Which Schedule V drug is allowed with the least quantity limit?

The correct answer indicating the Schedule V drug with the least quantity limit is linked to the specific regulation surrounding the ingredient codeine in the context of its formulation and concentration.

In the case of Schedule V controlled substances, the regulations state that codeine can be allowed in formulations with a concentration of 200 mg per 100 mL or 100 grams, making this option significant because while it is a relatively low concentration, it allows for a modest quantity in comparison to other opiate substances allowed in Schedule V.

The quantity limits for the other options are higher, making them less favorable in terms of minimal quantity requirements. For instance, formulations containing opium or dihydrocodeine are also permissible under Schedule V, but the higher concentrations of opium and dihydrocodeine per 100 mL or grams allows for potentially larger amounts than the codeine formulation. The inclusion of diphenoxylate with atropine as a directed Schedule V also pertains, but typically, it is relevant for treating diarrhea and has a different regulatory focus not strictly constrained by a quantity limitation that reflects the lesser quantity found in codeine formulations.

Therefore, the significant aspect of codeine's allowance in Schedule V is primarily due to its concentration, establishing it as a