Contaminants pose risk as use of cannabis for Parkinson’s rises: Study

Doctors lack information on common contaminants, survey finds

Margarida Maia, PhD avatar

by Margarida Maia, PhD |

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Various forms of cannabis-based treatments, from oils to to capsules and leaves, are shown.

The use of medical cannabis in the U.S. has grown as more states legalize it, and programs listing Parkinson’s disease-related conditions, including muscle cramps, anxiety, and pain, have expanded from 28 states to 36 in just five years. Yet a survey found many doctors are not aware of the prevalence of contaminants such as pesticides or solvents, which increase the risk for Parkinson’s.

That suggests a need for better regulations and education, researchers wrote in the study, “Cannabis Use in Parkinson’s Disease: Patient Access to Medical Cannabis and Physician Perspective on Product Safety” published in NeuroToxicology.

The dried leaves and flowers of the cannabis plant contain cannabinoids, a type of compound used in the clinic to alleviate symptoms associated with many diseases, including Parkinson’s.

People with Parkinson’s find that cannabis helps them with both motor and nonmotor symptoms, and its use is about twice as common as in the general population. Like any other medications, however, cannabis also comes with risks, including contamination.

It’s thought that people with Parkinson’s may be particularly vulnerable to contaminants like environmental toxins and pesticides. However, it’s unclear whether patients and their doctors are aware of contamination risks.

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Uneven descriptions, criteria across states

A team of researchers in the U.S. watched for changes in the number of states that list Parkinson’s or any related conditions as eligible to receive treatment with medical cannabis from 2019 to 2023. 

They found that over these five years, the number of states listing one or more conditions related to Parkinson’s increased from 28 to 36. Conditions qualifying for cannabis use included Parkinson’s itself, which went from listing in 14 states in 2019 to 16 states in 2023, muscle cramps (14 to 24), anxiety (1 to 5), and pain (17 to 35).

The language used to describe qualifying conditions isn’t uniform, the researchers found. For example, muscle cramps and anxiety may not be explicitly listed but can qualify under broader conditions. Pain is often described with a wide range of specific terms, the researchers said.

An online survey was sent to 45 neurologists and movement disorder specialists, but only 20, from nine states, returned it. Twelve doctors said fewer than 20% of their patients used cannabis, while the other eight put the figure at 20% to 40%.

While most doctors (80%) knew which types of programs were active in their states, less than half (40%) were able to correctly identify which specific conditions were eligible to receive treatment with cannabis.

Two-thirds (65%) were unable to identify common contaminants from a list, “although all of the contaminants provided in the list were often found in cannabis,” the researchers wrote. Few knew about the presence of pesticides (25%), toxic elements (15%), or solvents (15%).

“Despite the potential exposure risk to pesticide, toxic element, and solvent contaminants in cannabis, our online survey revealed a lack of awareness by neurologists and movement disorder specialists regarding cannabis contamination,” the team wrote.

At the end of the survey, the doctors were given a summary of common contaminants found in cannabis products and then asked two open-ended questions to get their newly informed perspectives on the risks.

The top concerns were the impact of contaminants on comorbidities (coexisting health conditions) and Parkinson’s prognosis (40%) and long-term effects (35%). When asked about policy changes to cut contaminants, the most common suggestions were stricter regulations, medical and public education, and more research.

“Although the current cannabis policies in the U.S. are ahead of the science, education and research can fill the gap by informing health providers about past experiences with patients and current challenges or conundrums,” the team wrote.