The Food and Drug Administration on Wednesday publicly scolded and threatened companies claiming that marijuana-based products could treat or cure cancer.

In the harshly worded announcement, the agency suggested that the “deceptive marketing” was tantamount to “health fraud” and that the agency was “increasingly concerned at the proliferation of products claiming to treat or cure serious diseases like cancer.”

The FDA called out four companies in particular during the tongue-lashing. The agency alleges that they were making illegal and unproven health claims about products containing the marijuana component cannabidiol (CBD). The companies—Greenroads Health, Natural Alchemist, That’s Natural! Marketing and Consulting, and Stanley Brothers Social Enterprises LLC—collectively marketed more than 25 CBD-containing products as being able to reverse, prevent, and/or cure various types of cancers, according to the agency.

The FDA also released warning letters it had sent to the companies, listing their individual violations. Among them were claims on websites, online stores, and social media that a given product:

“Combats tumor and cancer cells”

“makes cancer cells commit ‘suicide’ without killing other cells”

“[has] anti-proliferative properties that inhibit cell division and growth in certain types of cancer, not allowing the tumor to grow”

“may be effective in treating tumors from cancer—including breast cancer”

In a statement, FDA Commissioner Scott Gottlieb, said:

Substances that contain components of marijuana will be treated like any other products that make unproven claims to shrink cancer tumors. We don’t let companies market products that deliberately prey on sick people with baseless claims that their substance can shrink or cure cancer and we’re not going to look the other way on enforcing these principles when it comes to marijuana-containing products… There are a growing number of effective therapies for many cancers. When people are allowed to illegally market agents that deliver no established benefit they may steer patients away from products that have proven, anti-tumor effects that could extend lives.

Baked claims

A massive report released this year by the National Academies of Science, Engineering, and Medicine concluded that there is no or insufficient evidence linking cannabis use to cancer prevention . And there is no clinical evidence that marijuana—or its components—can treat cancers. (There are two FDA-approved cannabinoid drugs to treat nausea from chemotherapies, though.)

The companies were likely basing their health claims on a small number of animal and cell studies suggesting that CBD and other marijuana components may be able to damage or kill cancer cells. For example, a 2011 study suggested that CBD could inhibit breast cancer cell growth and reduce the size of lung cancer tumors in mice. As the National Cancer Institute notes, other rodent studies have found that CBD may work synergistically with chemotherapy drugs.

However, these findings are preliminary, far from being validated or clinically relevant. And mouse studies are notoriously bad at predicting the success of potential treatments in humans.

Beyond a complete lack of data showing the products work in humans, the FDA also notes that there is no data on proper dosages or how they may interact with other drugs.

Further Reading Does biomedical research have a mouse addiction?

“We recognize that there’s interest in developing therapies from marijuana and its components, but the safest way for this to occur is through the drug approval process—not through unsubstantiated claims made on a website,” Gottlieb said. “We support sound, scientifically-based research using components derived from marijuana, and we’ll continue to work with product developers who are interested in bringing safe, effective, and quality products to market.”

The companies have 15 days to address the FDA’s concerns. Failure to do so, the agency warned, “may result in legal action, including product seizure and injunction.”

Some of the companies told The New York Times that they would work with the agency to make sure they were in compliance—but some did so begrudgingly.

Tisha Casida, the chief executive of That’s Natural, which markets CBD All-Natural Hemp Oil, told the Times in an e-mail: