Which of the following is NOT considered an opioid?

Amphetamines are classified as stimulant drugs, primarily affecting the central nervous system to increase alertness, attention, and energy by enhancing the activity of certain neurotransmitters. In contrast, heroin, codeine, and morphine are all members of the opioid class, which are derived from the opium poppy and primarily used for pain relief. Opioids work by binding to specific receptors in the brain and spinal cord, leading to decreased perception of pain and altered emotional response to pain. Since amphetamines do not share these properties or classifications, they are the correct answer to this question.