A plant was rarely a medicine simply by existing. Healers dried leaves,
crushed roots, boiled barks, infused flowers, distilled aromatic waters,
expressed oils, prepared syrups, mixed poultices, and combined many
ingredients in compound prescriptions. Timing, season, storage, and dose
could matter as much as the named plant.
That practical work made herbal medicine part of the history of
pharmacy. Apothecaries kept stocks, prepared formulas, substituted
ingredients, sold simple and compound remedies, and negotiated authority
with physicians, surgeons, guilds, and customers. Their shops made
materia medica more visible, commercial, and repeatable. The
Pharmacopoeia Londinensis (1618), issued by the Royal College of
Physicians, was an early official pharmacopoeia that set standard names,
strengths, and preparations for the drugs apothecaries were expected to
supply.
Herbal practice also carried risk. Plants could be ineffective,
adulterated, contaminated, misidentified, poisonous, or harmful at the
wrong dose. Historical practitioners knew that some remedies were
dangerous, but they did not always have stable tools for measuring
potency or tracing adverse effects. The sixteenth-century physician
Paracelsus argued that the dose, not the
plant's reputation, determined whether a substance healed or harmed, and
he pushed medicine toward chemical preparation and measured dosing.