MK-4101 is a potent and selective antagonist of the orexin OX1 receptor. It has been primarily investigated for its potential in treating addiction-related behaviors, particularly cocaine dependence. By blocking the OX1 receptor, MK-4101 modulates neurobiological pathways involved in reward and reinforcement, reducing drug-seeking behavior in preclinical models. It shows promise as a pharmacological agent for substance use disorders, especially where current treatment options are limited. Research also suggests possible applications in anxiety and stress-related conditions due to the role of the orexin system in regulating emotional states. However, its development remains in early stages, with most data derived from animal studies.