- Infusion: This method is used for drugs that are soft in nature such that water may penetrate easily into the tissues and the active constituents are water soluble. The drug to be extracted is placed at the bottom of an infusion pot, water is added and the contents are stirred occasionally. Another method of preparing the infusions is that the drug is enclosed in a piece of muslin cloth and suspended just below the level of water. After sufficient time period, the liquid is strained and dispensed. Infusions must be freshly prepared and consumed within 24 hours of its preparation. Examples are infusion of senna and infusion of quassia.
- Decoction: In this process, water-soluble thermostable constituents of hard and woody crude drugs are extracted. Water is used as the solvent. The size reduced drug material is boiled with the solvent for a specified time, usually 15–20 minutes. After boiling, the liquid is cooled and filtered more water is passed through the marc to produce the required volume. The decoction should be freshly prepared and consumed within 24 hours.
- Digestion: This process is a modified form of maceration in which the extraction of drugs is carried out by applying gentle heat to the substances being extracted. This method is applicable to those drugs for which moderately elevated temperature can be used and the solvent action of the menstruum is increased by gentle heat.
- Maceration
- Simple maceration for organized drugs: In this process, the extraction of drugs is carried out by placing the finely subdivided solid drugs in contact with the whole of the menstruum in a closed vessel for 2–7 days, with occasional stirring. The liquid is strained and the marc is pressed, adding the expressed liquid to the strained liquid. The combined liquids are clarified by decantation or filtration and the final volume is not adjusted.
- Simple maceration for unorganized drugs: In this method, the extraction of drugs is carried out by placing a weighed amount of drug in contact with four-fifths of the menstruum in a closed vessel for 2–7 hours, with occasional shaking. After the specified period, the clear liquid is decanted or filtered. The marc is not pressed and the volume is adjusted by passing more menstruum through the marc.
- Multiple maceration: Repeated maceration is more effective than single maceration. Active constituents left behind after first maceration can be extracted out in the next maceration. The marc is pressed after each maceration process. The quantity of menstruum to be used is divided into equal quantities and used for each maceration process. Maximum extraction is obtained in multiple maceration process, which can be done by double or triple maceration.
- Percolation: In this process, the suitably size reduced drug is moistened with sufficient quantity of menstruum, which is then packed in a percolator. The drug is allowed to remain in contact with the menstruum for 24 hours, after which more menstruum is added from the top and percolation is started. The required volume is collected, marc is pressed and expressed liquid is added to the percolate. The required volume is obtained by adding more menstruum and the mixed liquid is clarified by decantation or filtration. Preparations made by percolation process are tincture of belladonna, compound tincture of cardamom and strong tincture of ginger.
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