Which opioid is currently the only injectable agent not classified as a controlled drug in the U.S.?

Nalbuphine is distinguished as the only injectable opioid that is not classified as a controlled substance in the U.S. This characteristic stems from its unique pharmacological profile. Nalbuphine acts as a kappa agonist and a mu antagonist, which allows it to provide analgesia while having a lower potential for abuse compared to other opioids. This atypical action makes it less likely to produce the euphoric effects often associated with traditional opioids, which are typically the focus of controlled substance classifications.

In contrast, agents like buprenorphine, fentanyl, and meperidine are controlled substances due to their higher potential for abuse and dependence. Buprenorphine, though used in pain management and as a treatment for opioid dependence, is classified as a controlled substance because it can still provoke opioid-like effects. Fentanyl and meperidine, both potent opioid analgesics, are also tightly regulated due to their risk of addiction and serious adverse effects.