The present invention pertains to a medical device to allow a user to perform a self-administration of a drug. The present invention provides a power pack for use with an autoinjector, and an autoinjector having the power pack. The power pack includes a body having a canister to hold a liquefied gas, and a flow regulator for controlling a rate of exit flow of a gas from the canister to apply an adaptive force to a drug in a container associated with the power pack. The autoinjector also includes a main body having a container for holding the drug and a needle coupled to the container. The adaptive force provided by the gas provides for a smooth and controlled delivery of the drug from the container.
