To enslave someone you need to have a free space in your cell (complete some quests from the naked engineer. Socket her name is iirc. She's in the mines) and have slave collars in your inventory (old collar in the debug menu iirc if you're using it)
Effects from pills are transformations that are applied to the character and you won't know the effect until it will happen. You'll get a small event on that when changing the location
They are always unknown. Check the icon. If it says "unknown effect (final stage)" then this particular transformation is finished.
There are 4 types of pills:
Pill that starts the (random) transformation
Stabilization pill that makes transformation permanent
Reversion pill that removes all non permanent transformations
And acceleration pill that makes transformations happen faster
I don't remember the exact names, but that's the effects
