Each year, approximately 75,000 Canadians undergo knee replacement surgery, and up to 25% develop persistent post-surgical pain. Persistent post-surgical pain is associated with depression, anxiety, unemployment, and reduced quality of life. Chronic pain after surgery is often managed with opioid therapy, which typically provides only modest benefits and is associated with rare but serious adverse events, such as overdose and death. A number of studies have found that greater pain just before and after knee replacement surgery is associated with the development of chronic pain, suggesting that reducing peri-operative pain may help prevent persistent post-surgical pain.

Medicinal cannabis has begun to emerge as a potential therapy for pain reduction, and produces effects largely due to 2 active components: (1) cannabidiol (CBD), and (2) tetrahydrocannabinol (THC). Studies of CBD have shown analgesic, anti-inflammatory, and anti-anxiety properties, but without the psychoactive effects (feeling 'high') that THC produces. This study will assess the feasibility of a definitive trial to explore whether adding CBD dominant vs. placebo to usual care before and after surgery can reduce the rate of persistent post-surgical pain after total knee replacement. This study will randomize 40 patients to receive either CBD dominant or placebo, and follow them for six months to confirm our ability to recruit patients, adhere to protocol, and capture full outcome data for at least 85% of patients.

Approximately 25% of patients develop persistent post-surgical pain (PPSP) after undergoing total knee arthroplasty (TKA), and higher pre-surgery and acute post-operative pain are associated with this outcome. Medicinal cannabis has anti-inflammatory and analgesic properties and may reduce peri-operative pain and the rate of PPSP following TKA. Cannabidiol (CBD) is the active ingredient of interest because of its anti-inflammatory effects and lack of psychoactive effects seen with tetrahydrocannabinol (THC). The primary objective of this pilot trial is to assess the feasibility of a definitive trial to determine the effect of medicinal cannabis, versus placebo, on the proportion of patients experiencing PPSP following TKA. The primary objective of the definitive trial is to determine if medicinal cannabis add-on therapy, versus placebo, reduces the proportion of patients experiencing PPSP at 6 months following TKA. The secondary objectives of the definitive trial are to determine if medicinal cannabis, versus placebo, reduces opioid use, reduces peri-operative pain interference, improves physical functioning, mental functioning, return to function, anxiety and depression, and sleep. The effect of medicinal cannabis, versus placebo, on the incidence of adverse events at 6 months post-surgery will also be examined. In this blinded multi-centre pilot trial, 40 patients will be randomized to receive either oral capsules of CBD oil or visually identical placebo in addition to standard of care pain medications. Participants will be followed for 6 months.

Inclusion Criteria:

• Patients undergoing TKA aged 18 or older
• Cognitive ability and English-language skills required to complete outcome measures
• Provision of informed consent
• Successful completion of the run-in period

Exclusion Criteria:

• Severe cardio-respiratory disease (For operationalizing: ASA 4/NYHA 4)
• Substance use disorder based on DSM-V criteria
• Allergy or intolerance to cannabis, cannabis derivatives, or other ingredients of the study drug
• Patients who are pregnant, planning to be pregnant, or breastfeeding
• Revision TKA
• Bilateral TKA
• Presenting for their pre-surgical consultation less than 4 weeks before surgery
• Patients with a chronic pain condition affecting the knee (other than osteoarthritis) (e.g.: patients with knee pain due to fibromyalgia or chronic pain syndrome will be excluded)
• Unwilling or unable to follow the study protocol