A new randomized controlled trial from Canadian researchers is offering an intriguing signal that a CBD-dominant cannabis oil taken before and after total knee replacement may reduce the likelihood of developing chronic postsurgical pain. The multicenter pilot study, published August 25, 2026 in the Journal of Cannabis Research, compared a cannabis-derived oral oil containing approximately 25 parts cannabidiol (CBD) to one part tetrahydrocannabinol (THC) with placebo in patients undergoing total knee arthroplasty. At 12 weeks after surgery, moderate-to-severe chronic postsurgical pain was reported by 13% of patients assigned to the cannabinoid treatment compared with 41% of those receiving placebo.
Those numbers are notable, but they require an important qualification. This was a 37-person pilot trial designed primarily to determine whether a much larger randomized study would be practical, not a trial statistically powered to prove that cannabis prevents chronic pain. The researchers themselves describe the pain results as secondary clinical outcomes and conclude that a definitive multicenter trial is still needed. Even so, the substantial difference seen at 12 weeks gives researchers a reason to continue investigating whether cannabinoids used around the time of surgery might influence the transition from acute surgical pain to persistent pain months later.
Researchers Tested Cannabis Before and After Knee Replacement
The study was led by researchers affiliated with McMaster University, the Michael G. DeGroote Centre for Medicinal Cannabis Research, St. Joseph’s Healthcare Hamilton, the University of Toronto and St. Michael’s Hospital. Thirty-seven patients scheduled for total knee arthroplasty were randomly assigned to either MPL-001, an oral cannabis oil, or a matching placebo in addition to standard surgical care. Nineteen participants were randomized to cannabis and 18 to placebo. The average participant was 66 years old, 76% were women, and 81% reported that they had never previously used cannabis.
Treatment did not simply begin after surgery. Participants started the oil four weeks before knee replacement and continued it for at least six weeks afterward, with some patients permitted to continue for as long as 12 weeks after surgery. The oil was gradually titrated to a maximum of 2.5 milliliters daily, providing as much as 125 mg CBD and 5 mg THC per day. Most patients who actually started treatment—28 of 36, or 78%—were able to reach that maximum dose. Researchers then followed the participants for 26 weeks after surgery.
This timing makes the trial particularly interesting. Instead of simply asking whether CBD can relieve pain after it has already become chronic, the investigators were exploring whether cannabinoid treatment beginning before the surgical injury might reduce the development of persistent postsurgical pain in the first place. That is a substantially different question from whether someone should take a CBD gummy when their knee hurts.
Chronic Pain Was Much Less Common at 12 Weeks
The most attention-grabbing finding emerged three months after surgery. Among participants with available 12-week data, 7 of 17 people receiving placebo—41%—reported moderate-to-severe chronic postsurgical pain. Only 2 of 15 patients receiving the CBD-dominant cannabis oil—13%—reported pain at that level. That represents an absolute difference of approximately 28 percentage points between the groups.
The apparent advantage was considerably smaller by six months. At the 26-week follow-up, moderate-to-severe pain was reported by 3 of 16 placebo patients, or 19%, compared with 2 of 14 cannabis-oil patients, or 14%. Researchers also pointed out that one of the two treatment-group patients reporting chronic pain at both follow-up points had not actually taken any study medication. Thirty of the original 37 participants completed the 26-week assessment.
The shrinking difference is one of the reasons the results should not be interpreted as proof that CBD-dominant cannabis prevents chronic pain after knee replacement. The early signal was substantial, but the groups were tiny. Changing the outcome of just two or three patients would dramatically alter the percentages. A larger randomized trial is needed to determine whether the 12-week difference represents a reproducible treatment effect or the statistical instability that can occur in very small studies.
Chronic Pain After Knee Replacement Is a Major Unsolved Problem
Total knee replacement is one of the most effective surgical treatments for severe knee osteoarthritis, but replacing the joint does not guarantee that pain disappears. Earlier systematic research estimated that approximately 20% of knee-replacement patients continue to experience chronic pain, while more recent analyses have suggested persistent pain may affect roughly one in four patients depending on the definition and population studied.
A 2024 systematic review involving 32 studies and 18,792 patients identified several factors strongly associated with chronic postoperative pain after total knee arthroplasty, including greater preoperative pain, chronic widespread pain, sleep disorders, anxiety, poorer preoperative function and central sensitization. Another systematic review found particularly strong evidence linking persistent pain with severe acute postoperative pain and pain catastrophizing. These findings have encouraged researchers to investigate interventions that might interrupt the biological and psychological processes through which intense surgical pain becomes chronic.
That is the larger context for the McMaster-led cannabis trial. The objective was not simply to make the first few days after surgery more comfortable. Researchers were interested in whether cannabinoid treatment across the perioperative period could influence the development of chronic postsurgical pain, a condition that can persist long after the surgical wound itself has healed.
This Was CBD-Dominant Cannabis Oil—Not Pure CBD
Although CBD was the dominant cannabinoid, describing MPL-001 simply as “CBD” misses an important detail. The oil contained approximately 50 mg/mL CBD and 2 mg/mL THC, producing its 25:1 CBD-to-THC ratio. It also contained smaller quantities of other naturally occurring cannabinoids, including cannabichromene (CBC), cannabinol (CBN) and cannabigerol (CBG).
At the maximum daily dose, participants therefore received about 125 mg CBD plus 5 mg THC rather than isolated cannabidiol. Five milligrams of THC is relatively modest compared with many recreational cannabis products, but it is pharmacologically meaningful. Because the trial tested this specific multi-cannabinoid formulation, the results cannot automatically be transferred to store-bought CBD isolate, hemp gummies, smoked marijuana or high-THC cannabis.
That distinction matters because broader pain research has not consistently found that CBD alone is a strong analgesic. The U.S. Agency for Healthcare Research and Quality’s continuing review of cannabinoid treatments for chronic pain has generally found little evidence that purified oral CBD alone reduces pain, while certain THC-containing or approximately balanced THC/CBD formulations have shown small improvements in predominantly neuropathic chronic pain. Evidence for many whole-plant and CBD-dominant products remains insufficient.
Previous Knee-Surgery Cannabis Trials Have Been Mixed
The new findings stand out partly because earlier controlled studies of cannabinoids after knee replacement have been much less encouraging. In 2022, investigators at the Rothman Orthopaedic Institute and Thomas Jefferson University randomized 80 knee-replacement patients to topical CBD, CBD plus essential oil, essential oil alone or placebo. Topical CBD did not reduce postoperative pain, opioid consumption or sleep problems during the six-week study.
Another randomized trial published in 2026 tested the synthetic THC medication dronabinol in 163 cannabis-naive patients undergoing total knee replacement. Participants received 2.5 mg twice daily alongside the normal multimodal postoperative pain regimen. Researchers found no reduction in opioid consumption, pain scores, sleep problems or nausea compared with placebo through the early postoperative period.
These apparently conflicting results do not necessarily cancel each other out because the studies tested very different interventions and outcomes. Topical CBD was used after surgery for acute pain. Dronabinol delivered isolated THC and focused largely on opioid consumption during the first several weeks. The new McMaster trial used a CBD-dominant full-spectrum oil beginning a month before surgery and focused on whether patients developed persistent pain months later. Different cannabinoids, doses, routes and treatment windows could produce very different results.
Safety Looked Generally Similar to Placebo
The researchers did not identify an obvious major safety signal in the small pilot trial. There were 18 treatment-related adverse events among 11 participants assigned to MPL-001 and 19 treatment-related events among 12 placebo recipients. Gastrointestinal complaints—especially nausea and diarrhea—were the most common problems in both groups.
That does not establish long-term safety. With fewer than 40 participants, the trial was far too small to detect uncommon adverse effects reliably. High-dose CBD can interact with prescription drugs through liver-enzyme pathways, while THC can produce dizziness, sedation, altered coordination and cognitive effects. Patients undergoing joint replacement are frequently older and may simultaneously receive opioids, anticoagulants, anti-inflammatory drugs and other medications, making drug interactions and additive side effects relevant considerations.
Still, the fact that most participants were cannabis-naive and that 78% of those starting medication reached the maximum study dose provides useful preliminary tolerability information. The treatment was not obviously intolerable simply because participants were unfamiliar with cannabis.
Adherence Was One of the Trial’s Biggest Problems
Ironically, one of the clearest lessons from the study may have been about the oil-drop formulation rather than pain relief. The investigators originally established adherence as one of their primary feasibility objectives. Seventy-one percent of participants took at least 75% of their assigned medication before surgery, but only 48% reached that adherence threshold after surgery.
That is a significant problem for a future efficacy trial because researchers cannot accurately determine whether a treatment works if large numbers of participants do not consistently take it. The investigators therefore plan to alter their protocol by expanding recruitment to more centers and replacing oil drops with capsules, which they believe may improve treatment adherence.
The pilot was originally designed specifically to identify problems like these before launching a much larger and more expensive study. In that respect, the less-than-ideal adherence does not make the research unsuccessful; it provides information needed to design a stronger definitive trial.
The Results Challenge a Simple Story About CBD and Pain
The new trial arrives at an interesting moment in cannabinoid pain research. Systematic reviews have increasingly concluded that cannabis-related medicines can offer small pain improvements for some patients, but the evidence depends heavily on the cannabinoid formulation. AHRQ’s review found that approximately balanced THC/CBD products produced small average improvements in chronic pain, while CBD-dominant and isolated CBD products generally have not demonstrated consistent analgesic benefits. Dizziness, sedation and nausea also increase with several THC-containing treatments.
A 2021 international BMJ clinical guideline consequently issued only a weak recommendation for a trial of non-inhaled medical cannabis or cannabinoids in people with chronic pain when standard treatments are insufficient. The recommendation was deliberately cautious because the expected improvements in pain, sleep and function are generally small and must be balanced against side effects and uncertainty about long-term outcomes.
The knee-replacement trial may be investigating something subtly different. Rather than treating established chronic pain, it raises the possibility that cannabinoid therapy during the period surrounding surgery could alter the probability that chronic pain develops. If that effect were eventually confirmed, it would represent a potentially different clinical role for cannabinoids.
What a Larger Trial Needs to Prove
The obvious next question is whether a sufficiently large randomized trial can reproduce the 41% versus 13% difference at 12 weeks. A definitive study would need enough patients to provide narrow confidence intervals, maintain strong treatment adherence and determine whether any reduction in chronic pain persists at six months or longer. It would also need to clarify whether treatment improves physical function, sleep, quality of life and return to everyday activities rather than merely changing a pain classification.
Researchers will also need to determine whether there is a meaningful opioid-sparing effect. The pilot included opioid use among its secondary outcomes, but current evidence concerning cannabinoids and postoperative opioid requirements remains inconsistent. The negative 2026 dronabinol trial reinforces the need to test opioid reduction rather than assume that it occurs.
Finally, future research may need to determine which component of MPL-001 matters. Is the signal largely related to CBD? Is the small quantity of THC necessary? Do CBC, CBG or CBN contribute? Or does beginning treatment four weeks before surgery matter more than the precise cannabinoid ratio? The present study cannot answer those mechanistic questions.
The Bottom Line
The newly published randomized pilot trial provides one of the more interesting recent signals in cannabinoid-based surgical pain research. Three months after knee replacement, moderate-to-severe chronic postsurgical pain occurred in 13% of patients assigned to a 25:1 CBD-dominant cannabis oil compared with 41% receiving placebo. The oil was started four weeks before surgery and continued for at least six weeks afterward, with a maximum daily exposure of approximately 125 mg CBD and 5 mg THC.
But this is precisely the kind of result that needs confirmation rather than immediate clinical adoption. Only 37 patients were randomized, pain outcomes were secondary to the study’s feasibility objectives, medication adherence was relatively poor after surgery, and by 26 weeks the difference between groups had narrowed to 14% versus 19%. The trial therefore does not establish CBD-dominant cannabis oil as a proven treatment for knee-replacement patients.
What it does provide is a scientifically credible reason to run the larger study. If future trials confirm that perioperative CBD-dominant cannabis therapy can meaningfully reduce the transition from acute surgical pain to chronic pain—without creating unacceptable side effects—it could open a new direction for postoperative cannabinoid research. For now, the most accurate conclusion is also the most interesting one: the signal is promising, but the definitive test has yet to be done.
