What additional information about controlled substances must be retained for two years?

The correct choice highlights the importance of maintaining detailed records about the quantity and kind of each controlled substance. Under state and federal regulations, pharmacies are required to keep accurate inventory records of controlled substances to prevent misuse and ensure accountability. This includes tracking how much of each controlled substance is received, dispensed, or otherwise handled.

Maintaining this data for at least two years is critical for compliance with the law. It allows authorities to verify that substances are being managed appropriately and helps in audits and inspections. This practice also serves a vital role in addressing issues such as diversion or theft of controlled substances, ensuring that health care professionals uphold the integrity of their practice.

Other options, while potentially important in their own right, do not specifically pertain to the legal requirements for controlled substances inventory retention. Employee training data, sales reports, invoices, and supplier contracts may be relevant for overall operations or financial management but are not specifically mandated to be retained for the same duration as the records concerning controlled substances.