Now researchers at the University of California, Irvine, think they know why—and no, pot consumption isn’t the secret to a svelte figure.

Not a healthy one, anyway.

Frequent cannabis consumers are leaner and less likely to develop type two diabetes. But the pseudo-health benefit comes at a price, researchers assert in a June 2 article published in Cell Metabolism.

Many cannabis consumers begin use during their teenage years. Realizing this, researchers gave low doses of THC—tetrahydrocannabinol, the main psychoactive component of marijuana—to adolescent mice. Once the mice were fully grown, they stopped the doses, but the damage was done. 

Drug-free male mice that had consumed THC as “teens” had reduced fat mass, increased lean mass, had higher-than-average body temperatures, and were partially resistant to both obesity and hyperglycemia. They were in what researchers referred to as a “pseudo-lean” state. 

But they also had a reduced ability to use fuel from fat stores—a consequence that can interfere with tasks like moving and thinking, and especially sustaining attention, researchers found.

Similar features are seen in some humans who are frequent cannabis users, they remarked.

“All too often we think of cannabis only as a psychoactive drug,” said Daniele Piomelli—one of the study’s authors, director for the university’s Center for the Study of Cannabis, and professor in its School of Medicine Department of Anatomy & Neurobiology—in a news release on the study. “But its effects extend well beyond the brain.”

The reason for these permanent changes surprised the study’s authors. Once exposed to THC, fat in the mice’s stores began making proteins normally found only in the muscle and the heart. Meanwhile, their muscle cells begin making fewer of the proteins they should. The effort required of fat cells to make these “alien” proteins interferes with the correct, healthy functioning of fat cells, and their ability to store and release nutrients, researchers concluded.

It’s well established that cannabis consumption is linked to lower BMI and improved cardiometabolic risk, the authors write. But their findings point to the ability of the drug to permanently disrupt organ function, “with potentially far-reaching consequences on physical and mental health,” Piomelli said.

“Adolescent exposure to THC may promote an enduring ‘pseudo-lean’ state that superficially resembles healthy leanness but might, in fact, be rooted in … organ dysfunction,” the authors wrote.

These same changes aren’t thought to occur in cannabis users who begin using during adulthood, they added.

The study found that THC use in adolescent mice resulted in reduced weight gain in both males and females. But the study only focused on metabolic and molecular effects in males, the authors wrote, noting that similar studies should be conducted on females. 

Similarly, further studies should look at other organ systems for potential THC-driven changes, they added.