It goes without saying that poor adherence to treatment regimens leads to poorer clinical outcomes in chronic medical conditions.
A study published last year in "The Psychiatrist", and another more recent article in "Annals of Internal Medicine", examined as the main measure of adherence whether patients collected prescribed medications from a pharmacy (and not, in addition, whether the medication was consumed).
In "The Psychiatrist" article, the analysis suggests that supervised consumption and a shorter duration of treatment were the most significant predictors of non-adherence: So, although supervised consumption of methadone reduces the risk of diversion and methadone-related deaths, it may increase the risk of decreased adherence. Perhaps patients do not appreciate being observed so carefully, the resultant increase in illicit heroin use notwithstanding.
The "Annals of Internal Medicine" article found the extremely low rate of opiate abandonment most likely indicates less cost-sensitivity compared to other drugs, and a greater demand for opiates. Of course, patient addiction or plans to divert opiates will also contribute to reduced rates of abandonment. This leads in turn to one of the musings offered by the authors of the study: While prescription abandonment is inefficient for the pharmacy, clinically-speaking not all abandonment is bad. For example a patient's symptoms may have resolved, and thus a prescribed "as-needed" medication is no longer needed. Also, the act of purchasing a medication does not guarantee the patient will adhere to the recommended treatment.