Not an injection, but on during one particular inpatient, by pdoc told me ahead of time he would be having me take some meds that would normally be as needed round the clock for a few days because he really just wanted me to sleep and reboot for a couple of days. It was actually quite helpful, and I was glad he discussed it with me ahead of time so I was aware of what he was doing, why, and what effect it would have on me.