the fluid connection to the first opening; - the first cannula is positioned between the valve and the first opening and is further adapted to enable fluid connection between the vial and the at least one internal adapter channel upon piercing the lid of the vial, and and further characterized in that: - the reservoir is provided in the form of a syringe; and - the outlet port is adapted such that it can be used to perform an injection after attaching an injection needle to the outlet port. - a first subunit comprising - a first opening adapted to hold a vial, said vial comprising a pierceable lid, and exhibiting a first longitudinal central axis, and - a second opening adapted to hold a reservoir comprising an injectable liquid, and exhibiting a second longitudinal central axis, wherein the first and the second openings (111, 112) are arranged to hold the vial and the reservoir in a position with the first and the second longitudinal central axes positioned at an angle below 75°; - a first opening adapted to hold a vial, said vial comprising a pierceable lid, and exhibiting a first longitudinal central axis, and - a second opening adapted to hold a reservoir comprising an injectable liquid, and exhibiting a second longitudinal central axis, wherein the first and the second openings (111, 112) are arranged to hold the vial and the reservoir in a position with the first and the second longitudinal central axes positioned at an angle below 75°; - a second subunit comprising an outlet port; and - a first cannula adapted to pierce the lid of the vial; wherein the first and the second subunits (110, 120) are engageable with each other, in such a way that the adapter has - a resting position in which the first and the second subunits (110, 120) are releasably or unreleasably connected and the first cannula does not pierce through the lid of the vial; and - an activated position in which the first and the second subunits (110, 120) are shifted towards each other and are in a position in which the first cannula pierces through the lid of the vial, - a resting position in which the first and the second subunits (110, 120) are releasably or unreleasably connected and the first cannula does not pierce through the lid of the vial; and - an activated position in which the first and the second subunits (110, 120) are shifted towards each other and are in a position in which the first cannula pierces through the lid of the vial, - the adapter comprises at least one internal adapter channel enabling fluid connection between the first opening, the second opening, and the outlet port; - the second subunit further comprises a valve adapted to switch at least between - a first position enabling a first fluid flow between the first opening and the second opening, and blocking the fluid connection to the outlet port, and - a second position enabling a second fluid flow between the second opening and the outlet port, and blocking the fluid connection to the first opening; - a first position enabling a first fluid flow between the first opening and the second opening, and blocking the fluid connection to the outlet port, and - a second position enabling a second fluid flow between the second opening and the outlet port, and blocking the fluid connection to the first opening; - the first cannula is positioned between the valve and the first opening and is further adapted to enable fluid connection between the vial and the at least one internal adapter channel upon piercing the lid of the vial, and - the reservoir is provided in the form of a syringe; and - the outlet port is adapted such that it can be used to perform an injection after attaching an injection needle to the outlet port.