system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why flu shots can go into a muscle but other stuff needs to go into a vein?
gpt
It depends on how fast you need it to act. Injecting into the muscle tissue is easiest and entails the least amount of risk. The drug is then absorbed through the fluids around the cells and eventually into the bloodstream. When you need something to act faster, though, you inject directly into the bloodstream where it can then be carried throughout the body within a matter of minutes.