Final answer:
Under the CSA, DEA registration numbers are necessary primarily for controlled substances prescriptions. For non-controlled substances, it is not required but may be requested. Including a DEA number can help prevent fraud and abuse in all prescriptions.
Step-by-step explanation:
The Controlled Substances Act (CSA) requires DEA registration numbers for prescriptions written for controlled substances. For non-controlled substances, it is not a federal legal requirement to include a DEA number; however, pharmacists may still request it for verification purposes. The DEA number is primarily used to track controlled substance transactions, but it can be included on all prescriptions to help prevent fraud and abuse. It's important for medical professionals to adhere to both federal and state regulations when prescribing medication.