Cannabis and Parkinson’s: what do we know?

What is cannabis?

Cannabis is an illegal drug made from the Cannabis sativa plant. It contains over 100 different molecules called ‘cannabinoids’. The two main chemicals are:

• Tetrahydrocannabinol (THC) - the major psychoactive component that affects how the brain works and causes changes in mood, awareness, thoughts, feelings, or behaviour (the chemical that gets you high). It can increase the risk of psychotic illness - where it is hard to distinguish fantasy from reality.
• Cannabidiol (CBD) is another major component that can similarly alter how the brain works but does not cause the “high” associated with THC and may have potential benefits for a range of conditions. CBD-based medicines are already approved for treating severe forms of epilepsy.

Cannabis bought illegally off the street, where the quality, ingredients and strength are not known, is the most dangerous form to use as it often contains high levels of THC.

CBD products are legal to buy in the UK as supplements and contain very low levels of THC. However, if you are considering using CBD products we recommend speaking to a health professional.

Research into cannabis-based treatments for Parkinson’s

There is interest in cannabis-based treatments for people with Parkinson’s because of the way they alter how the brain works.

Experiments in the lab with cannabinoids - using animal models or cells grown in a dish - have shown potential for influencing both motor and non-motor symptoms of Parkinson’s

As well as the hope they hold for improving symptoms, there is also research underway to explore whether cannabinoids could target some of the underlying processes that damage brain cells in Parkinson’s.

But so far, there have been very few clinical trials to test cannabis-based treatments in people with the condition, and those that have been done have been too small to draw any firm conclusions.

This means we do not yet have enough evidence to know whether cannabis-based treatments are safe and what the benefits may be for people with the condition.

New, high-quality clinical trials are now being conducted to investigate the potential of cannabis-based treatments in people with Parkinson’s. Let’s take a look at some of the major studies.

Nabilone for non-motor symptoms

Nabilone is a medicine, taken as a capsule, that has been developed to act in a similar way to THC. It is already used to treat nausea and vomiting in people undergoing chemotherapy treatment for cancer.

A clinical trial carried out in Austria examined the safety and effectiveness of nabilone in 47 people with Parkinson’s with troublesome non-motor symptoms.

All participants received nabilone at the beginning of the study and the amount of the drug was gradually increased. Then participants were randomly chosen to either continue on nabilone or switch onto placebo (inactive treatment).

Results published in 2020 show that nabilone improved non-motor symptoms in the first part of the trial. In the second part, non-motor symptoms worsened for people who switched onto placebo compared to those who remained on nabilone.

Nabilone seemed to particularly improve anxiety and sleeping problems. And the treatment was generally well tolerated with fatigue the most commonly reported side effect.

Longer term follow up of people who took part in this study, published in 2024, continues to support the trial results and show it is safe for longer term use.

Read more about the trial results and follow up in the Nature Partner Journal of Parkinson’s Disease.

Cannabidiol (CBD) for motor symptoms

CBD has been tested in a recent trial carried out in the US to investigate its effects on motor symptoms - things like slowness, stiffness and tremor.

The trial involved 61 people with Parkinson’s. Half received CBD and half received an identical but inactive placebo for 2-3 weeks.  

Results from this short-term study show that people who received CBD experienced slightly improved motor symptoms compared to those who received the placebo. However, the difference between the 2 groups was not large enough to be convincing.

We’re still waiting for the results to be shared and discussed in more detail in a scientific journal.

Read the initial raw results on the clinical trials.gov website.

Cannabidiol (CBD) for Parkinson’s associated psychosis - trial underway now

CBD is also being tested in a major UK trial to investigate its potential for treating psychosis - hallucinations and delusions eg. seeing, hearing or feeling something that isn’t real - in people with Parkinson’s. This trial is called CAN-PDP.

The only treatments currently available to people who experience these distressing symptoms are antipsychotics, which can worsen movement symptoms and can also have possible serious side effects.

Previous studies in people without Parkinson’s have shown that CBD may reduce abnormal brain activity that causes hallucinations and delusions.

The £1.2m study is fully funded by Parkinson’s UK and led by a team at King’s College London.

The trial has identified what dose of CBD should be used in the trial going forward and is now recruiting over 100 people with Parkinson’s to thoroughly assess the safety and potential effects of CBD.

If you or a loved one has Parkinson’s and experience hallucinations or delusions, this study is looking for people to take part.

Find out more about the CAN-PDP study and how to take part.

When will cannabis-based medicines be available for Parkinson’s?

There is currently a lack of good quality evidence for the safety and benefits of cannabis-based treatments for Parkinson’s. 

Until we have robust evidence, cannabis-based medicines cannot be approved and prescribed for Parkinson’s.

But new, high quality clinical trials are starting to happen which is a huge step forward. And we hope to see further trials starting over the next year or two.

We’ll be monitoring the progress of current and new trials and will share news as it happens.

Further reading

Dr Susan Fox, an Associate Professor of Neurology at the University of Toronto, published an article in 2024 in the Journal of Parkinson’s Disease called Advice to People with Parkinson’s in My Clinic: Cannabis which you may find helpful and interesting.