Which of the following is considered a controlled substance?

Diazepam is classified as a controlled substance due to its potential for abuse, dependency, and addiction. It is part of the benzodiazepine class of medications, which are commonly prescribed for anxiety, muscle spasms, and seizures but can also lead to significant sedative and euphoric effects. Because of these characteristics, diazepam is regulated under controlled substance laws, which dictate how it can be prescribed, dispensed, and documented.

In contrast, ibuprofen, amoxicillin, and levothyroxine do not fall under this classification. Ibuprofen is a nonsteroidal anti-inflammatory drug (NSAID) used for pain relief and inflammation and does not have significant abuse potential. Amoxicillin is an antibiotic used to treat bacterial infections and is not controlled due to its low risk of misuse. Levothyroxine is a hormone replacement therapy for hypothyroidism, and it also lacks the characteristics that typically necessitate control.