The United States has a complex relationship with cannabis and its legal status, notably a high level of tension between state and federal level (Young-Wolff et al., 2022). At the federal level, cannabis remains classified as a controlled substance under the Controlled Substances Act (1906). This means it is officially regarded as having a high potential for abuse and isn’t a recognised medical treatment option for any disease or condition by the United States Food and Drug Administration.
Despite the federal classification, there has been a movement toward decriminalisation at the state level with many states introducing medical cannabis laws (MCL) and recreational cannabis laws (RCL) (Martins et al., 2016). For MCL across most states, they require patients to have a recommendation from a physician and may have to register with the state’s program. Whereas the majority of RCL require the individual to be aged over 21 and have ID, and they can then purchase cannabis from a wide number of licensed dispensaries.
Military veterans face unique stressors not faced by their civilian counterparts, such as trauma, frequent relocations of themselves and/or family, long-term deployments, and increased prevalence of mental health and physical health disorders (Inoue et al., 2023). One area of growing concern is chronic pain. Research has shown that a portion of veterans report experiencing pain, with many describing it as severe (Nahin, 2016). The reasons vary but can include combat-related injuries, training injuries, and wear and tear from arduous military service.
Chronic pain can impact daily functioning, quality of life, and can be associated with depression, substance use, and sleep disorders. Some veterans have turned to cannabis to help moderate and mediate pain symptoms and improve quality of life.
Therefore, Hasin and colleagues (2023) aimed to see if making cannabis legal for medical or recreational use had any impact on the rise of cannabis-related problems and long-term pain among US veterans using Veterans Health Administration (VHA) services.
The authors looked at the health records of patients who visited primary care, emergency, or mental health services operated by US Veterans Health Administration (VHA) between 2005 and 2019. They excluded patients who were on end-of-life care or currently under an admission. The sample was then split into two groups: those with long-term pain and those without, using the American Pain Society taxonomy of painful medical conditions.
For each group, patients with clinically diagnosed cannabis use disorder were identified based on ICD-9-CM or ICD-10-CM clinical codes. The ‘CM’ references clinical modification which is an altered version of International Classifications of Diseases for use in the United States only. Importantly, patients were excluded if they were in remission or had an unspecified cannabis use disorder code.
The sample was analysed using linear binominal regression models which were stratified by pain and a time-varying state-level law status. This time-varying state was based on the legalisation of cannabis for medical use in each state. In addition, patient covariates such as age, sex, race, and ethnicity were also used to adjust the models.
In total, 15 cross-sectional yearly datasets representing each year between 2005 and 2019 were analysed. This represented between 3,234,383 and 4,579,994 patients depending on the year. The key findings of the study were:
- In 2005, among patients without chronic pain, 5.1% were female with an average age of 58.3 years. The ethnic distribution was 75.7% White, 15.6% Black, and 3.6% Hispanic or Latino. By 2019, the percentage of female patients increased to 9.3%, with an average age of 56.7 years. The ethnic breakdown changed to 68.1% White, 18.2% Black, and 6.5% Hispanic or Latino.
- Focusing on those with chronic pain, 7.1% were female with an average age of 57.2 years. The ethnic distribution was 74% White, 17.8% Black, and 3.9% Hispanic or Latino. By 2019, the percentage of female patients rose to 12.4%, with the average age remaining at 57.2 years. The ethnic distribution shifted to 65.3% White, 21.9% Black, and 7.0% Hispanic or Latino.
- In patients with chronic pain, since the introduction of medical cannabis laws (MCL), there has been a 0.135% (95% CI 0.118 to 0.153) increase in cannabis use disorder prevalence.
- Since the introduction of recreational cannabis laws (RCL), there has been a 0.188% (95% CI 0.160 to 0.217) increase in cannabis use disorder prevalence.
- Interestingly, in patients who do not have chronic pain, since the introduction of MCL and RCL, there have been smaller increases in cannabis use disorder prevalence (MCL: 0·037% [0.027 to 0.048], 5.7%
Overall, Hasin and colleagues (2023) found that the associations of MCL and RCL with cannabis use disorder was greater in patients with chronic pain than those without. However, the increase observed was only a fraction of a percentage point.
Hasin and colleagues (2023) found that those with chronic pain had significantly larger increases in cannabis use disorder due to the introduction of MCL and RCL. The authors also noted significant increases in cannabis use disorder in older age groups since the introduction of these laws. This led the authors to conclude that MCL and RCL are likely to increase the prevalence of cannabis use disorder, and the commercialisation has resulted in improved access.
Strengths and limitations
This study had several strengths. Notably, this is the first study to explore differences in the relationship between MCL, RCL and the impact on cannabis use disorder prevalence in the context of chronic pain status. The study examined a large cross-sectional cohort, with data collected over a longitudinal period of 15 years. This meant that time-varying incremental changes could be assessed. Overall, the study has an important place in adding to the evidence base about older patients with chronic pain and increasing prevalence of cannabis use.
There are several limitations to the current paper. As most patients in the VHA are largely White, male and in the 65-75 age bracket, they are not representative of veterans broadly or of the general population. The sample characteristics may limit the generalisability of findings more widely. Additionally, there was a high bar for the diagnoses for cannabis use disorder. This is because the diagnoses were made by clinicians who most often diagnose severe disorders and may have missed sub-clinical cases which otherwise may have been picked up by sensitive structured assessments. Furthermore, the time lag effect of law implementation should be considered as it is likely that the effect of such laws takes time to emerge. The authors analysed time lags of 1 year to ensure that as many RCL states could be included in the analysis as possible, as for many, these were implemented in recent years. As time progresses and more data is available, longer time lags should be analysed to examine delayed effects of the impact of law changes.
Implications for practice
This study has key implications within policy, clinical care, and research. The authors demonstrated that the prevalence of cannabis use disorder with chronic pain is increasing disproportionally, particularly in older adults following state legislation. As such, reducing the risk of harm associated with this public health concern is essential but in proportion to other health needs.
It is suggested that older patients with chronic pain who use cannabis should be closely monitored by their treating clinicians and be made aware of the risks of cannabis use disorder and alternative treatments. This is particularly pertinent for patients residing in states where cannabis use has been legalised who may be more vulnerable to cannabis use disorder. In a UK context, medical cannabis was legalised in 2018 under specific circumstances but yet no work exists to explore the impact of this legalisation. This may be a unique opportunity to explore implications for future practise.
Research should be conducted monitoring the short-term and long-term harms associated with cannabis use disorder, particularly in those with co-morbid conditions such as chronic pain. This should be communicated to policy makers, clinicians and the general public, to provide unbiased scientific evidence, unadulterated by competing public health and commercial interests.
Cannabis in the United States is a multibillion-dollar industry, with increasingly positive public beliefs about its safety and efficacy. Often companies distributing medicinal cannabis advertise unsubstantiated claims about the safety and efficacy of their product, encouraging greater demand. Public health campaigns discussing the risk of cannabis use disorder in those with chronic pain and the associated harms are required.
Statement of interests
Grace Williamson and Daniel Leightley are currently undertaking a study exploring the use of cannabis in association with PTSD symptoms in the United States and United Kingdom in collaboration with University of Southern California and RAND Corporation. Further, Daniel Leightley is an Army reservist in the United Kingdom Armed Forces and this review has been undertaken as part of his civilian employment.
S. Hasin et al., “Chronic pain, cannabis legalisation, and cannabis use disorder among patients in the US Veterans Health Administration system, 2005 to 2019: a repeated, cross-sectional study,” The Lancet Psychiatry, vol. 10, no. 11, pp. 877–886, Nov. 2023, doi: 10.1016/S2215-0366(23)00268-7.
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