Damage not triggering in build

Hey guys, I'm using this script for my player's health:

 var health=10;
  
 function OnDamage(damage:int)
 {
 health -= damage;
 }
 function OnGUI()
 {
     if(health <- 0)
     {   
     Time.timeScale = 0.0;
         if(GUI.Button(Rect(Screen.width/2-100, Screen.height/2-50, 200, 100), "Retry?"))
         {
             Application.LoadLevel(0);
         }
     }
 }

The script works perfectly when testing in unity itself, but when I build and play it, the timeScale stays at 1.0 and the retry message doesn't display when I take damage.. I've only been using unity a few days, what am I doing wrong?