"With all due respect" (which makes whatever I say respectful!), depending on the substance or not, and with a micron filter, RNs do their shots the same as I once did. Sterile procedure/protocol.
Example: liquid morphine sulfate, betadine/alcohol swipe, register, slide in. This is no different than a hospital injection.
I will agree that the method itself is addictive in and of its self. Flake cocaine was my DOC. Of course it was not pharmaceutical, and I used it intranasally. Eventually, friends were IVing it in front of me. Observing this, I eventually gave it a shot, no pun. This was in the 1980s, when 1/4g was a huge/massive dose, one way or another. After a prolonged session, I decided to IV .2g. Risky business to say the least, but it became a logical ROA after that. Frankly, smoking base cola is in some ways far worse.