The idea of "Alkahestry" is built on the practice of fashioning elixirs and, therefore, is mainly used for medicinal purposes; as such, the focus of the craft is the discovery of the Elixir of Life - the key to immortality and eternal vigor - as opposed to Amestrian Alchemy's preoccupation with the Philosopher's Stone's alchemical augmentation properties.
Four hundred years ago, the practices which would give rise to this Xingese alchemy could not be truly called "alchemy" at all, but a series of misguided attempts at mystical healing through the ingestion of various substances. In fact, it is said that three whole generations of the imperial family died from ingesting mercury because they believed that it promoted longevity. It wasn't until a mysterious figure they call "The Philosopher of the West", who had supposedly come from Xerxes, appeared in Xing with his alchemical teachings that Xingese Alkahestry was born - created from a melding of the new teachings and the old metaphysical healing practices.
May Chang is the only character shown in the series to use Alkahestry, though Scar's alchemy uses alkahestry principles. Van Hohenheim helped create Alkahestry, and has knowledge of it, but is never seen using it. Because of their differing origins, Father cannot control Alkahestry as he does Alchemy.