The best way to go about it, in my opinion:

Normal Difficulty - Help restores 1 HP
Hard Difficulty - Help stabilizes an ally. Medicine Kits can be used in combat to grant 1 HP, or out of combat for a heal
Tactician - Medicine Kits can be used in combat to stabilize an ally in combat, or out of combat for a heal

Seems like a pretty fair way to go about it for each difficulty.