Methyl cellulose (or methylcellulose) is a chemical compound derived from cellulose. It is sold under a variety of trade names and is used as a thickener and emulsifier in various food and cosmetic products, and also as a bulk-forming laxative. Like cellulose, it is not digestible, not toxic, and not an allergen. In 2017, it was the 272nd most commonly prescribed medication in the United States, with more than one million prescriptions. Uses
Methyl cellulose has a wide range of uses. Medical
Constipation
Methyl cellulose is used to treat constipation. Effects generally occur within three days. It is taken by mouth and is recommended with sufficient water. Side effects may include abdominal pain. It is classified as a bulk forming laxative. It works by increasing the amount of stool present which improves intestinal contractions.It is available over the counter. It is sold under the brand name Citrucel among others. Artificial tears and saliva
The lubricating property of methylcellulose is of particular benefit in the treatment of dry eyes. Solutions containing methyl cellulose or similar cellulose derivatives are used as substitute for tears or saliva if the natural production of these fluids is disturbed. Medication manufacturing
Methyl cellulose is used in the manufacture of drug capsules; its edible and nontoxic properties provide a vegetarian alternative to the use of gelatin. Consumer products
Thickener and emulsifier
Methyl cellulose is occasionally added to hair shampoos, tooth pastes and liquid soaps, to generate their characteristic thick consistency. This is also done for foods, for example ice cream or croquette.
A better way is to first mix the powder with hot water, so that the methyl cellulose particles are well dispersed (and so have a much higher effective surface area) in the water, and cool down this dispersion while stirring, leading to the much more rapid dissolution of those particles. See also
Carboxymethyl cellulose
Ethyl cellulose
Ethyl methyl cellulose
Hydroxypropyl cellulose
Hydroxyethyl cellulose

References
Further reading
Cathleen Baker (1984). Methylcellulose & Sodium Carboxymethylcellulose: An Evaluation for Use in Paper Conservation through Accelerated Aging. Preprints of the Contributions to the Paris Congress, 2–8 September 1984: Adhesives and Consolidants, pp. 55–59. International Institute of Conservation. Robert L. Feller and Myron H. Wilt (1990). Evaluation of Cellulose Ethers for Conservation (free fulltext). Getty Conservation Institute. Pijper A (March 1947). "Methylcellulose and Bacterial Motility". J. Bacteriol. 53 (3): 257–69. doi:10.1128/JB.53.3.257-269.1947. PMC 518306. PMID 16561270.