Getting a first person controller to collide with various gameObjects.

I am trying to get my first person controller to collide with different objects. The purpose of this is to get my character to take damage when an enemy collides with it. I do this by using a damage script with an OnCollisionEnter function to send a message to the first person controller to take damage to a health variable. I figured out that nothing but my fireball prefab will register a collision with my first person controller. Please help me, I've tried everything I could think of.