The Food and Drug Administration has become more active in regulating cannabidiol (C.B.D.) products. The agency sent warning letters dated March 28 to three companies marketing C.B.D. products with “egregious and unfounded claims that are aimed at vulnerable populations,” the agency said. The F.D.A. also has scheduled a May 31 public hearing to discuss how C.B.D. products may be marketed legally. “As our actions today make clear, the F.D.A. stands ready to protect consumers from companies illegally selling C.B.D. products that claim to prevent, diagnose, treat or cure serious diseases, such as cancer, Alzheimer’s disease, psychiatric disorders and diabetes,” said Scott Gottlieb, M.D., commissioner of the F.D.A “The agency has and will continue to monitor the marketplace and take enforcement action as needed to protect the public health against companies illegally selling cannabis and cannabis-derived products that can put consumers at risk and are being marketed and distributed in violation of the F.D.A.’s authorities.”