SO when you're trying to slava some npc/multiple npc , Stimpacks kill them, healing powder doesnt work, and only option to revive them is using first aid skilll. Unles you feel like waiting for them to stand up of their own accord, with the new healing rates, this could take 20 minutes.
This is an excerpt from the wiki section on slavery:
To enslave, you will need :
Some healing stuff (Healing powders, stimpacks or high First Aid skill etc.).