How does cannabis affect bone health and fracture healing?

Bone metabolism is regulated by the ECS — osteoblasts (bone-forming cells) and osteoclasts (bone-resorbing cells) both express CB1 and CB2 receptors. The effects are complex and receptor-dependent. CB2 stimulation: promotes osteoblast activity and inhibits osteoclast activity — net bone-building effect. Animal studies show CB2 agonists increase bone density and accelerate fracture healing. A 2015 study found CBD accelerated fracture healing in rats and improved bone strength. CB1 stimulation: more complex — CB1 on sympathetic nerve terminals in bone regulates bone remodeling; chronic CB1 activation may reduce bone density. Epidemiological data: some studies show cannabis users have lower bone density and higher fracture risk, but confounding (tobacco use, lower BMI, falls risk) makes interpretation difficult. A 2017 study found cannabis users had lower bone density and higher fracture risk, but this was attenuated after controlling for tobacco use. Clinical bottom line: topical or systemic CB2-selective agonists may have bone-protective effects; chronic THC use may have modest negative effects on bone density.