Control measures designed to prevent the misuse of opioid medicines can often unintentionally restrict legitimate medical use, leaving patients with cancer in pain. This study aimed to develop and validate an assessment instrument based on WHO policy guidelines to systematically identify legal and regulatory barriers to opioid access in 11 European countries (Bulgaria, Cyprus, Estonia, Greece, Hungary, Latvia, Lithuania, Serbia, Slovakia, Slovenia, and Turkey) as part of the Access to Opioid Medication in Europe project. Relevant legislation and regulations were independently assessed by three reviewers and potential barriers were identified within nine categories including prescribing, penalties, and others. Potential barriers were identified in all countries, ranging from 22 potential barriers (Cyprus) to 128 potential barriers (Lithuania). The total number of barriers in a single category varied from one (Slovenia, usage category) to 49 (Greece, prescribing category). Differences, such as prescription validity, varied within one category, ranging from 5 days (Hungary) to 13 weeks (Cyprus). The results of this Review should give rise to a national review and revision of provisions that impede access to opioids, disproportionate to their (intended) benefit in preventing misuse, in these 11 European countries.