Which product listed would be classified as a Schedule III controlled substance?

A product that contains 15 mg of hydrocodone per dose is classified as a Schedule III controlled substance because hydrocodone is an opioid that, when combined with other medications, falls under this schedule due to its potential for abuse and dependence but is considered to have lower risk compared to Schedule II substances. The classification occurs because the strength and combination of hydrocodone, when not exceeding specific limits, results in a drug that is medically useful while still posing a possibility of misuse.

In the case of products containing codeine, products must contain less than 90 mg of codeine in a dosage unit to be classified under Schedule III, which limits them to specific combinations or lower doses. Diphenoxylate is usually classified as a Schedule V controlled substance unless certain concentrations are combined with atropine. Tramadol, while also an opioid, is generally classified under similar but separate guidelines, and its use leads to more stringent regulations compared to hydrocodone when produced in higher concentrations or in certain forms. Therefore, the selected option clearly aligns with the definitions and classifications recognized in drug regulatory guidelines.