From Bulbapedia, the community-driven Pokémon encyclopedia.
Every region, starting in Johto, has an Herb Shop (Japanese: かんぽうや Kampo Shop). The herb shops sell bitter herbs. The herbs sold, which are the same in each region, are the Energy Root, EnergyPowder, Revival Herb, and Heal Powder.
The prices of the herbs, in all five regions with herb shops, are:
All four of the herbs in some way heal the Pokémon that they are used on but cause the Pokémon to be less friendly. The Energy Root heals a Pokémon's HP by 200. The EnergyPowder heals a Pokémon's HP by 50. The Revival Herb revives a fainted Pokémon with full HP. The Heal Powder heals any status ailment.