The last quarter century has witnessed rapid expansion in legal access to cannabis for medical and recreational purposes. Downstream effects have impacted all age groups, although major research gaps persist on the benefits and risks of cannabis use, especially regular or heavy use, for many populations, including older adults. While a growing evidence base suggests cannabis use can relieve neuropathic pain and spasticity, clinicians are hamstrung by a lack of data on side effects, especially for older populations with more medical comorbidities and polypharmacy. Guidelines are needed for screening and treating cannabis use disorder in older populations.
cannabis, older adults, side effects, cannabis use disorder
Recent decades have witnessed dramatic expansions in legal cannabis access for medical and recreational purposes (Williams et al., 2016). Rates of cannabis use, including daily or near daily use, have risen notably in adult and older adult populations (Williams et al., 2017). Cannabinoids are products derived from the cannabis plant, typically featuring either delta-9-tetrahydrocannabinol (THC) or cannabidiol (CBD), although more than 100 cannabinoids have now been identified. Between whole plant smoked or vaped cannabis and cannabinoid derivatives (edibles, tinctures, beverages, and topicals), many older Americans now have access to an entire array of cannabis products, often with much higher potency than the drugs accessed in their youth (Chandra et al., 2019; Mehmedic et al., 2010).
As of the November 2018 election, ten states and Washington, DC, had passed laws allowing both medical and recreational use of cannabis (National Council of State Legislators [NCSL], 2018), and an additional twenty-three states (NCSL, 2018) allowed for medical cannabis programs of varying design (Williams et al., 2016). With expanded legal access to cannabis, there has been growing concern that increased availability could lead to unintended harms differentially impacting various subpopulations. While acute concerns often focus on teens and younger adults, paradoxically, studies have shown the greatest increases in rates of cannabis use among older adults (Williams et al., 2017).
With expanded access, all age groups report higher rates of heavy use (i.e., daily or near daily use) than in the past (Hasin et al., 2017), and once rare clinical presentations (such as cyclic vomiting syndrome) are becoming more common. Also, greater surveillance is needed for public hazards from public intoxication such as drugged driving, especially among users who mix cannabis with even minimal amounts of alcohol (Volkow et al., 2014).
The National Academies of Sciences, Engineering, and Medicine (NASEM) in 2017 published an update to the Institute on Medicine’s 1998 report cataloging potential evidence-based indications for the medical use of cannabis. In the late 1990s, states had only just begun to allow legal use of cannabis, in addition to FDA-approved pharmaceuticals already on the market for nausea and vomiting and AIDS-related cachexia, notably Marinol, a synthetic analog to the cannabinoid THC. Of note, twenty years later, the emerging strongest evidence for the medical use of cannabis was for chronic pain, especially neuropathic pain, and spasticity, such as is common in multiple sclerosis (NASEM, 2017; Whiting et al., 2015).
With advancing age, older adults are more sensitive to the potential side effects of cannabis because of the altered pharmacokinetics and pharmacodynamics associated with normal aging (see Table 1). The distribution and elimination of cannabis in older users are due to a multitude of mechanisms summarized in Table 1. These include an increased volume of distribution due to increased body fat and reductions in lean mass, reduced hepatic blood flow and clearance leading to higher plasma concentrations, which are often especially pronounced in older adults using multiple prescription medications, and declining organ function in other systems.
Table 1: Physiologic Changes and Effects of Natural Aging on Cannabis
|Physiologic Changes||Clinical Implications|
Alongside the nation’s aging population, there is growing concern about the under-diagnosis of substance use disorders among older adults, including cannabis use disorder. Earlier this year, the U.S. Preventive Services Task Force announced revisions to its previous guidelines, and now recommends screening all adults in primary care services for drug use. This guideline explicitly states that screening can be conducted with verbal or written questionnaires (rather than drug testing) and should only occur when referrals to evidence-based treatment are available (Williams and Levin, 2020). Despite this new guideline, screening is infrequent and treatment of substance use disorders among older adults remains inadequate.
Unfortunately, there is no gold standard for adapting substance use disorder screening for older patients (Galanter, Kleber, and Brady, 2015), who may have more physical comorbidities and may be less likely to be working than younger patients. Clinicians should prioritize assessing for any dysfunction in domains of a patient’s day-to-day life: for example, interference with social activities, instead of problems on the job. Conversely, older adults may be prone to physical side effects and medical problems complicated by regular or heavy cannabis use and drug-drug interactions (e.g., injuries), even in the absence of a primary cannabis use disorder. If diagnosed, patients with cannabis use disorder should be referred to quality programs that offer models of psychotherapy, behavioral, and pharmacologic treatments for cannabis use disorder (Williams and Hill, 2020). Given the high rates of other chronic medical conditions, it is helpful if the treatment programs have medical and nursing staff.
While the media and people in the cannabis industry tout the potential benefits of cannabis for almost any conceivable indication, high quality data remain limited to a few indications and are largely unable to provide tailored dosing recommendations for a given patient or population, such as older adults. Clinicians are advised to counsel patients on these risks and maintain a therapeutic rapport, which could allow for intervention if patients develop problems with side effects or addiction with cannabis-based products.
Author’s Note: This work was funded by NIDA R21 DA045267 (Williams).
Arthur Robin Williams, MD, MBE, is an assistant professor of clinical psychiatry at Columbia University Division on Substance Use Disorders and research scientist at the New York State Psychiatric Institute, both in New York City.
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