system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why do some medications need to be directly injected into the bloodstream, while others can simply be injected into a muscle?
gpt
It depends on the situation. IV meds that go directly into the blood act faster and the dose can be changed easily. These are typically useful for inpatient care.

IM injections can be long acting medicines that stay in the muscle and slowly gets released over time. Or it could be something like Haldol where someone is acutely psychotic and it is easier to hit a muscle than it would be to setup an IV on someone who is trying to fight you off.