A plunger seal for a drug delivery device may have a mobile and an enhanced sealing parked state. Optionally, the cartridge is stored with the plunger seal in the parked state. Optionally, drug discharge occurs with the plunger seal in the mobile state. For example in the parked state there may be increased normal force between the plunger seal and an inner wall of the cartridge. Optionally there is limited deformation of the plunger seal between the parked and mobile states. Optionally the plunger seal is biased to the parked state. Optionally, a distal force switches the plunger seal to the mobile state. For example, the plunger seal may have an inner cavity that is expanded radially by core. A biasing element optionally biases the core wedging it proximally to the parked state. A distal force on the core may push it distally to the mobile state.