Most injections involve the administration of some local anaesthetic  and the decision about whether a person will be likely to be able to drive following injection should be based on a number of factors.  You should therefore discuss this with your practitioner. 

If you have received analgesia in the form of Entonox gas during your injection procedure, you should also wait at least 30 minutes before driving and again, you should only do so if you feel fit to do so.

Remember, you should only drive if you feel fit to do so, and if you consider that you would be able to perform an emergency stop if it was necessary to do so.  To do otherwise  could invalidate your insurance policy.