Drugs.com describes lactose monohydrate simply as milk sugar, a disaccharide composed of one galactose and one glucose molecule. The pharmaceutical industry uses lactose monohydrate for its compressibility properties that help in the formation of tablets. The industry also uses this substance to form a diluent powder for dry-powder inhalations.
Drugs.com also notes that lactose monohydrate has pharmacologically inactive properties. People who have allergies should not take tablets containing lactose. Most medications containing lactose monohydrate do not have enough lactose present to affect people who are lactose intolerant, namely, those whose digestive systems do not possess the enzymes needed to digest lactose. Lactose-intolerant patients should ask their physicians whether or not they may safely take certain medications containing lactose. Lactose may sometimes be listed on medication labels as lactose hydrous, lactose anhydrous or lactose monohydrate.
Medications containing lactose include birth control pills and some over-the-counter drugs used to treat stomach acid or gas. Drugs.com mentions a few other specific medications containing lactose monohydrate including acetaminophen and hydrocodone bitartrate, clonazepam, cyclobenzaprine hydrochloride, hydromorphone hydrochloride, meloxicam, methadone hydrochloride, morphine sulfate, nucynta tapentadol, oxycodone hydrochloride, promethazine hydrochloride and tramadol hydrochloride. Drugs.com notes that these medications come in different strengths from different manufacturers, so lactose-intolerant patients must keep this in mind when asking about particular medications.