An injection device for delivering a dose of medicament from a syringe, the injection device comprising: a housing ; a plunger moveably mounted within the housing; an actuation mechanism arranged to provide a forward biasing force to urge the plunger forward in use to express a dose of medicament; a trigger mechanism arranged to releasably hold the plunger against the force of the actuation mechanism; and a plunger velocity regulator comprising: a cam surface associated with one of the housing or the plunger; a collar axially coupled to the plunger, the collar comprising a cam member arranged to engage the cam surface during actuation movement of the plunger such that axial movement of the plunger relative to the housing causes relative rotational movement of the collar and limits the forward velocity of the plunger movement; characterised in that : the collar is configured as an intermediate drive member of the actuation mechanism and the actuation mechanism comprises: a first compression drive spring disposed between the collar and the housing or a feature fixed relative to the housing; and a second compression spring disposed between the collar and the plunger; wherein: the first compression spring is released upon release of the plunger by the trigger mechanism to urge the collar forward; the plunger and collar are coupled such that once the collar has rotated by a predetermined angular degree relative to the plunger, the collar is axially decoupled from the plunger; and upon decoupling of the collar and the plunger, the second compression spring is released to urge the plunger forward. a housing ; a plunger moveably mounted within the housing; an actuation mechanism arranged to provide a forward biasing force to urge the plunger forward in use to express a dose of medicament; a trigger mechanism arranged to releasably hold the plunger against the force of the actuation mechanism; and a plunger velocity regulator comprising: a cam surface associated with one of the housing or the plunger; a collar axially coupled to the plunger, the collar comprising a cam member arranged to engage the cam surface during actuation movement of the plunger such that axial movement of the plunger relative to the housing causes relative rotational movement of the collar and limits the forward velocity of the plunger movement; a cam surface associated with one of the housing or the plunger; a collar axially coupled to the plunger, the collar comprising a cam member arranged to engage the cam surface during actuation movement of the plunger such that axial movement of the plunger relative to the housing causes relative rotational movement of the collar and limits the forward velocity of the plunger movement; a first compression drive spring disposed between the collar and the housing or a feature fixed relative to the housing; and a second compression spring disposed between the collar and the plunger; the first compression spring is released upon release of the plunger by the trigger mechanism to urge the collar forward; the plunger and collar are coupled such that once the collar has rotated by a predetermined angular degree relative to the plunger, the collar is axially decoupled from the plunger; and upon decoupling of the collar and the plunger, the second compression spring is released to urge the plunger forward. <EOS>