Diabetics give themselves several injections a day. True, these are injections into the subcutaneous fat layer and this is the easiest way to do it yourself. Intramuscular injections are more difficult to do, but also quite possible, the main thing is to find a suitable place, relax the muscle and not react to pain.
You can do the injection yourself.
As for intravenous injections, you need to be able to do this and know:
the rules of asepsis and antisepsis - so as not to infect yourself corny ...
be able to apply a tourniquet;
take the right drug;
find and "feel" the vein;
These skills are not difficult, but require understanding and knowledge.