Cannabis in Parkinson's disease

Dr Sona A Pungavkar *

With medicinal Cannabis now being legalized in most parts of the western world, there is much discussion about it's use in many illnesses, including in patients suffering from Parkinson's disease. Parkinson's and related diseases can have genetic and environmental causes.

In Parkinson's disease, the areas in the brain producing and using the neurotransmitter, called as dopamine, get affected by degenerative process. These include substantianigra and corpus striatum. Dopamine is produced in the substantianigra and transmitted to the striatum via dopamine pathways.

The striatum is responsible for the movements. When there is loss of the neurons producing the dopamine, due to various causes, the striatum does not receive the dopamine in the required amounts and hence, there is inability to perform the movements. Hence, the patient experiences abnormal excessive movement called as tremors, rigidity, imbalance, and lack of spontaneous movement.

Lewy bodies are abnormal protein aggregates within neurons in the substantianigra. The primary abnormality in these structures is alpha-synuclein. These are in neurons of all patients with Parkinson's disease. Lewy bodies can be found in other brain areas such as the amygdala, degeneration of which caused anxiety and depression. Lewy bodies in the cortex and hippocampii lead to dementia.

Patients also suffer from insomnia, nausea, loss of appetite and pain. As the disease progresses, other areas in the brain are also affected, adding to the severity of the symptoms.

The medical treatment is directed to increase the production of dopamine in the brain and control of other symptoms. Medical treatment at present includes dopamine promoters and agonists, in addition to supportive treatment in terms of physiotherapy, counselling and nutrition.

The endocannabinoid system is located in the brain and made up of cannabinoid receptors. Medicinal Cannabis contains manyneuroactive chemicals that work with two types of cannabinoid receptors, type 1 (CB1) located in the brain and type 2 (CB2) located in the brain and peripheral immune system.

Cannabinoids have powerful, indirect effects on these receptors, but more research is required to understand the same. People with Parkinson's have less CB1 receptors than people who do not have Parkinson's disease. CB1 receptor are stimulated bythe cannabinoids and thus can improve tremors and help in dyskinesia. Similarly, the other receptor, CB2, could also modify the disease and provide neuroprotective benefits, though the mechanism is not certain.

The cannabinoids found in medicinal Cannabis are probably of two types – an agonist, one which works same as the natural molecule, causing similar effect and an antagonist, one which attaches to the receptor but blocks the effect. The concentrations of each of these, varies in different strains of the plant and would be affected by the extraction processes. Hence, it is difficult to study the effects of medicinal Cannabis and document the same.

Medicinal Cannabis can be administered asa capsule, nasal spray or liquid formulation. The nasal spray would have prompt action due to quick absorption. The effect with the capsules can be expected after a few hours, as the absorption from the gut would take longer.

Several studies in support of use of medicinal Cannabis have been published so far. One of these by Myers et al in a reputed, peer-reviewed journal, Neurology, in August 2019, has taken into account results in more than 50 patients of Parkinson's disease who were treated with medicinal Cannabis in addition to the ongoing allopathic therapy.

It reports that in combination with other PD therapies, medicinal Cannabis is well-toleratedand helps to improve motor as well as non-motor symptoms. In addition, it could also help in alleviating some of the side effects of the medications such as nausea or insomnia.

77 % patients had improvement in tremors and spasticity. Some of the patients who were also on opioid medication could stop the medication.Benefits were also seen in the non-motor symptoms, including insomnia, anxiety, depression, and nausea. 44 % patients had side effects such as excessive sleepiness and giddinessdue to medicinal Cannabis, which could be countered in 41 % patients with dose. A very small percentage of patients (6 %) had to discontinue the medicinal Cannabis, as they could not tolerate it.

The Parkinson's Foundation has a study in which it has documented the perspectives of the physicians involved in the management of Parkinson's disease, regarding the use of Cannabis. One surprising point of this study is that 80 % of the patients had already used Cannabis, and 95 % of the neurologists had a request from the patients to be prescribed Cannabis, although the patient population was assessed over 40 centres, spread over a wide geography.

As most physicians have heard or read of medicinal Cannabis and it's effects, but they did not have detailed information, 93 % wanted Cannabis to be taught in medical school

Most specialists dealing in Movement Disorders do not recommend replacing the dopaminergic and other approved therapies with medicinal Cannabis.

However, as an adjunct, medicinal Cannabis is a good option and can be used judiciously. The best way to administer medicinal Cannabis needs to be researched. Also, the doctors and support staff as well as the family members need to trained regarding the use of medicinal Cannabis.