This story is part of a partnership between MedPage Today and VICE News.
A new study claims that a component in cannabis may help heal broken bones, but that doesn't mean you should smoke a joint the next time you find yourself in a cast or on crutches.
Researchers at Tel Aviv University concluded that cannabidiol (CBD), a liquefied non-psychotropic component of the cannabis plant, makes broken bones heal stronger. But their study was small, and it wasn't in humans; it was in a couple dozen rats.
The results are preliminary at best, experts say.
"Insofar as these studies go, it's not the worst I've seen, but the numbers are, I would say, on the low side," said Jeffrey Nyman, PhD, of the Vanderbilt Center for Bone Biology.
The study was published in the Journal of Bone and Mineral Research and has generated such pun-tastic headlines as "No Bones About It: Cannabis May Be Used to Treat Fractures" and "Joint Relief: Marijuana Helps Mend Broken Bones."
But lead study author Yankel Gabet, DMD, PhD, of Tel Aviv University, said it's not clear how CBD heals bones in rats, let alone whether it would work in humans.
"The main limitation is that this is the very first study on the matter and results have been obtained in animals only," Gabet told VICE News/Med Page Today.
Gabet and his team methodically broke the rats' femurs and administered THC, CBD, or an ethanol/emulphor/saline solution that served as a control to see how well the rats' bones healed over eight weeks using 3D micro-computed tomography and biomechanical machines. As part of a second experiment, they tried a mixture of THC and CBD, THC alone, and CBD alone. The third experiment in the study involved measuring how THC and CBD affected the enzymes that prompt collagen cross-linking in healing bones, and the researchers reported that CBD enhanced expression of the enzyme lysyl hydroxylase 1, or PLOD 1.
"It would be a big leap to then conclude that CBD in a person, at a certain dose or used in a certain way, will help their bones heal."
Each group had between five and 12 rats, which Nyman said was not ideal. And after the eight weeks were up, Gabet and his team euthanized the rats, removed the once-broken femurs and studied them after first coating them in formalin, dehydrating and rehydrating them.
Dr. Margaret Gedde, who has treated only medical marijuana patients since 2009 at her practice in Colorado, said Gabet's study is a good example of a basic animal study to pave the way for an eventual human study, but it's not enough to draw conclusions for the future of fracture care.
"It would be a big leap to then conclude that CBD in a person, at a certain dose or used in a certain way, will help their bones heal," she said. "Animals are not people. But the study does lay new ground and points to the possibility that CBD in some form might be used to help bone healing in people."
Dr. Robert Glatter, who directs the emergency sports medicine program at Lenox Hill Hospital in New York City, expressed similar sentiments.
"Whether it translates to humans is unclear," Glatter said. "It's going to require much more work with multiple studies…. That said, it's encouraging."
Glatter says he expects it will be another five or 10 years before doctors have CBD on hand to treat fracture patients in the ER — assuming CBD proves itself in human studies.
Nyman said he'd take the study with a grain of salt because of its small size and the fact that the researchers did something unusual: After euthanizing the animals and extracting the healed femurs, the researchers coated those femurs with formalin, a preservative. (They did not say how diluted it was.) Then they dehydrated and rehydrated the femurs before examining them, measuring the callusing as well as strength.
The formalin may have helped produce some of the bone-strengthening collagen cross-linking the researchers were attributing to the CBD, Nyman said. Even though this was done for all test subjects, he said the study was too small to say whether the formalin affected them equally and didn't change the study outcome.
Furthermore, instead of making the rats' bones heal faster, as many headlines are suggesting, the researchers found that rats given CBD actually healed slower than the others by four weeks after the fracture, and then caught up.
"It's very clear to me that this is not accelerated healing," Nyman said.
Gabet and his team said that while they didn't measure long-term effects, previous studies have shown CBD to be safe.
"Implicating PLOD 1 in the mechanism of action of CBD may have far-reaching significances, beyond the improvement of fracture healing, in instances such as Ehlers-Danlos syndrome, bronchopulmonary dysplasia, bicuspid aortic wall-associated aneurisms, and cancer metastases," wrote the authors, who included the so-called "grandfather of marijuana," Raphael Mechoulam, PhD. Decades ago, Mechoulam, now a medicinal chemist at the Hebrew University of Jerusalem, was the first to identify THC in cannabis.
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