The companies sell CBD over the internet in a wide range of oil drops, capsules, syrups, teas and creams. The websites feature endorsements from people — generally identified only by first names and last initials — who claim that they or their loved ones have been miraculously cured of terminal diseases and other illnesses.
“There are a growing number of effective therapies for many cancers,” said Dr. Gottlieb, a cancer survivor himself. “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 save lives.”
Stanley Brothers, a leading marijuana product company based in Colorado, notes on its website that other cannabis companies have also gotten F.D.A. warning letters. As of Wednesday afternoon, there were no references to its products as cancer cures on the website.
Dara Kaplan, a spokeswoman for CW Hemp, one of the names under which Stanley Brothers operates, said the company would work with the F.D.A. to better monitor third-party testimonials. “We take regulatory compliance very seriously,” Ms. Kaplan said.
But the F.D.A. also took issue with a previous claims for the company’s Everyday Advanced Hemp Oil. One testimonial said: “A patient of mine uses this for cancer and it gives lots better relief than prescription drugs!’’
“My dear ex-mother-in-law has been diagnosed with late stage pancreatic cancer,” said another testimonial. “This is the only thing that gives her relief.”
The F.D.A. said that other claims on the website of the company’s affiliated nonprofit group, called Realm of Caring, show that Stanley Brothers recommends using its products as drugs, which would require the company to go through the normal drug approval process.
John Hudak, a senior fellow at the Brookings Institution and the author of “Marijuana: A Short History,” said companies that sell traditional cannabis products and those derived from hemp often skirt the edges of the law or violate it outright.
“I think it’s a very difficult argument to say that they are not working in a way that is in violation of F.D.A. standards and practices,’’ Mr. Hudak said. “Having one disclaimer on a website and then having other claims elsewhere on a website is not what the F.D.A. allows.”
The businesses have 15 days to submit evidence to the F.D.A. that they have corrected the violations or to explain why more time is needed.
Tisha Casida, the chief executive of That’s Natural, which markets CBD All-Natural Hemp Oil, said she would comply with the F.D.A.’s request, albeit under protest. One of the company’s claims, according to the F.D.A., was that the hemp oil contained an ingredient that “makes cancer cells commit suicide.’’
“All free people have a right to experience health and wellness from naturally derived cannabinoids,” she wrote in an email. ‘‘We should not have to only take F.D.A.-approved synthesized drugs. We should be able to experience natural plant-based medicine in its truest form.’’
Some of the other companies did not respond to requests for comment.