The active medicinal constituents, or principles, of crude drugs are obtained by extraction. Extraction is effected either by maceration, expression, and filtration or straining, or by maceration with heat, when it is called digestion, or by percolation. The liquid employed, termed menstruum (pl. menstrua), may be Water or Alcohol, or Alcohol and Water in various proportions, sometimes with Glycerin. A few drugs require alkaline menstrua, some acid menstrua, while the oleoresins are made with Acetone (except Cubeb, which is made with Alcohol).

The Infusions and Decoctions are the simplest preparations made by extraction, and represent most nearly all the soluble constituents of the drugs. But not all drugs are adapted to this method of extraction nor to this exceedingly effective, though not especially elegant, form of exhibition. Also infusions and decoctions spoil easily unless alcohol is added as a preservative.

The most generally convenient and effective class of extractive preparations are the Tinctures. They are the simplest form of alcoholic preparations, and the other more concentrated preparations are usually first obtained as tinctures and then concentrated by evaporation, so as to yield the fluidextract, extract, or resin respectively.