Final answer:
A prescription for a CV controlled substance can have a maximum of 5 refills within a 6-month period, as per U.S. federal regulations.
Step-by-step explanation:
Prescriptions for controlled substances are governed by specific regulations. In the case of a Schedule CV prescription, which includes preparations with limited quantities of certain narcotic drugs, the maximum number of refills allowed under U.S. federal law is 5 refills within a 6-month period. It's important to note that the actual number of refills may be less based on the prescriber's discretion or state laws, but it cannot exceed this federal limit.