Please help with While Loops

Ok, I have been coding for about 9 hours straight now and I think I am being monumentally dumb here.

I have this code that poisons the player, but it never un-poisons the player because the timer never reaches zero. It counts 4,3,2 and then stops.

I'm tearing my hair out here as I cant see why its not finishing the loop! Please can someone point out the obvious please!

     public IEnumerator Poisoned(int timer, float delay, int amount)
     {
         if (isPoisoned == false)
         {
             int tempTimer = timer;
             while (tempTimer != 0)
             {
                 isPoisoned = true;
                 currentHealth -= amount;
                 yield return new WaitForSeconds(delay);
                 tempTimer -= 1;
                 Debug.Log("!" + tempTimer);
             }
             isPoisoned = false;
         }
     }