The US Food and Drug Administration (FDA) is fighting, yet again, against “unsubstantiated claims” that marijuana extracts can combat or cure cancer.1 But, while there is a near total lack of clinical evidence to support such therapeutic claims, a raft of preclinical in vivo and in vitro studies suggests that some compounds derived from the plant may have an anti-tumor effect in a variety of cancers — and new clinical and preclinical studies are being developed.

Still, a member of the research team involved in the only known clinical study published to date said that to claim that cannabinoids have anti-cancer powers is, at the very least, premature.

“We cannot say that cannabis cures cancer. I think it’s not responsible to say that,” Guillermo Velasco, PhD, associate professor and researcher in the department of biochemistry and molecular biology at the Complutense University of Madrid in Spain, told Cancer Therapy Advisor. He added, however, that “on the other hand, it’s true that it may work and the first results from clinical studies are promising.”

The FDA recently issued warning letters to yet another group of websites touting the anti-cancer benefits of cannabidiol (CBD). The agency said examples of the claims the 4 companies made included:

  • “Combats tumor and cancer cells;”
  • “CBD makes cancer cells commit ‘suicide’ without killing other cells;”
  • “CBD…[has] anti-proliferative properties that inhibit cell division and growth in certain types of cancer, not allowing the tumor to grow;” and
  • “Non-psychoactive cannabinoids like CBD…may be effective in treating tumors from cancer — including breast cancer.”

It’s hardly the first time the FDA has taken action. In its announcement of the latest warnings, it said it had issued more than 90 such letters in the last 10 years, “including more than a dozen this year” alone.

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The National Cancer Institute (NCI), however, lists several clinical studies of cannabinoids that show variable effectiveness for the treatment of nausea, vomiting, anxiety, appetite loss, and pain associated with cancer therapy.2

Yet the only evidence of antitumor efficacy exists almost exclusively in experimental models.