Which organization is involved in issuing registration to practitioners for controlled substances?

The Drug Enforcement Administration (DEA) is the correct organization involved in issuing registrations to practitioners for controlled substances. The DEA regulates the manufacture, distribution, and dispensing of controlled substances in the United States to ensure that these drugs are used safely and appropriately. Practitioners who wish to prescribe, dispense, or administer these controlled substances must register with the DEA and comply with its regulations. The registration process helps maintain oversight over the use of narcotics and dangerous drugs to prevent misuse and ensure public safety.

The Food and Drug Administration (FDA) primarily focuses on the safety and efficacy of drugs, but it does not issue registration for practitioners to handle controlled substances. The Centers for Disease Control and Prevention (CDC) is concerned with public health issues, including disease control and prevention, rather than the licensing of drug practitioners. The National Institutes of Health (NIH) conducts and supports medical research but does not have a role in issuing registrations for controlled substances. Therefore, the DEA's specific function in this area establishes it as the correct answer.