Opioid use disorder is a major public health problem, and opioid replacement therapy with buprenorphine (BPN) is a clinically effective and evidence-based treatment for it. To deter misuse of the tablet through the injecting route, BPN coformulated with naloxone (BNX) in 4:1 ratio is available in many countries. Despite this, significant diversion and injecting use of the BNX combination has been reported from across the world. In this article, the pharmacological properties of BPN and BNX and the evidence for their diversion are reviewed. Also, a critical examination is made of the evidence supporting the role of naloxone in reducing the agonist effects of BPN when used through the injecting route. Based on this evidence, a hypothesis explaining the continued diversion of BNX has been proposed.