I have been playing Paladin's Quest lately, and one of the more unusual features of the game is that there is no MP; spells consume HP instead, and am wondering what other games take this approach. One nice thing about Paladin's Quest is that HP is actually easy to restore, so you don't have to hold back on your use of spells, unlike most RPGs if that era.

I remember Betrayal at Krondor using HP for spells, but I only saw part of the game played, and never actually played it myself. (Are the other Krondor games like this?)

What other games take this approach?

Diablo 2. There is a spell the Paladin has that takes away HP called Sacrifice.

ADOM allows casting from hitpoints if you don't have enough power points.

Forbes Corporate Warrior was an FPS where your health (cash) was also used as ammunition. As an aside, don't play that game.

Tides of Blood (a Warcraft 3 MOBA from before the term MOBA existed) had one hero, the Blood Mage, who used HP instead of mana.

Are there any games that start draining your HP if you run out of MP and keep casting spells?

I seem to recall that I've played some but I don't remember their names.

the PATH skill overhaul for Titan Quest: Anniversary Edition has a tree that use HP as spell fuel... its fantastic and really adds a new dimension to the game, i cant stop playing it ^_^

Real life, where if you try yelling "AVADA KEDAVRA" at a gang of tough guys, they'll beat you up.

Please do not inquire as to how I know this.

The Sega Genesis version of Shadowrun.

Not sure, but doesn't one race of pseudo-vampire families, in Masquerade, function like that ?

SMT Nocturne and Digital Devil Saga physical skills use HP. And Persona I think.

If you have not played Betrayal at Krondor, now is a good time, still the best PC RPG ever made for me.

I can't think of a game that does this, but SaGa frontier 2 does something similar.

If you don't have enough WP or SP to use a skill, you can still use it, but it will cost you 1 LP. Now LP is different from HP; it is much harder to restore, and the amount a character has does not increase through combat the way other stats do. I believe LP totals range from 6 or 7 to 23 at most. Running out of LP kills the character, and the character can't easily be brought back (in particular, there's no way to do so during battle), and if the main character runs out of LP, it's Game Over. By contrast, being reduced to 0 HP is easily remedied with a healing spell.

I don't know any off the top of my head, but there is the Cast From Hitpoints trope.

Castlevania Order of Ecclesia has at least one.
The ultimate instantly kills you though.

Albion works like this.