Using Medical Cannabis to Reduce Harms associated with Long-Term Opioid Use in Chronic Pain

Trends in Registration and Reasons for Use of Medical Cannabis in the US

In recent years, cannabis has become increasingly accessible to citizens in many countries around the world, notably in the US. The majority of this access is restricted to medical uses; however, the US recreational cannabis market is also continuing to grow. As of July 2022, 37 states had legalised medical cannabis and 18 also permit recreational use. While over half of US citizens now live in a state where both medical and recreational cannabis is legal, these policies continue to conflict with the federal law on cannabis – namely the Controlled Substances Act in which cannabis is still defined as having no accepted medical uses. 

This conflict is the source of significant uncertainty, particularly relating to qualifying conditions, knowledge among healthcare providers and dispensary employees, and manufacturing and testing requirements of medical cannabis products. Furthermore, evidence suggests that in markets where recreational cannabis is also legal, many patients use recreational products for medical purposes.

Understanding the reasons for medical cannabis use and whether this is affected by recreational legalisation is, therefore, an important consideration when attempting to develop effective public and medical policy around cannabis. With this in mind, the authors of a recent study (June 2022) aimed to identify trends in registration for medical cannabis and the most common reasons for use.

Design and Methods

In order to identify these trends, the researchers analysed data from medical cannabis registries across the US using publicly available reports and data requests from government departments overseeing medical cannabis programs. Data collected between 2016 and 2020 were included for analysis. Raw patient numbers were identified and an enrolment rate per 10,000 population was calculated for each state using year-specific estimates for state population from the US Census. The researchers also investigated trends in patient-reported qualifying conditions. Data from recreational and medical-only states were also compared.

The Results

In 2020, Washington D.C. and 26 of the 35 states with a legal medical cannabis market reported their patient numbers. Only 19 of these states reported the number of patient-reported qualifying conditions. However, some states only reported data in certain years, did not report complete data or did not consistently publish reports. 

Patient Enrolment

The researchers identified a significant acceleration in patient enrolment from 678,408 in 2016 to 2,974,433 in 2020 – an approximately 4.5-fold increase. The patients per 100,000 total population also increased during this period. This increase was driven by improved availability of medical cannabis due to the implementation of new laws (35 states and Washington, DC had enacted laws by 2020 vs. 23 and Washington, DC in 2016). Interestingly, states that had implemented medical cannabis laws after 2016 accounted for 52.9% of patients in 2020. Increased patient numbers were also linked to growing enrolment in existing programs, “including the expanding licensure for new qualifying conditions”. 

While there was an overall increase in patient enrolment numbers across the whole of the US, population-level enrolment varied considerably between states. For example, enrolment in Alaska was reported at just 0.05%, compared with 9.3% in Oklahoma. The researchers suggest that enrolment patterns such as this may be “influenced by time since legislation implementation, demographics, permissiveness of state laws, and recreational cannabis laws”. 

The latter possibility was demonstrated by decreasing enrolment in five of the seven recreational states monitored. In these states, which permitted both the medical and recreational use of cannabis, it is theorised that patients may have replaced medical cannabis products with recreational ones. This may be due to patients “opting out because they no longer need a license to provide legal cover for recreational use”, to avoid inconvenience and/or licensing fees, or because they are using recreational products medicinally. 

Public Opinion Toward Cannabis

Increased utilisation of medical cannabis programs is likely also influenced by a growing acceptance of cannabis across the US. For example, a 2021 national Pew poll reported that more than 90% of Americans agree that cannabis should be legal for medical purposes – a figure which has been rising in recent years. This acceptance of medical cannabis was further perpetuated throughout Coronavirus social restrictions, in which most medical cannabis markets were designated as “essential”.

Patient-Reported Qualifying Conditions

The analysis of medical cannabis registries which recorded patient-reported qualifying conditions showed that chronic pain was the most common reason for medical cannabis licensure. Chronic pain increased from 484,386 in 2016 to 1,119,668 in 2020, accounting for 60.6% of all patient-reported qualifying conditions in 2020. This is unsurprising given the high prevalence of chronic pain and the fact that it is often a comorbidity with other qualifying conditions. Furthermore, treatment regimens for chronic pain remain largely ineffective, leading many patients to seek alternative therapies – including medical cannabis treatment.

The next most reported condition in 2020 was post-traumatic stress disorder (PTSD) (10.6%) which increased from 27,447 in 2016 to 195,984 in 2020. Other patient-reported conditions included multiple sclerosis, arthritis, and chemotherapy-induced nausea and vomiting.

The researchers note that “the percentage of conditions for which cannabis has substantial or conclusive evidence of therapeutic value decreased from 84.6% in 2016 to 68.2% in 2020”. It is suggested that this is due to increased licensure for PTSD (for which there is limited evidence of medical cannabis efficacy), as well as poor data quality, such as the inclusion of vague categories like “other” or “psychiatric conditions” – for which there can be no evidence of efficacy.


The data analysed in this study show that medical cannabis licensure has increased dramatically since 2016. However, recreational legalisation is identified as a contributor to decreasing licensure. The researchers note that one limitation of this study is the lack of data explaining this trend (why patients no longer obtain licenses after recreational laws are implemented). Other limitations include inconsistent and missing data, lack of details of products used and patient demographics by qualifying conditions, and vague categorisation of qualifying conditions. 

As such, it is recommended that these findings be interpreted with caution. The researchers note that a more coherent cannabis policy across the US would “enhance research efforts to guide appropriate medical cannabis use”. Nonetheless, the available data demonstrates how changing attitudes to medical cannabis, alongside increasing access to legal medical programs has contributed to a significant rise in the number of patients seeking medical cannabis treatment.