How long is it supposed to it take for vitamin d (prescription) to work?

~3 mo, Maybe Never?: Work by what criteria? Over last few years, my experience with people who have chosen vit d3 rx (written by myself), have essentially always being given vit d2 50k iu pills by pharmacies (despite this substitution being illegal). A large minority of people do not convert d to d2 or d2 to d3 well. I have seen the quest lab d3 conc. Either not improve or even go down in people saying they took rx.