Which of the following is not a category of prohibited drugs?

Opioids, as a category of drugs, do fall under the broader classification of controlled substances or prohibited drugs in various jurisdictions due to their potential for misuse and addiction. They are typically used for pain relief but can be highly addictive and are rigorously regulated.

In the context of categories of prohibited drugs, stimulants, depressants, and hallucinogens represent distinct classifications commonly recognized in drug policy and law. Stimulants enhance alertness and energy, depressants reduce arousal and stimulation, and hallucinogens cause significant alterations in perception and consciousness. Each group presents unique risks and potential for abuse.

Therefore, while opioids are indeed a significant concern in public health and law enforcement, they are classified and prohibited under drug regulations. The emphasis in the question is on identifying categories commonly recognized as prohibited drugs, of which opioids is included.