CMS has issued guidance to Medicare Part D prescription drug plan (PDP) sponsors on steps they should take to prevent overutilization of Medicare Part D drugs, particularly painkillers such as opioids. Among other things, CMS: clarifies that regulations requiring prompt payment of clean claims do not require sponsors to pay claims they believe to be fraudulent, provided that pharmacies are given timely notifications of all defects or improprieties rendering the claim not a clean claim; reviews guidance on reporting cases of suspected fraudulent activity and drug-seeking behavior; discusses prior authorization options and retrospective review for protected class drugs, indicating that where a pattern of overutilization of opioids is determined through beneficiary-level retrospective review, sponsors can require documentation to determine medical necessity and deny payment for subsequent claims if insufficient evidence is obtained to substantiate Part D coverage eligibility; suggests that PDP sponsors promote less than 30 day prescribing of drugs that are more susceptible to abuse or diversion, especially opioids; and notes that CMS will be monitoring the use of these tools, and will issue compliance notices to sponsors that establish inappropriate controls.