Which drug product is not classified as a controlled substance?

Ramelteon is the drug product that is not classified as a controlled substance. It is primarily used for the treatment of insomnia and acts as a melatonin receptor agonist. Unlike the other options listed, which are opioid analgesics and are associated with a potential for abuse and addiction, Ramelteon has a different mechanism of action and a lower risk of dependence. This distinction is significant, as controlled substances are typically those that have a high potential for abuse and are regulated by governmental agencies due to their effects on the central nervous system. As such, Ramelteon's classification reflects its safety profile and therapeutic use without the same level of regulatory concern compared to opioids like oxycodone, hydrocodone, and morphine.