What does dispel do?

[Julliard-trained dermatologist]

As the title says, what does it do and how does it work? I tried using it whenever an enemy casts some sort of spell that effects my stats but nothing seems to happen.

[PainkilleR]

https://en.uesp.net/wiki/Oblivion:Dispel

[Heimdall313]

Drain spells affect you, you have to dispel yourself.
Dispel on target is only really useful to destroy Shield spells and dismiss summons, but NPCs typically have obnoxiously large magicka pools and will simply recast more than you can dispel.
Most Drain spells they use are inane and don't detriment you at all, or only drain a minor 15 HP or something.

Dispel magnitude has to be strong enough to dispel ALL active effects, otherwise it fails entirely and removes nothing. It will also remove your own buffs (ie, your Defend spell is removed along with enemy's Drain Fatigue).