system
Given the following post, respond as if you're commenting on Reddit:
human
eli5- When you get a shot with a needle how does the meds stay in the body instead of just coming right back out the hole the needle made? Is it different for IM and IV?
gpt
The needle is very tiny and the skin is elastic enough that not a whole lot can pass back through the hole left. In addition, the creation of the hole causes the body to begin the repair process, which fills the area with blood that sort of gets in the way of anything trying to get in or out - which is why some people bleed from injections. There simply isn't enough medication injected to force it's way back through all that, because it's just as easy to disperse throughout the muscle.