Backflow prevention mechanism for drug delivery device

A drug delivery device comprising:

• a housing defining a shell and an inner volume;
• a container at least partially disposed within the housing, the container having an inner volume adapted to contain a medicament to be administered to a user;
• a drive mechanism at least partially disposed within the housing, the drive mechanism adapted to exert a force to urge the medicament out the container;
• a needle assembly at least partially disposed within the housing, the needle assembly adapted to insert a needle or a trocar into the user's skin and to subsequently retract, thereby leaving a cannula within the user's skin for a period of time at least until the drive mechanism urges the medicament out the container;
• a fluid flow connection coupled to the container and the needle assembly, the fluid flow connection adapted to allow the medicament to flow from the container to the needle assembly;
• and
• a backflow prevention mechanism disposed within a coupling region between the container and the needle assembly, the backflow prevention mechanism comprising at least one flow restrictor to restrict a fluid from flowing from the cannula to the container, thereby reducing and/or eliminating clot formation during the period of time at least until the drive mechanism urges the medicament from the container to the needle assembly,
• wherein the coupling region includes an upstream portion and a downstream portion, the upstream portion having an upstream diameter larger than the flow restrictor and the downstream portion having a downstream diameter smaller than the flow restrictor.