Excipient (pharmacologically inactive substance)
What is it?
Lactose (C12H22O11) is milk sugar. It is a disaccharide composed of one galactose and one glucose molecule. In the pharmaceutical industry, lactose is used to help form tablets because it has excellent compressibility properties. It is also used to form a diluent powder for dry-powder inhalations. Lactose may be listed as lactose hydrous, lactose anhydrous, lactose monohydrate, or lactose spray-dried.
People who are lactose intolerant do not have the enzymes needed to digest lactose. Most medications do not contain enough lactose to cause lactose intolerance. But some patients with severe lactose intolerance may experience symptoms. Lactose can be found in birth control pills, and some OTC drugs to treat stomach acid or gas. Patients who are specifically "allergic" to lactose (not just lactose intolerant) should not use tablets containing lactose, or ask their health care provider prior to use.
 Dave RH. Overview of pharmaceutical excipients used in tablets and capsules. Drug Topics (online). Advanstar. 10/24/2008 http://drugtopics.modernmedicine.com/drugtopics/Top+News/Overview-of-pharmaceutical-excipients-used-in-tabl/ArticleStandard/Article/detail/561047. Accessed 08/19/2011
 Anon. Lactose Intolerance. National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health. NIH Publication No. 09–2751,June 2009; http://digestive.niddk.nih.gov/ddiseases/pubs/lactoseintolerance/#products. Accessed 08/19/2011