There's nothing wrong with that statement, the medical background checks but it loses veracity when it comes to the availability and methods to extract said medical supplies since most standard hospitals/clinics have every item accounted, making them hard to steal since they are sometimes locked and guarded by other medical staff. Now, that can also be bypassed, since the missing items can go missing with none the wiser (being friends with that staff or simply your turn to guard), though it requires that this occurs in a sizable institution were the items could be much more easily subtracted. Another possibility is that the items are bought, but here comes the kicker: there are no such fast-acting medications to induce sleep and the ones that do, require oral administration. Now if we are to talk about the method through injections (somewhat fast-acting, requires more precision and time to start having an effect), it is hard to believe that both girls got overpowered by the red-she-demon and got injected at the same time, I mean more than likely one of them could have been taken down, but both...
My final statement, regarding the ending: If you never interacted with Leah, and you shut down any interactions with her, why does the MC even decide to follow her to her apartment? I mean, at that point she is nothing more than a stranger/acquaintance at most, that doesn't hold any value to you. Obviously, the MC is devasted and on drugs, but it is still, a bit of a stretch to suddenly jump into the arms of a stranger, at night and confide with her everything while going to their home.