Decoction is one of the oldest documented methods of extracting pharmacologically active compounds from plant material. Unlike an infusion, which uses water below boiling point and is suited to delicate aerial parts such as leaves and flowers, a decoction applies sustained, direct heat , generally a low boil or gentle simmer maintained for 20–45 minutes , to break down the tougher cell walls and lignified tissues characteristic of roots, bark, dried berries, and seeds.
The chemistry involved is selective. Sustained heat draws out water-soluble constituents including polysaccharides, tannins, alkaloids, and certain glycosides, whilst driving off more volatile aromatic compounds that would ordinarily be preserved in a cold or short-steep extraction. This makes the technique well-suited to plant parts with dense cellular structure but poorly suited where thermolabile or volatile constituents are the primary material of interest.
Decoction features across most documented traditional medicine systems. It is a defined preparation method in Traditional Chinese Medicine (TCM) pharmacopoeias, in Ayurvedic practice (where the equivalent preparation is called kwatha), and throughout the documented history of Western herbal traditions from Dioscorides' De Materia Medica (c. 50–70 CE) forward. In contemporary pharmaceutical and phytochemical research, standardised decoction procedures are used as one reference extraction method when characterising the constituent profile of crude plant material.
Decoction as a preparation method carries no inherent therapeutic claim. The pharmacological activity , or absence of activity; of any resulting preparation depends on the specific plant material used, its constituent chemistry, the concentration achieved, and the biological context in which any constituent is studied. Regulatory classification of a decoction-based product in Australia depends on its ingredients and intended purpose, and may fall under the Therapeutic Goods Administration's (TGA) framework for listed or registered medicines, or outside it entirely.
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