Which of the following substances is classified as an opioid?

Heroin is classified as an opioid because it is derived from morphine, a natural substance obtained from the opium poppy. Opioids are a class of drugs that include both legal prescription medications, such as oxycodone and morphine, as well as illegal substances like heroin. They work by binding to specific receptors in the brain and body to produce pain relief, euphoria, and sedation.

In contrast, cocaine is a stimulant that affects the central nervous system and produces different effects such as increased energy and alertness. Alcohol is a depressant that impacts the brain’s neurotransmitter systems but does not belong to the opioid category. Nicotine, found in tobacco products, is also a stimulant and does not have the pain-relieving properties associated with opioids. Thus, only heroin from the given choices is recognized as an opioid due to its origin and its mechanism of action in the body.