Which of the following is classified as a Schedule III substance?

The correct answer is Secobarbital suppository, which is classified as a Schedule III substance under the Controlled Substances Act in the United States. Schedule III substances are defined as those that have a potential for abuse less than that of substances classified as Schedule I or II and have accepted medical uses in the U.S. Secobarbital, a barbiturate, is used to treat certain types of sleep disorders but can still lead to physical dependence and abuse.

In contrast, heroin is classified as a Schedule I substance due to its high potential for abuse and lack of accepted medical use. Methaqualone is also a Schedule I substance for similar reasons, as it has no accepted medical use and is known for its high abuse potential. Cocaine, while it has limited medical uses, is classified as a Schedule II substance because of its high potential for abuse and the risk of severe psychological or physical dependence.

Understanding the classifications of these substances is crucial for recognizing the legal implications and medical usage associated with each category. In summary, Secobarbital's classification as Schedule III reflects its controlled yet accepted medical use compared to the other substances listed.