WASHINGTON — Cannabis stocks took a hit on Tuesday, after the Food and Drug Administration issued new guidance on CBD.

In a revised consumer update released on Monday, the FDA emphasized that it’s currently illegal to market CBD by adding it to a food or labeling it as a dietary supplement. The agency said it can’t conclude that CBD is “generally recognized as safe” (GRAS) by qualified experts for use in human or animal food. In addition, the FDA pointed out that CBD products marketed for therapeutic uses, including topicals, haven’t been approved, and their claims and safety remain uncertain.

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

“And there are real risks that need to be considered,” she added. “We recognize the significant public interest in CBD, 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.”

The FDA issued warning letters to 15 companies for illegally selling products containing CBD in ways that violate the Federal Food, Drug and Cosmetic Act (FD&C Act). Companies receiving the warnings included Koi CBD, Pink Collections, Noli Oil, Natural Native, Whole Leaf Organics, Infinite Product Co. (dba Infinite CBD), Apex Hemp Oil, Bella Rose Labs, Sunflora Inc. (dba Your CBD Store), Healthy Hemp Strategies (dba Curapure), Private I Salon, Organix Industries (dba Plant Organix), Red Pill Medical, Sabai Ventures and Daddy Burt (dba Daddy Burt Hemp Co.).

“CBD is marketed in a variety of product types, such as oil drops, capsules, syrups, food products such as chocolate bars and teas, and topical lotions and creams,” the FDA said in a statement. “As outlined in the warning letters issued today, these particular companies are using product Web pages, online stores and social media to market CBD products in interstate commerce in ways that violate the FD&C Act, including marketing CBD products to treat diseases or for other therapeutic uses for humans and/or animals. Other violations include marketing CBD products as dietary supplements and adding CBD to human and animal foods.”

Under the FD&C Act, the FDA defines a drug as any product intended to treat a disease or have a therapeutic or medical use, as well as any product — other than a food — intended to affect the structure or function of the body of humans or animals. The FDA noted that, unlike drugs approved by the agency, it hasn’t evaluated whether these CBD products are effective for their intended use, what the proper dosage might be, how they might interact with FDA-approved drugs, or whether they have dangerous side effects or other safety concerns. In addition, the manufacturing process of unapproved CBD drug products hasn’t been subject to FDA ­review.