To date, human work assessing the effects of phytocannabinoids on indicators of bone health has been limited to epidemiological data,^26,27 and only one previous human study explored bone turnover markers associated with cannabis use. In a cross-sectional study, both CTx and P1NP were elevated in heavy cannabis users as compared with a cigarette-smoking control group.²⁶ As exact cannabis product composition and frequency/duration of use could not be controlled, the association of specific phytocannabinoids or cannabis products with bone turnover markers has not yet been established.

In our study, participants were randomized to receive one of four doses of Spectrum Yellow oil (120–480 mg CBD and 5.4–21.6 mg THC daily) or Spectrum Red softgels (0.06–0.24 mg CBD and 5–20 mg THC daily), two well characterized commercially available cannabis products. The studied dosages of THC and CBD were based on the primary aim of the parent trials to evaluate the safety, pharmacokinetics, and pharmacodynamics of THC and CBD. This large dose range was intended to closely approximate real-world conditions in individuals who consume cannabis for medical purposes and to best inform physician and patient decision-making regarding a variety of dosing parameters. Future studies with lower dosages of THC and CBD will be more relevant for individuals who consume cannabis for nonmedical purposes. Owing to sample size restrictions, we were not able to compare CBD and/or THC dose level within treatments with bone marker changes. That both Spectrum Yellow and Red products were found to produce an equal attenuation of CTx may be an indication that both CBD and THC act on this biomarker but may also be confounded by the presence of both cannabinoids, although at different concentrations, in both study products.

Sex differences in cannabinoid function, pharmacology, and receptor distribution have been noted in pre-clinical literature,^39–41 and bone marker expression and bone disease risk are known to differ between men and women across different age groups.^42–48 This study recruited both male and female participants but was not designed to examine differences in bone marker response between sexes. In agreement with previous literature,^42,43 we observed higher baseline levels of all three bone markers in this healthy population. However, the overall response to cannabinoid products followed a similar pattern in men and women. Whether this uniform effect across sexes is maintained in patient populations exhibiting bone-specific conditions is unknown.

Bone markers, particularly markers of resorption, are known to follow a diurnal rhythm.^49,50 Peak levels of serum CTx have been shown to occur in the early morning (05:00–08:00 hours), with nadir in the early afternoon (14:00 hours), rising again by late afternoon (17:00 hours). Across treatments, we observed higher CTx on day 8 (mean collection time=16:39 hours) as compared with days −1 (13:20 hours) and 13 (11:06 hours). Collection time variation may also explain the prevalence of findings outside RR, because RR is established following optimal (morning, fasted) serum collection procedures. As bone markers were an exploratory endpoint in the original study design, serum collection times were not optimized for CTx measurement.

Future work in this area should ensure serum collection is standardized across participants, occurring in the morning following an overnight fast, as fasting significantly reduces individual diurnal variations.⁵¹ Of importance, in this study, time of serum collection was uniform between treatments at each timepoint. Differences in CTx between participants receiving cannabis products versus placebo on day 8 are therefore expected to be owing to the products themselves, rather than serum collection timing. Bone turnover markers are also known to be affected by age, BMI, recent fracture, tobacco/alcohol intake, and in women, phase of the menstrual cycle, pregnancy, lactation, and menopausal status.^52–58

Within person variation in the Australian population is estimated at 8% (ALP and P1NP) to 10% (CTx), whereas clinically relevant least significant change (LSC) in CTx and P1NP during antiresorptive treatment is generally defined as 2.8 times the biological variation (∼30% and ∼21%, respectively).⁵⁹ Although not an ideal comparison, we observed a difference of −24.2% (Spectrum Yellow) and −24.6% (Spectrum Red) when oral medical cannabis products were compared with placebo treatment over a 7-day dosing period. This finding is in line with pre-clinical work, which has demonstrated ∼18% decrease in CTx following repeated CBD dosing (10 mg/kg) in healthy male mice over 8 weeks.¹³ Whether longer dosing duration and/or treatment of populations with elevated bone turnover would further attenuate CTx levels or modulate bone formation markers above LSC remains to be established.

Total ALP has been shown to be elevated in rodents and dogs,^60–63 but uncommonly in humans,^64,65 following repeated administration of cannabinoids, particularly CBD. In agreement with existing human data, cannabinoid administration did not result in ALP elevation in this study. Although ALP activity is often associated with liver function, serum ALP also originates from several other tissues, including bone (∼50% of total ALP).³⁰ Total ALP activity has traditionally been used as a therapeutic marker in multiple bone conditions,⁶⁶ but tissue-specific isoform assays have become available. Future work should evaluate activity of the bone-specific ALP isoform, which is more directly correlated with the number and differentiation state of osteoblasts.⁶⁷

This is the first interventional human study to explore the effect of cannabinoids on biomarkers of bone turnover. In healthy adults, short-term treatment with commercially available medical cannabis products, Spectrum Yellow oil and Spectrum Red softgels, did not result in clinically significant changes in bone turnover markers. However, as compared with placebo treatment, oral medical cannabis products attenuated the increase in a resorption marker, CTx, following 7 days of twice daily administration. This finding may be indicative of protective properties of cannabinoids in bone. Further research following longer term treatment in individuals exhibiting bone-specific risk factors and/or medical conditions (e.g., osteopenia, osteoporosis) is warranted.