Glycerol is an osmotic dehydrating agent with hygroscopic and lubricating properties. When administered orally or parenterally, glycerol increases plasma osmolality, causing water to be transferred from the extracellular space to the plasma by osmosis. Oral glycerol can be used for short-term reduction of vitreous volume and intraocular pressure before and after ophthalmic surgery, and also as an adjunct to acute glaucoma treatment. Glycerol can also be applied topically to reduce corneal edema, but because of the transient nature of this effect, glycerol is limited to use as an adjunct to ocular examination and diagnosis. Glycerol is administered transrectally as a single dose suppository or solution to promote fecal evacuation and is used to treat constipation. Glycerol usually takes effect within 15-30 min. Glycerin is also often classified as a solvent-based laxative, but is often applied as an adjunct or alternative because of its local irritant effect; it also has a lubricating and stool-softening effect. Glycerin is also used in cough preparations as a moistening agent that acts as an indirect peripheral cough suppressant by providing a protective layer over the sensory receptors in the pharynx. Glycerol has a variety of uses in pharmaceutical formulations; including as a carrier and solubilizer, sweetener, preservative in certain liquid drugs, plasticizer in film-coated tablets, and tension regulator. It is also used as a lubricant in certain topical formulations, such as eye drops, creams, and topical skin lotions, because of its hygroscopic properties, which enhance water retention when the drug is absorbed. Glycerin is used as a lubricant and softener in ear drops for the removal of ear wax.