Peripherally selective trans-3,4-dimethyl-4-(3-hydroxylphenyl)piperidine opioid antagonists were developed for the treatment of gastrointestinal motility disorder by Zimmerman and his coworkers. From that, they derived the 4-(3-hydroxyphenyl)-3,4-dimethylpiperidine scaffold with functional groups spanning various sizes, charge, and polarity to reach peripheral opioid receptor antagonism while decreasing CNS drug exposure. The in vitro μ-Ki, in vivo AD50, and ED50 and peripheral index (ratio) was examined for several selective analogs, and from that, they found out that the trans-3,4-dimethyl-4-(3-hydroxyphenyl) piperidine, Alvimopan, gave the best results. The large zwitterionic structure and the high polarity prevents Alvimopan from crossing the blood–brain barrier, potency at binding peripheral MORs is thereby 200 times that of central MORs.