Apothecaries (Herbcraft) have a monopoly on the manufacture and sale of herbal based home remedies, herbal teas, poisons, drug, and legitimate potions some of which seem to have minor magical properties. These are based mostly on herbs and fungi.
Despite serious legal sanctions, un-guided sellers of potions are common, especially at fairs, thieves guilds, and back alleys. Some churches have exemptions to make potions and drugs specific to their divine domains (e.g. Priestesses of Halea can make and sell Aphrodisiacs while The Church of Peoni can supply potions that aid in healing.
The major differences with magical potions are herbal potions have a limited shelf-life and will go off potentially having adverse side effects.
Alchemists have a monopoly regarding the manufacture and sale of chemicals, flash-powders, explosives, oils, acids, poisons and products made from minerals. Skilled masters of the arcane arts often add magical properties to Alchemical preparations.
Poisoncraft combines elements of Herbcraft and Alchemy to create deadly poisons and toxins. Those skilled in the craft are also able to extract and combine toxins from various monsters and animals into their preparations. There is no guild regulating poison manufacture as it is generally proscribed.