Knee osteoarthritis is one of the most common joint conditions in the world. It causes pain, stiffness, and trouble moving for millions of people. Many treatments help some people but not others. Because of this, researchers keep looking for new approaches.
A new clinical trial has just been published in the journal Anesthesiology. It tested whether combining a cannabis-based medicine with a strong opioid pain medicine could help people with knee osteoarthritis.
In this article, we look at what the trial did, what it found, and what it might mean for people living with knee pain.
What is knee osteoarthritis?
Osteoarthritis is the most common joint disease in the world. About 7.6% of people were living with it in 2020. It can affect many joints, but it most often affects the hips, hands, and knees.
It happens when the smooth tissue inside a joint, called cartilage, slowly wears down. Without this cushion, the bones do not glide as easily. This may cause:
- Pain when moving
- Stiffness, often worse in the morning
- Swelling around the joint
- A feeling of grating or rubbing
Many things can raise the risk, such as age, past joint injury, body weight, and family history.
How is knee osteoarthritis usually managed?
There is no single treatment that works for everyone. Most people start with simple steps such as:
- Gentle exercise and physiotherapy
- Weight management
- Everyday painkillers
- Hot or cold packs
- Supportive footwear or walking aids
If these do not help enough, a doctor may discuss other options. These could include stronger pain medicines, joint injections, or in some cases surgery. Each option carries its own benefits and risks. The right choice depends on the person and should always be made with a healthcare professional.
What is Dronabinol?
Dronabinol is a synthetic cannabinoid that mimics the structure of delta-9-tetrahydrocannabinol (THC) – the most abundant cannabinoid produced by the cannabis plant. It is a prescription-only medication, which may be considered for the treatment of several conditions when other treatments have been ineffective.
Why are researchers looking at cannabinoids and opioids together?
Strong opioid pain medicines are sometimes used for ongoing pain when other treatments do not help. They can ease pain, but they may also cause side effects such as sickness, sleepiness, and constipation. Some people may also become dependent on them.
For these reasons, scientists are searching for ways to reduce how much opioid medicine people need to take. One idea has come from animal studies. These early studies suggested that adding a cannabinoid to an opioid might let people use a lower opioid dose while still getting good pain relief. This is sometimes called an “opioid-sparing” effect.
So far, studies in people have given mixed results. The recent trial we look at below is one of the few rigorous human studies on this question.
What did the researchers do?
A research team at Johns Hopkins University in the United States ran a small clinical trial. It included 21 adults with knee osteoarthritis. The average age of those taking part was 63.
The study was a double-blind, randomised, placebo-controlled trial. That means:
- Each person took part in four separate sessions
- In each session they took a different combination of capsules
- Neither the patient nor the staff knew which combination it was at the time
The four conditions were:
- Placebo only (no active medicine)
- Dronabinol only
- A strong opioid pain medicine (hydromorphone) only (at a low dose)
- Dronabinol and hydromorphone together
Each session, researchers measured pain in several ways. They also tested thinking skills (such as memory), physical tasks (like walking and stair climbing), and how people felt.
What did the study find?
Pain results
- The combination of the cannabinoid and the opioid did not give better pain relief than either medicine on its own.
- The opioid alone did improve some pain measures more than placebo.
- The cannabinoid alone improved a few measures compared with placebo, but it did not do better than the opioid.
- The combination did not outperform the opioid alone.
There were also no clear differences between the four conditions for everyday clinical pain or for physical tasks such as walking distance, the timed up and go test, or stair climbing.
Side effects
Side effects were tracked carefully:
- About 28% of sessions had a study-related side effect.
- No serious side effects happened in the trial.
- The four conditions did not differ in how often or how strongly side effects appeared.
This was a better safety picture than in an earlier trial by the same team that had used a higher dose of the opioid.
Thinking and memory
The opioid alone made working memory worse compared with all other conditions. The combination slowed reaction time on a memory task compared with placebo. The cannabinoid alone did not appear to harm thinking skills in this trial. The researchers said this finding is interesting but not strong, and more work is needed.
Outcomes included clinical and experimentally induced pain (quantitative sensory testing [QST]), physical and cognitive function, subjective drug ratings, and adverse events. These were evaluated at baseline and at 60, 120, 180, and 240 minutes after dosing.
Important limitations of this study
This was one small, short-term study. Several limits should be kept in mind when reading the results.
Only 21 people took part. This is a small sample size.
The study tested a single dose of each medicine. We do not know what other doses might do.
The cannabinoid was given as a swallowed capsule. This is different from how many cannabis-based medicines are used in real life (for example, inhaled or as oils).
A pure synthetic cannabinoid is also not the same as cannabis flower or cannabis oil, which can contain many other natural compounds.
The trial only looked at short-term effects (one dose at a time), not at what happens over weeks or months.
The first session was always the opioid session, so it was not fully randomised. This may have affected the results.
Because of these limits, the findings cannot be applied to all cannabis-based medicines or to long-term use. They also cannot tell us whether other doses or other forms might work differently.
What might these findings mean?
In short, this trial does not support combining a swallowed synthetic cannabinoid with this opioid for knee osteoarthritis pain. The researchers themselves say more work is needed before drawing wider conclusions.
This is one piece of a much larger puzzle. Different forms of cannabis-based medicines, different doses, and longer-term studies could give different results. Other research, including registry data from people prescribed cannabis-based medicines in the UK, has reported some changes in pain and quality of life. But that kind of study cannot prove that the medicine caused the change. Only well-designed trials can do that.
If you live with ongoing knee pain, the most important step is to speak to a healthcare professional. They can look at your full picture and discuss the options that might suit you.
If you’d like to learn more about medical cannabis and cannabinoids for osteoarthritis, you can complete our eligibility check to see whether a consultation might be suitable for you.
