Change how they work, or raise the cooldown and limit the number you can carry.

This game is about pushing, defending, and applying pressure.  Your goal is to try to push your creep waves past theirs, and pressure opponents into defending their towers and getting them out of their lane so you can destroy their towers.  You do this either by killing them, or weakening them to the point where they have to go back to heal. 

As it stands, it's too easy (especially early on in the game where such things really make the biggest difference) to stay in your lane even after an opponent has applied strong pressure, simply because you can heal yourself up to 3 times to full health with healing potions (which you can afford easily with the gold you start out with).  This discourages early pressure because the ability to heal far outweighs the ability of characters to deal damage at early levels. 

It's also something of an issue late game, in my opinion.  Potions can be cast in battle (cast bar doesn't get interrupted) and heal players back up to full health (or almost full health).  Yes, there is a cooldown on them, but it's still pretty lame if you work hard to get somebody to low health and then they just pop a potion and get back to full health in a second.

In light of this, one of two things ought to be done:

1) Make them heal over time instead of direct heal.  Also, make their "cast bar" interruptable.  This ensures that they must be used out of combat to be effective.

OR

2) Raise the cooldown, limit the player to 1-2 potions of each type per slot, and make them instant.  This way they can be used as a quick "Oh Shit!" item to save you in a tight spot.  But once you use it, you can't use a potion again for a couple minutes.  This way if you're under a lot of pressure using a potion once won't stop you from being pushed back.  You have to pressure back, because you'll quickly lose health again and you won't have any more potions to pop once you do.