Which of the following scenarios allows for the sale of dextromethorphan without age restrictions?

The sale of dextromethorphan without age restrictions is permissible when it is dispensed via a prescription. This aligns with regulations that allow certain medications to be provided to patients under the professional judgment of a licensed healthcare provider, regardless of the patient's age. By requiring a prescription, it ensures that a licensed practitioner has evaluated the need for the medication and deemed it appropriate for the patient, thereby bypassing any age-related restrictions that might apply to over-the-counter sales.

In contrast, the other options do not provide the same allowance for unrestricted sale. Selling dextromethorphan during a health fair typically involves over-the-counter transactions, which often adhere to age limits to prevent misuse. Bundling it with other products does not change its regulatory status, and this practice could still be subject to age restrictions. Similarly, making it available on sale doesn’t navigate around the aforementioned regulations, as it still constitutes an over-the-counter purchase. Hence, the most regulation-compliant setting for dispensing dextromethorphan without age limitations is through a prescription.