Glycerin is a pharmaceutical preparations of glycerol. GLycerin is a clear, syryp-like liquid and is obtained as a by-product of saop, the fermentation of carbohydrates, and through other chemical reactions. Glyerin is important clinically and commercially. IT can be administered orally as a diuretic to reduce intraocular (within the eye) pressure. Glycerin can be given rectally to promote catharsis. In pharmaceuticals and foods, glycerin can be used as a humectant (moistening agent) or solvent.