From Halopedia, the Halo wiki
A herbal synthesizer is Forerunner technology utilized by the Covenant. It is used to provide remedies to a variety of ailments, one of which is overuse of Hookah Tobacco. They are used exclusively by ascetic San'Shyuum clerics.
Once a prescription is input into the synthesizer, it can produce a remedy via a delivery tube. A cleric used one of these machines to provide a remedy for the Minister of Fortitude.