Additional prevalent barriers included lack of knowledge about illness and treatment, side effects, and other provider factors, including patient-provider trust, patient satisfaction, and other communication issues. Barriers like health literacy, forgetfulness, transportation, access to care, and cognitive function and memory were rarely assessed in these studies. Regimen complexity and costs were evaluated in several articles but not included in this review to prevent duplication with recently published systematic reviews. Four of the five potential barriers most commonly studied in the articles reviewed (depression, beliefs about medications, number of prescriptions, and social support) are described in more detail next. Perceived health status had no relationship to medication adherence in the articles studied.