Victor has always been sinister and not one to let things go. Appears he is still upset that Sharon left him for dead, didnt like the way she ran his company or burning down that outdated, dreary ranch. Actually she did him a favor burning that thing down. So he decided to switch her meds and tried to get Mason to do it but he was not successful. Not one to let a roadblock stop him, I am sure he found a way to switch her meds.
Sharon has always been pretty sinister herself, making out with him when he was hopped up on pain meds and letting him take the blame when Nick saw.
Normally I would never take Victor's side, but if someone burned down my family home, destroyed my company and let my family think I was dead, I would want payback too.
She deserves way more than a medication switch. He should burn down her home, have Faith taken away because she is nuts and have her committed to the loony bin, where she clearly belongs.