I’m trying to use Snorlax, belly drum, heavy slam in singles at the battle stadium but I got curious if Sitrus Berry would work after belly drum. If it doesn’t work, plz suggest a replacement item.
Yes, Sitrus Berry will still activate. Its only condition is if the Pokemon is on or below 50% HP, it has no limitation on the method it was achieved.
Source: Knowledge and rechecking on Pokemon Showdown.