The official Resins may be divided into the (1) Natural Resins, (2) Resins obtained from Oleoresins by separating the Volatile Oil by distillation, and (3) the Pharmaceutical Resins, prepared by precipitation.

When a concentrated tincture of a resinous drug is poured into a large quantity of cold water, the resinous matter becomes insoluble and is precipitated; this, after being washed, dried, and sometimes powdered, is termed a resin.

Resins are usually soluble in alkalies and insoluble in acids (dilute); for this reason the water used for precipitation is sometimes rendered slightly acid to favor the separation.

The three following are official:

Resina and Resina Copaibae are obtained as residue in the distillation of the respective Oleoresins, Turpentine and Copaiba. The natural Resins are obtained as exudates - e. g. R. Guaiaci.

The terms resin, resinoid, and concentration are also applied to a class of preparations used by eclectic physicians, prepared by this general process with some modifications. (See U. S. and Am. Disp.) They are named after their respective Drugs with the ending in, as in Glucosides, and must not be confused with the latter. While the Glucosides are usually the active medicinal constituents representing the drug, the resinoids, with the exception of those made from drugs whose active principles are resins, such as Cimicifuga and Podophyllum, are more or less inert, unreliable mixtures, too indefinite in their composition and strength for medicinal use.