WASHINGTON — The Food and Drug Administration said it cannot conclude cannabidiol (C.B.D.) is Generally Recognized As Safe (GRAS) for use in human or animal food, because of a lack of scientific information supporting its safety. The agency said there are “data gaps” about C.B.D. toxicity and some of the available data raise concerns about potential harm.

“We remain concerned that some people wrongly think that the myriad of C.B.D. products on the market, many of which are illegal, have been evaluated by the F.D.A. and determined to be safe, or that trying C.B.D. ‘can’t hurt,’” said Amy Abernathy, Ph.D., principal deputy commissioner for the F.D.A. “Aside from one prescription drug approved to treat two pediatric epilepsy disorders, these products have not been approved by the F.D.A. and we want to be clear that a number of questions remain regarding C.B.D.’s safety — including reports of products containing contaminants, such as pesticides and heavy metals — and there are real risks that need to be considered.

“We recognize the significant public interest in C.B.D. and we must work together with stakeholders and industry to fill in the knowledge gaps about the science, safety and quality of many of these products.”

A revised Consumer Update published by the F.D.A. said “we are aware that there may be some products on the market that add C.B.D. to a food or label C.B.D. as a dietary supplement. Under federal law, it is illegal to market C.B.D. this way.” Specific safety concerns related to C.B.D. products cited include potential liver injury, interactions with other drugs, drowsiness, diarrhea, and changes in mood.

Further, the F.D.A. said studies in animals have shown that C.B.D. can interfere with the development and function of testes and sperm, decrease testosterone levels and impair sexual behavior in males. Questions also remain about cumulative use of C.B.D. and about C.B.D.’s impacts on vulnerable populations such as children and pregnant or breastfeeding women.

The F.D.A. aired its concerns Nov. 25, the same day it sent warning letters to 15 companies selling products containing C.B.D. in ways that violate the Federal Food, Drug and Cosmetic Act (F.D.&C.). One company that received a letter was Organix Industries, San Bernardino, Calif., that the F.D.A. said was selling products such as “classic peanut butter 300 mg C.B.D.,” or “C.B.D. hibiscus tea.”

“As outlined in the warning letters issued today, these particular companies are using product webpages, online stores and social media to market C.B.D. products in interstate commerce in ways that violate the F.D.&C. Act, including marketing C.B.D products to treat diseases or for other therapeutic uses for humans and/or animals,” the F.D.A. said. “Other violations include marketing C.B.D. products as dietary supplements and adding C.B.D. to human and animal foods.”