Pharmacists may be contributing to unintentional medication nonadherence in their patients by labelling prescription medications in an unclear way. Many patients have low literacy, and even those with adequate literacy have trouble understanding some prescription label directions. Results of studies determining prevalence of low literacy and low health literacy are reported and studies that demonstrate patient understanding of commonly used label instructions and auxiliary labels are summarized. Strategies that might increase understanding of prescription labels for all literacy levels include using plain language, eliminating unnecessary words and phrases, and managing the way dispensing software translates commonly used abbreviations.