Related to: Issue 1711, but not quite the same(that mostly revolved around adding an amulet or other wearable), and I didn't want to perform thread necromancy on that one.

I verified the existing behavior (permanent drained, not temporary) in prerelease 5.

Permanent stat boosts (from items) obviously can't be drained before your own stats - the only way to do that would be to drain the stat boosting effect of the item, which wouldn't work for artifacts etc - so it would be a confusing mechanic.

Temporary stat boosts, such as those from a potion of boost [stat] (are there other kinds? - wishes?) can be reduced before your personal stats - they go down over time anyway.

This would mean the stat drain:
1) Still has an effect (reduces that stat)
2) The effect is still permanent, from a certain point of view (you aren't getting that stat point back, you're closer now to having it actually drained)

This would make the potions somewhat more useful against vampires(since only some potions are needed), GUVs (it might now be worth downing a bunch of stat boosters as you got to the liches), and NV. (AD doesn't matter - all stat drains with him are "temporary") Random encounters with other things probably wouldn't be worth a potion since you'd have no idea what they'd drain.

This wouldn't be as effective a solution as those suggested in issue 1711, but it is not mutually exclusive with them, and it doesn't need a new item, just a small change to how drains interact with temporary buffs.