First question, according to xXToothless113Xx
"you need the basic restrain potion recipe to craft the strong one. if you don't know it you can't craft the strong version which is what the quest asked for. you learn the basic one from Bernard on his urges quest."
Second question, if I remember correctly, you can get a recipe of restrain potion after you receive a quest from him and learn it from a notebook at your home. But if you mean a medicine in Bernard's sickness event, you need to study it yourself from a notebook at your home.
