Saline injections on general are rare unless it is an iv drip.
Do a quick search to see what is in the “placebos” drug companies use as controls.
Hint: not saline
We used saline for injection training in the Army Combat Medic Course in 2002.
You simply take a syringe, draw saline from a bottle, vial, or even an IV bag and you have a saline injection.