Besides being available on the Grand Exchange, players may also purchase 3 dose potions from Uglug Nar for 200 coins once they've learned how to make the potion. To open Uglug Nar's store, simply give him a 3 or 4 dose Relicym's balm potion, for which he will pay 650 or 1000 coins respectively. Note that Uglug will buy these potions from players for 120 coins as well if he has none in stock, but it must be a 3 dose potion for him to make an offer.
Before the Evolution of Combat update, the main use of Relicym's balm was to cure disease. Depending on how long the player had been infected with disease, it took up to 3 doses to be fully cured; the more recent the infection, the more doses required.