Cannabis, also known as marijuana, comes from the Cannabis sativa plant which is thought to contain around 100 different compounds known as cannabinoids. Its main cannabinoid is tetrahydrocannabinol (THC) which is known to be a psychoactive drug, that is a substance that affects brain function. THC may help with pain, nausea and muscle spasms but it also alters mental processes, behaviour, mood, consciousness and perception.

The second most common cannabinoid is cannabidiol (CBD) which does not have psychoactive properties but many believe it may be beneficial in treating a wide range of conditions such as multiple sclerosis, chronic pain, depression and Parkinson’s. In 2018 a major study¹ found cannabis to be beneficial in treating some cancer-related symptoms (pain, sleep problems and nausea) but evidence for its benefits for other symptoms and conditions remains elusive.

Cannabis can be taken in different forms and ways, for example, smoking dried leaves, as a spray under the tongue or as tablets. THC and CBD are thought to be largely responsible for the effects of cannabis although their mechanisms of action are not fully understood.

The concentrations of THC, CBD and other cannabinoids vary from one form to another, and also from one plant to another. This variability is one of a number of challenges encountered in clinically evaluating the effects of cannabis, both alone and in combination with other medications.

References:

1. Prospective analysis of safety and efficacy of medical cannabis in large unselected population of patients with cancer. European Journal of Internal Medicine 2018 Mar. Vol. 49; 37-43 - view article

Our bodies naturally make cannabinoids that control various processes, such as mood, sleep and appetite, by binding to cannabinoid receptors throughout the brain and body. We have two main types of cannabinoid receptor, which are like switches outside cells that trigger a biological reaction within a cell once the receptor is activated: CB1 receptors are located in the brain and respond to THC which results in the ‘highs’ associated with cannabis use; CB2 receptors are found mainly on cells relating to the immune system and on brain cells believed to be responsible for pain relief.

There are concentrations of cannabinoid receptors in the basal ganglia area of the brain, where dopamine-producing neurons are located and which is known to be involved in the movement symptoms of Parkinson’s. Researchers have therefore speculated that a substance such as cannabis, which binds with cannabinoid receptors in an area of the brain so closely involved in Parkinson’s, may positively affect the symptoms of the condition. Extensive research into this is underway.

Although cannabis has been used since ancient times for relieving pain, improving sleep and for many other purposes, there is still very little evidence regarding its efficacy and safety.

Studies have suggested that cannabis may have antioxidant, anti-inflammatory and neuroprotective properties but much more research is needed to understand this. Neuroprotection is of particular interest in Parkinson’s due to the loss of dopamine-producing neurons.

Anecdotal evidence and some clinical studies have suggested that cannabis may help with symptoms in a wide range of conditions, including Parkinson’s. But despite some promising suggestions, using animal models, that cannabis may help with movement symptoms such as tremor, slowness and levodopa-induced dyskinesia, there have been mixed and often confusing results. In non-motor symptoms such as pain, sleep problems, anxiety, depression, memory problems and hallucinations, research is also ongoing with some encouraging results but side-effects are common and we need to understand more before any conclusions are drawn.

Unfortunately, many clinical studies into cannabis as a Parkinson’s treatment have been hampered by regulatory restrictions or have had various shortcomings. For example, some have not been conducted using the gold standard double-blind, placebo-controlled trial design, many include only a small number of participants, and variable concentrations of CBD and THC (depending on how cannabis is consumed) make it difficult to compare outcomes. As a result, many study results are not widely acknowledged because minimum research standards have not been met.

There is, therefore, a renewed focus on conducting more rigorous studies in large cohorts of patients before any conclusions regarding the potential benefits in treating Parkinson’s symptoms can be reached. These studies will need to establish which symptoms can be alleviated, in whom, appropriate dosages and how cannabis can be safely administered, particularly in the long-term, so as to eliminate associated risks such as addiction and increased risk of heart or lung problems, and side-effects such as nausea, dizziness, hallucinations, physical weakness and cognitive changes.

Until unambiguous trial results are available, cannabis should be used with great caution in Parkinson’s because of its associated risks, including addiction. Cannabis affects thinking and executive function, which are already frequently impaired in those with the condition. It should not be taken as a substitute for dopaminergic and other approved Parkinson’s treatments. You should always seek medical advice before taking cannabis in any form.

In many countries, taking cannabis is illegal and may result in imprisonment if you are caught with the drug. It can also impair judgement which presents a real danger when driving or carrying out other hazardous activities.

Cannabis may be a future Parkinson’s treatment but for now, we need conclusive evidence of the benefits and to better understand appropriate formulations and dosages, the side-effects and interactions with other medications, and any long-term risks. A lot more research is required both in the lab and in clinical trials, including into specific molecules isolated from the plant, in order to achieve these goals.

Content last reviewed: August 2018

We would like to thank Prof Peter Jenner (King's College, London, UK) for his help in reviewing this information.

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Guidelines

• Royal College of General Practitioners – Cannabis-based medication: an interim desktop guide

Selected research papers:

• Martins de Faria s, de Morais Fabrício D, Tumas V, Costa Castro P, Antonelli Ponti M, Hallak J, Zuardi A, Crippa J, Hortes Nisihara Chagas M. Effects of acute cannabidiol administration on anxiety and tremors induced by a Simulated Public Speaking Test in patients with Parkinson’s disease. Journal of Psychopharmacology 2020 Jan 07 [Epub ahead of print] – read more
• Abrams DI. The therapeutic effects of Cannabis and cannabinoids: An update from the National Academies of Sciences, Engineering and Medicine. European Journal of Internal Medicine, 2018 March. doi: 10.1016/j.ejim.2018.01.003
• Chagas MH, Eckeli AL, Zuardi AW, Pena-Pereira MA, Sobreira-Neto MA, Sobreira ET, Camilo MR, Bergamaschi MM, Schenck CH, Hallak JE, Tumas V, Crippa JA. Cannabidiol can improve complex sleep-related behaviours associated with rapid eye movement sleep behaviour disorder in Parkinson's disease patients: a case series.  J Clin Pharm Ther. 2014 Oct 21. doi: 10.1111/jcpt.12179
• Koppel BS, Brust JC, Fife T, Bronstein J, Youssof S, Gronseth G, Gloss D. Systematic review: efficacy and safety of medical marijuana in selected neurologic disorders: report of the Guideline Development Subcommittee of the American Academy of Neurology. Neurology 2014 Apr 29;82(17):1556-63. doi: 10.1212/WNL.0000000000000363
• Lotan I, Treves TA, Roditi Y, Djaldetti R. Cannabis (medical marijuana) treatment for motor and non-motor symptoms of Parkinson disease: an open-label observational study. Clin Neuropharmacol. 2014 Mar-Apr;37(2):41-4. doi: 10.1097/WNF.0000000000000016
• Gowran A, Noonan J, Campbell VA. The multiplicity of action of cannabinoids: implications for treating neurodegeneration. CNS Neurosci Ther. 2011 Dec;17(6):637-44. doi: 10.1111/j.1755-5949.2010.00195.x.
• Volkow ND, Baler RD, Compton WM, Weiss SR. Adverse health effects of marijuana use. N Engl J Med. 2014 Jun 5;370(23):2219-27. doi: 10.1056/NEJMra1402309

Articles

• Dr. Michelle Sexton – Expert Voices: Can Cannabis Use Help With Parkinson’s Symptoms?