Frequent cannabis smokers are more prone to bone fractures, a new study has found.

Edinburgh University researchers found people who regularly use the drug have a lower body weight, which can contribute to thinning of their bones.

The study uncovered concerns cannabis smokers are at greater risk of osteoporosis in later life.

Scientists examined 170 people who smoke cannabis regularly for recreational purposes and 114 non-users.

They used a specialised X-ray technique to measure the bone density of each person.

The bone density of cannabis users was about 5% lower than cigarette smokers who did not use the drug.

Fractures were more common in heavy users compared to non-users, while moderate users showed no difference from those who did not take cannabis.

The researchers defined heavy users as those who reported smoking cannabis on 5000 or more occasions.

The average participant in the study had smoked the drug more than 47,000 times, the experts said.

Moderate users had, on average, taken the drug about 1000 times.

The study is the first to investigate bone health among cannabis users.

Researchers say further studies are needed to better understand the link between use of the drug and thinning of bones.

Experts said they were surprised to find frequent cannabis users had a lower body weight and BMI than non-users, as the drug is believed to increase appetite.

They now believe the drug may reduce appetite when it is smoked in large amounts over a long period of time.

The study, funded by Arthritis Research UK, is published in the American Journal of Medicine.

Lead researcher Professor Stuart Ralston, of Edinburgh University's centre for genomic and experimental medicine, said: "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."