Which drug is classified as a "depressant" under the Controlled Substances Act?

Methaqualone is classified as a depressant under the Controlled Substances Act due to its effects on the central nervous system, which produce sedation, relaxation, and a decrease in anxiety. As a barbiturate-type sedative, methaqualone works by increasing the effectiveness of the neurotransmitter gamma-aminobutyric acid (GABA) in the brain, leading to a calming effect. This characteristic makes it fall within the category of substances that slow down the body's functions and can impair cognitive and motor skills.

In the context of the other drugs listed, morphine is classified as an opioid and primarily acts as a pain reliever while also being a depressant in certain aspects, but it is specifically categorized under opioids. Cocaine is a stimulant, known for increasing alertness, energy, and attention. Phenmetrazine, similarly, is a stimulant used for weight loss and has effects opposite to depressants, promoting energy and alertness.

Thus, methaqualone is distinctly identified as a depressant, aligning with the criteria set forth in the Controlled Substances Act and highlighting its sedative properties.