It's not mandatory I personally never checked anyone's Social pages since it's technically their personal lifestyle, but I have known owners and other managers that do check before hiring. Now with that said after hiring someone if they tend to come into work with reasons for me to believe they were on drugs or other issues I would then check to see if they were posting something about that issue online.
I've always told employees and close friends to be careful about what you post and if you do post something that you don't want employers to see post it so only friends can see not the public.
Sorry not a straight forward answer but regardless, I hope this helps.
CVS managers don't, but HR might