While marijuana remains the most commonly used illicit drug in the United States, it is becoming increasingly legalized, making it more important than ever to identify the potential harms of the drug. Now, a new study finds that regular, heavy marijuana use may reduce bone density, increasing the risk of osteoporosis and bone fractures.

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Researchers found heavy marijuana use was linked to a reduction in bone density.

According to the National Institute on Drug Abuse (NIDA), a 2014 survey identified around 22.2 million past-month marijuana users, with use of the drug highest among teenagers and young adults.

To date, 25 U.S. states and Washington, D.C., have legalized marijuana for medical and/or recreational purposes, and this number is expected to rise.

While such legalization is welcomed by many, others have raised concerns that it will lead to a dramatic rise in recreational use of the drug, exposing more individuals to its possible health risks.

As such, there has been increasing focus on identifying such risks; recent studies have suggested the drug may impair blood vessel function and increase the risk of periodontal disease.

Now, a new study – published in the American Journal of Medicine – suggests poorer bone health can be added to the list.

The research team – led by Prof. Stuart Ralston of the Centre for Genomic and Experimental Medicine at the University of Edinburgh in the United Kingdom – analyzed the data of 284 adults who attended primary care centers in the U.K. between 2011-2013.

Of these adults, 170 used marijuana regularly for recreational purposes, while 114 adults were cigarette smokers who did not use marijuana.

For the study, the researchers classed heavy marijuana use as smoking the drug more than 5,000 times over a lifetime. However, on average, heavy users in the study had smoked marijuana more than 47,000 times throughout their lifetime, while moderate users had smoked it around 1,000 times.

Using an X-ray method known as dual energy X-ray absorptiometry (DEXA), the researchers measured participants’ bone mineral density.

Compared with non-users, the researchers found heavy marijuana users had a 5 percent lower bone density, which the team says may raise the risk of bone-related health problems.

We have known for a while that the components of cannabis can affect bone cell function, but we had no idea up until now of what this might mean to people who use cannabis on a regular basis.

Our research has shown that heavy users of cannabis have quite a large reduction in bone density compared with non-users, and there is a real concern that this may put them at increased risk of developing osteoporosis and fractures later in life.”

Prof. Stuart Ralston

On further investigation, the researchers found that heavy marijuana users had a lower body weight and body mass index (BMI) than non-users – factors that are associated with bone thinning.

This finding, they say, might explain the observed reduction in bone density with heavy marijuana use, though they stress that more research is required to understand this association.

Read about a study that suggests marijuana is a better pain reliever for men than women.