Final answer:
An inventory of controlled substances must be taken biennially as per DEA regulations to prevent diversion and ensure accurate record-keeping.
Step-by-step explanation:
The correct answer to the question "How often must an inventory of controlled substances be taken?" is d) Biennially. According to the United States Drug Enforcement Administration (DEA), entities that are registered with the DEA must take an inventory of all stocks of controlled substances every two years.
This is a regulatory requirement designed to prevent the diversion of controlled substances for illegal purposes.
Businesses that handle controlled substances must maintain accurate records that detail every transaction. This biennial inventory involves counting stocks of controlled substances and maintaining records that satisfy DEA requirements.
Failure to conduct a biennial inventory can result in penalties and loss of license to handle controlled substances.