In addition, the following contribute: Financial and physical constraints, which may make purchasing drugs difficult Cognitive problems, which may make taking drugs as instructed difficult Use of multiple drugs (polypharmacy) Use of drugs that must be taken several times a day or in a specific manner Lack of understanding about what a drug is intended to do (benefits) or how to recognize and manage adverse effects (harms) A regimen using too frequent or too infrequent dosing, multiple drugs, or both may be too complicated for patients to follow.