According to a systematic review of 38 studies, the prevalence of illicit opioid use among pain patients who have opioid prescriptions ranges from 0% to 62%, with a median of 8.7% and a mean of 14.5%. The variation in the estimates depends on several factors, such as the definition of illicit use, the type and duration of pain, the source and method of data collection, and the sample size and characteristics. This use is a complex and multifaceted phenomenon that requires careful assessment and management by healthcare providers.