AA - Yep, it was a potion someone was mucking about with way back when so they could get all the benefits of having dementors without actually having to deal with dementors. Which considering the effects on any guards near Azkaban, I'm assuming a lot of people have tried that.

It didn't quite work because it doesn't suppress anyone's magic and without the constant drain on happy thoughts, it's easy for a strong willed person to mostly brush it off even if they are more prone to severe depression afterwards. It is why I made Graves' character duty-driven. Honour and duty are not exactly happy thoughts, but they'll sustain people with nothing else left and with no hope of reward.

I don't think the potion origin will become relevant later on, but we'll see. I don't really have much of a plan.