A decoction is a method of extraction by boiling herbal or plant material in water or any other solvent to dissolve the chemicals of the material. It is the most common preparation method in various herbal-medicine systems. Decoction involves first drying the plant material, then mashing, slicing, or cutting the material to allow for maximum dissolution, and finally boiling in water to extract oils, volatile organic compounds, and other various chemical substances. Occasionally, aqueous ethanol or glycerol may be used instead of water. Decoction can be used to make tisanes, tinctures, and similar solutions. Decoction is also the name for the resulting liquid.

Decoction is different from infusion and percolation, but the resultant liquids can sometimes be similar in their effects, or general appearance and taste. Decoction mashing is a traditional and intensive method of mashing used in brewing. In herbalism, decoctions are usually made to extract fluids from hard plant materials such as roots and bark. Decoctions can also be used as a compress (also known as fomentation) to apply the herb directly to the skin.

To make a decoction, the plant material is usually boiled for 1-2 hours in 1-5 liters of water, depending on the herb used. The resulting liquid is then strained and can be consumed as a drink, using about 1/4 to 1/2 a cup as needed. The type of herb used will further determine how much to consume. Depending on the herb, you may need to add a little honey or stevia to make the drink palatable. Many herbs make wonderful decoctions, such as burdock root for liver support, yellow dock root for anemia, and dandelion root for cleansing the liver.