In our health system, there is "shot time" - 15 minutes - for any IM injection. That is just to observe for any acute/allergic reactions.
As far as things that might sedate, like opiates, or PO Flexeril, or Norflex, patients either have to have a driver, or they can wait until the medication effect wears off. As I tell the patients, even with a prescription, you still are not legal to drive under a medication effect (just like it's legal to drink a beer, but not to drive).