A randomized, double-blinded, placebo-controlled crossover pilot study of oral cannabidiol oil as adjunctive treatment for osteoarthritis-associated pain in dogs

Technical Summary: A Randomized, Double-Blinded, Placebo-Controlled Crossover Pilot Study of Oral Cannabidiol Oil in Dogs with Osteoarthritis

Problem Statement
Osteoarthritis (OA) is a prevalent, degenerative condition in dogs causing chronic pain and reduced quality of life. While nonsteroidal anti-inflammatory drugs (NSAIDs) are standard care, long-term use is limited by side effects, particularly in dogs with comorbidities. Cannabidiol (CBD) oil has emerged as a potential adjunctive therapy for pain management, yet clinical data regarding its efficacy using validated pain outcome measures remains limited. Furthermore, existing literature exhibits significant heterogeneity in study design, dosage, and washout periods. Specifically, previous crossover trials have not consistently utilized a washout period sufficient to eliminate potential carryover effects, given the pharmacokinetic profile of CBD in dogs (elimination half-life ~4.2 hours) and evidence suggesting persistent effects may last up to four weeks. There is a lack of pilot data utilizing a rigorous 4-week washout to inform the design of adequately powered future clinical trials.

Methodology
This study was a prospective, randomized, double-blinded, placebo-controlled crossover pilot trial involving ten client-owned dogs with radiographically confirmed OA.

• Study Design: The trial spanned 12 weeks, consisting of three 4-week phases: a treatment phase (either CBD oil or placebo), a 4-week washout period, and a second treatment phase (the alternative intervention). Each dog served as its own control.
• Interventions:
  • CBD Oil: Administered orally at 2 mg/kg twice daily. The product was a broad-spectrum, cold-pressed hemp oil containing 93.25 mg/ml of total CBD and CBDa, mixed with salmon oil.
  • Placebo: A vehicle control consisting of cold-pressed hemp seed oil (to mimic smell and consistency) mixed with salmon oil, containing no cannabinoids.
• Inclusion/Exclusion: Dogs were included if they had OA in one or more joints, were not surgical candidates, and showed signs of pain. Dogs on stable analgesic regimens (e.g., NSAIDs, gabapentin) were permitted to continue them unchanged to maintain ethical standards and reflect real-world clinical practice.
• Outcome Measures: Pain and OA severity were assessed using three validated Clinical Metrology Instruments (CMIs) at four time points (baseline, post-phase 1, post-washout, post-phase 2):
  1. Helsinki Chronic Pain Index (HCPI): A 11-item owner-reported questionnaire.
  2. Liverpool Osteoarthritis in Dogs (LOAD): A 13-item owner-reported questionnaire.
  3. Canine Osteoarthritis Staging Tool (COAST/COASTeR): A veterinary assessment tool incorporating orthopedic examination and radiographic findings (COAST) or excluding radiographic components (COASTeR).
• Statistical Analysis: As an exploratory pilot, no formal hypothesis testing was performed. Data were summarized descriptively using medians and interquartile ranges (IQR). Within-dog paired differences were calculated to estimate effect sizes (Cohen's dz) for power analysis in future studies.

Key Results

• Efficacy: Changes in pain-related outcome scores were modest and variable.
  • Veterinary Assessments (COAST/COASTeR): Scores remained largely stable across all phases. Median changes between CBD and baseline, or CBD and placebo, were negligible (e.g., median change of 0 for COASTeR).
  • Owner-Reported Assessments (HCPI/LOAD): These scales demonstrated greater within-dog variability compared to veterinary assessments. While median HCPI and LOAD scores showed some reduction after CBD administration relative to baseline, the variability was high (e.g., HCPI median change of -0.5 with an IQR of 9.5). Notably, scores tended to increase (worsen) during the placebo and washout phases relative to baseline in some comparisons.
• Safety: The treatment was well-tolerated. One dog experienced mild, self-limiting diarrhea and vomiting during both the CBD and placebo phases, suggesting these events were not specifically attributable to CBD. No other clinically relevant adverse effects were observed.
• Power Analysis: Post-hoc power analysis based on the pilot data indicated that future studies would require significantly larger sample sizes to detect effects of the magnitude observed. Estimated requirements ranged from 24 to 132 dogs, depending on the specific outcome measure (HCPI requiring fewer subjects than LOAD) and the desired statistical power (80% vs. 90%).

Significance and Claims
The authors position this study primarily as a feasibility and design tool for future research rather than a definitive efficacy trial.

• Methodological Contribution: The study successfully demonstrated the feasibility of a 12-week crossover design with a 4-week washout period in a clinical setting. It highlights that the COAST and COASTeR tools showed less variability than owner-reported HCPI and LOAD scores in this specific cohort, though the latter showed larger median changes.
• Effect Size Estimation: The primary contribution is the generation of pilot-derived effect sizes and variability data. These metrics provide realistic parameters for calculating sample sizes in future, adequately powered randomized controlled trials.
• Safety Profile: The study reinforces existing literature suggesting that oral CBD oil is generally well-tolerated in dogs with OA, even when used as an adjunct to other analgesics.
• Limitations and Context: The authors explicitly state that the small sample size (n=10) and the inclusion of dogs with advanced OA (many in the highest pain categories) limit the generalizability of the findings. They note that the use of salmon oil in both the active and placebo arms may have introduced a background anti-inflammatory effect, potentially attenuating measurable differences between treatments. Furthermore, the lack of standardized concurrent analgesic use across the cohort introduces potential confounding variables, though the crossover design helped mitigate this by using each dog as its own control.

In conclusion, the paper claims that while oral CBD oil was safe, it did not produce large or consistent reductions in pain scores compared to placebo in this small pilot cohort. The study's value lies in providing the necessary data to design robust, large-scale trials to definitively evaluate the analgesic potential of CBD in canine osteoarthritis.