Pharmakos berries are used in making Goblin potions, which are used during the Land of the Goblinsquest. These are given by the Makeover Mage for free. If one is already in the inventory, the Mage will say: "I think you already have some". However, multiple berries can be acquired by using the drop trick. The Wasteless herblore ability from Daemonheim rewards will also allow you to save the berries upon making the goblin potion.