Which organization is primarily responsible for regulating the safety of drugs in the United States?

The Food and Drug Administration (FDA) is the primary organization responsible for regulating the safety of drugs in the United States. This federal agency is tasked with ensuring that medications are safe and effective before they can be marketed to the public. The FDA oversees the drug approval process, which includes rigorous clinical testing and evaluation of safety and efficacy data submitted by pharmaceutical companies.

Furthermore, the FDA is responsible for monitoring drugs once they are on the market, which includes post-marketing surveillance to identify any adverse effects. By enforcing regulations that govern drug labeling, advertising, and distribution, the FDA plays a critical role in protecting public health.

In contrast, other organizations listed have different primary functions. For instance, the National Institute of Allergy and Infectious Diseases focuses on research related to allergies and infectious diseases, while the Centers for Disease Control and Prevention concentrates on disease prevention and public health response. The National Library of Medicine serves as a repository and resource for biomedical literature and information, rather than directly regulating drugs. Thus, the FDA's specific mandate and established authority in drug regulation make it the correct answer.