All of the following are controlled substances grouped as stimulants except?

Mescaline is not classified as a stimulant but rather as a psychedelic substance. It is derived from certain cacti and is known for its hallucinogenic effects rather than stimulating activity. In contrast, cocaine, methyphenidate, and amphetamines are all stimulants. Cocaine is a powerful central nervous system stimulant known for its euphoric effects. Methyphenidate is often used in the treatment of attention deficit hyperactivity disorder (ADHD) and works by increasing the levels of certain neurotransmitters in the brain, promoting alertness and focus. Amphetamines are a class of drugs that also significantly enhance alertness and physical activity. Each of these substances, unlike mescaline, primarily increases energy levels and alertness rather than altering perception or consciousness in the way that hallucinogens do.