just searching for 'magic' and found this post.
I had an idea long ago that is related to your idea. each character has 'life points' which is a pretty large total. like thousands of points. it never replenishes (or maybe it can be replenished through various nasty means, but thats another story)
as you naturally age, you loose life points. when you run out of life points you die.
but casting magic uses lifepoints, so the more magic you cast, the quicker you wizen and die.
so you could have these young vital magician characters who are full of spunk, but not wise enough yet to know much magic.
and these older, prematurely aged characters who have accumulated much practical magic knowledge and powerful spells in their lives but are too scared to use it very often...
just a throw away idea.
A problem with magic reducing HP as opposed to some sort of mana or fatigue is that you can't have spells that heal the caster. If this is irrelevant to you, then I don't see any major problems.
I do beleive that it will make characters more reluctant to use magic or play mages, however, as a couple spells might nearly deplete their health points, putting them even closer to death (and the probably have fewer HP than, say, a fighter, anyway.)
The above two posts were split from Magic mechanics (http://www.indie-rpgs.com/forum/index.php?topic=16847.0).
Steve, you are causing a lot of problems. You're posting impulsively and without much content. You're resurrecting threads past their allowed lifespans.
Do not post again until you have reviewed the sticky posts in the Site Discussion forum, in order to learn about the standards of the site. We don't ban people or delete posts here. The standards are enforced in a different way, and I'm putting you on notice that any posts from you, from now on, must accord with them perfectly.
Best,
Ron