Which of the following substances would be classified as a depressant under the Controlled Substance Act?

The correct choice is Miltown, which is classified as a depressant under the Controlled Substance Act. Miltown, known by its generic name meprobamate, acts as an anxiolytic and muscle relaxant that depresses the central nervous system. By binding to specific sites in the brain, it reduces anxiety and induces a calming effect, characteristic of depressant substances.

Other choices, while related to the field of pharmaceuticals, include substances that have different classifications. Preludin, for instance, is an amphetamine derivative known for its stimulant effects, particularly in enhancing alertness and reducing fatigue. Darvon, or propoxyphene, is an opioid analgesic, classified primarily due to its pain-relieving properties rather than as a depressant. Dilaudid, with its active ingredient hydromorphone, is a strong opioid narcotic used for pain management and has significant depressant effects, but it is primarily categorized under opioid substances rather than general depressants.

Understanding these classifications is crucial, as it impacts how substances are regulated and prescribed, particularly in contexts involving substance use and abuse.