Scientists studied the impact of cannabis on the bones
Researchers looking at the effects of cannabis on bones have found its impact varies dramatically with age.
The study found that while the drug may reduce bone strength in the young, it could protect against osteoporosis, a weakening of the bones, in later life.
The results were uncovered by a team at the University of Edinburgh who compared the drug's effects on mice.
Osteoporosis affects up to 30% of women and about 12% of men at some point in their lives.
The group found that cannabis can activate a molecule found naturally in the body that is key to the development of osteoporosis.
When the type 1 cannabinoid receptor (CB1) comes into contact with cannabis, it has an impact on bone regeneration.
However, until now, it was not clear whether the drug had a positive or negative effect.
Researchers, funded by the Arthritis Research Campaign, investigated this using mice which lacked the CB1 receptor.
The scientists then used compounds - similar to those in cannabis - that activated the CB1 receptor.
They found that compounds increased the rate at which bone tissue was destroyed in the young.
Despite this, the study also showed that the same compounds decreased bone loss in older mice and prevented the accumulation of fat in the bones, which is known to occur in humans with osteoporosis.
Stuart Ralston, the Arthritis Research Campaign Professor of Rheumatology at the University of Edinburgh, who led the study, said: "This is an exciting step forward, but we must recognise that these are early results and more tests are needed on the effects of cannabis in humans to determine how the effects differ with age in people.
"We plan to conduct further trials soon and hope the results will help to deliver new treatments that will be of value in the fight against osteoporosis."
The results are published in Cell Metabolism.