Disclosed is a method and an auto-injector for administering a medicament. The auto injector comprising: a housing; a cartridge receiver configured to receive a cartridge comprising a first stopper; a drive module coupled to move a plunger rod between a retracted plunger rod position and an extended plunger rod position, the plunger rod being configured to move the first stopper; a resistance sensor configured to provide a resistance signal indicative of resistance against movement of the plunger rod; and a processing unit coupled to the drive module and to the resistance sensor. The processing unit being configured to: control the drive module to move the plunger rod towards the extended plunger rod position with a plunger rod speed; determine plunger rod position; receive the resistance signal; and control the drive module to adjust movement of the plunger rod if the resistance signal is indicative of resistance against movement of the plunger rod above a high resistance threshold, wherein the high resistance threshold is based on the plunger rod position.