An automatic injection device has an insertion needle configured to be inserted into a patient and a drug container which contains a pharmaceutical product and includes a plunger. The automatic injection device also has a fluid path which fluidly connects the drug container to the insertion needle, and a drive system configured to cause linear movement of the plunger to force the pharmaceutical product into the fluid path. The passive drive system has a movable element. The movable element has a shape memory alloy and is configured to change shape to move the plunger.