Which of the following is NOT considered an upper?

Heroin is classified as an opioid and is considered a depressant rather than a stimulant or "upper." It acts on the central nervous system to produce effects such as pain relief, sedation, and euphoria, which are characteristic of depressants. In contrast, substances like caffeine, methamphetamines, and PCP/LSD are known for their stimulating effects on the brain, increasing alertness, energy, and sometimes causing hallucinogenic effects. This distinction is important for understanding the pharmacological categories of these substances and their effects on the body and mental state.