Hello,
I gave my skeleton negative energy essence. The skeleton animated drinking it.
Then I proceeded to inflicht light wounds upon myself, rather than the skeleton being healed.
This persisted so it is not a one time thing.
Can confirm this.
Tried drinking myself and didn't have the opposite effect either.
Script potions will not work on companions, no matter what the companion is. IT will always fire on the player who activated it.
Inflict wounds potions that are *not* scripts should work though.