
If you're at the doctor's clinic and he says "ok, I'll need to inject you with this safe and legal substance", would you stop and take the vial of liquid to a lab to have it tested to make sure it's safe? Or would you trust a trained expert to do their job and not be lying to you?
I probably would trust the doctor because I'm not a professional sportsperson. But I would expect him to tell me what it was, what it was going to do for me (eg side effects "can I drink etc") but above all if, sometime in the future I was to become concerned about the safety of the product, I would expect him to be able to show my medical history.