I am going in for total hip replacement surgery next Monday and was recommended to drink “ensure clear” 3 hours prior to surgery. It has ‘whey ” and not cholov yisroel.
Can I drink it or do I need to do hatoras Nedarim?
Regarding hataras nedariim for someone who does not drink cholov stam, and for whatever reason has to now drink it, as in your situation. R’ Moshe Feinstein zt”l writes that it depends why you abstained until now from drinking cholov stam. If you didn’t drink it because you thought that it is ossur to drink then you don’t have to be matir neder, however if you didn’t drink it because you thought that it a good thing to be machmir on, but it isn’t really assur, then you should be matir neder.
Igros Moshe Y:D 1-47.