What must be included in all controlled substance prescriptions for it to be considered valid?

For a prescription for a controlled substance to be considered valid, it is essential for the prescriber’s DEA registration number to be included. This requirement is in place to ensure that the prescriber is authorized to prescribe controlled substances. The DEA registration number verifies the legitimacy of the prescriber’s authority and helps in tracking prescriptions for controlled substances, which are subject to stricter regulations due to their potential for abuse and dependency. Including this number on the prescription provides a safeguard against illegal prescribing and helps maintain the integrity of controlled substance management.

The other options do not meet the legal requirements for a valid prescription. For instance, while a patient’s insurance information might be helpful for billing purposes, it is not necessary for the validity of the prescription itself. Similarly, checks for previous medications prescribed are part of good clinical practice, but they aren't required elements for a prescription to be valid. Witness signatures are neither relevant nor required for prescriptions, as the phrasing suggests a misunderstanding of the process of prescribing controlled substances.