Which of the following is not classified as an opioid?

Cyclobenzaprine is a muscle relaxant that is primarily used to relieve muscle spasms. It works by acting on the central nervous system, specifically influencing the brain and spinal cord to relax muscles, but it does not interact with opioid receptors in the way that opioids do. Opioids, like heroin and oxycodone, are derived from opium and are specifically designed to relieve pain by binding to opioid receptors in the brain and other areas of the body, producing effects such as pain relief and sedation. Meth, while not an opioid, is a stimulant and does not share the same effects or classification as opioids, but it is still not a muscle relaxant, like Cyclobenzaprine. Therefore, Cyclobenzaprine is distinct from the opioid category, confirming its classification as the correct answer for this question.