Long-term cannabis use and preparedness for ageing

The longitudinal study by Madeline H Meier and colleagues1Meier MH Caspi A Ambler A et al.Preparedness for healthy ageing and polysubstance use in long-term cannabis users: a population-representative longitudinal study.Lancet Healthy Longev. 2022; 3: 703-714Summary Full Text Full Text PDF Scopus (1) Google Scholar on the preparedness for healthy ageing and polysubstance use in people with long-term cannabis use, published in The Lancet Healthy Longevity, reports on a topic about which relatively little is known—ie, the effects of long-term cannabis use on mid-life ageing indicators, including biological ageing, and health, financial, and social preparedness for old age. The study makes use of the Dunedin longitudinal cohort, which has been followed up repeatedly up to age 45 years. Findings showed that people with long-term cannabis use had worse outcomes than those who had never used cannabis on measures of biological ageing, health preparedness, financial preparedness, and social preparedness. However, given that use of multiple substances was common among individuals who used any one substance, the study also addressed the challenge of polysubstance use by analysing the outcomes in people with long-term cannabis use and comparing them with outcomes of those who had never used cannabis, those with long-term tobacco use, long-term alcohol use, and mid-life recreational cannabis use, and those who had quit using cannabis before age 45 years. Analyses specifically addressing polysubstance use compared long-term cannabis use with long-term alcohol use and long-term tobacco use, and also examined dose–response associations for persistent dependence on each substance after accounting for persistent dependence on the other substances. Results indicated that multiple substance use and substance dependence accounted for the findings on biological ageing, health preparedness, and financial preparedness rather than cannabis use alone. However, cannabis dependence itself remained robustly related to poorer midlife social preparedness, particularly social support. In many ways, the design of this important study is exemplary: a prospective study of people with cannabis use who were repeatedly assessed for substance use and other relevant variables throughout their lives. The study design overcomes methodological concerns regarding cross-sectional studies on similar topics in middle-aged samples based on one-time retrospective reports of cannabis and other substance use or substance use disorders over the lifecourse, which are susceptible to memory problems and might seriously underestimate lifetime rates compared with studies that prospectively assess participants repeatedly as they age.2Moffitt TE Caspi A Taylor A et al.How common are common mental disorders? Evidence that lifetime prevalence rates are doubled by prospective versus retrospective ascertainment.Psychol Med. 2010; 40: 899-909Crossref PubMed Scopus (624) Google Scholar The comparison groups were chosen with care and provide an excellent basis for evaluating the effects of long-term cannabis use relative to long-term use (or absence of use) of other substances. The authors controlled for many relevant variables, and also conducted e-tests to determine whether their results could be accounted for by unmeasured confounding. Their conclusions on polysubstance use take appropriate account of the results. Of course, no single study can address all questions, and some questions remain, such as whether the use of illicit substances or non-medical use of prescription medications (eg, opioids or stimulants) would have affected the outcomes. The study also did not address whether the presence or absence of mental health conditions would have affected the results. Many studies have shown that other substance use and mental disorders are more prevalent among people who use cannabis and among those with cannabis use disorder than in others with no substance use disorder,3Hasin DS Kerridge BT Saha TD et al.Prevalence and correlates of DSM-5 cannabis use disorder, 2012–2013: findings from the National Epidemiologic Survey on Alcohol and Related Conditions–III.Am J Psychiatry. 2016; 173: 588-599Crossref PubMed Scopus (363) Google Scholar so these conditions will be important to include at some point if numbers permit. Also, as the authors note, the tetrahydrocannabinol potency of cannabis has increased considerably over the past few decades;4Chandra S Radwan MM Majumdar CG Church JC Freeman TP ElSohly MA New trends in cannabis potency in USA and Europe during the last decade (2008–2017).Eur Arch Psychiatry Clin Neurosci. 2019; 269: 5-15Crossref PubMed Scopus (287) Google Scholar therefore, cohorts beginning their cannabis use more recently than the cohort studied are likely to be using much more potent cannabis products, which could potentially yield different results. In addition, the norms and legal status of cannabis are undergoing marked changes in many countries. These changes include the increasing perception that cannabis can be used without risk of adverse consequences, including among older adults,5Han B Sherman S Mauro PM Martins SS Rotenberg J Palamar J Demographic trends among older cannabis users in the United States, 2006–13.Addiction. 2017; 112: 516-525Crossref PubMed Scopus (158) Google Scholar and that such use is beneficial for many health and medical reasons—a perception that is encouraged by the growing cannabis for-profit industry, with some claims made without a scientific basis. Concomitantly, legalisation of cannabis use for medical and also recreational use is growing in states in the USA, and also in other countries (eg, Canada, Uruguay, Malta, and South Africa). How all these changes will affect the consequences of long-term cannabis use is presently unknown and remains to be shown by future research studies. In the context of other studies, the present study by Meier and colleagues1Meier MH Caspi A Ambler A et al.Preparedness for healthy ageing and polysubstance use in long-term cannabis users: a population-representative longitudinal study.Lancet Healthy Longev. 2022; 3: 703-714Summary Full Text Full Text PDF Scopus (1) Google Scholar is consistent with findings from a nationally representative US sample of 14 715 adults aged 50 years or older showing an association of cannabis use and cannabis use disorder with lower perceived social support, even when controlling for other risk factors including use of other substances and psychiatric disorders.6Choi NG DiNitto DM Marti CN Older marijuana users: life stressors and perceived social support.Drug Alcohol Depend. 2016; 169: 56-63Crossref PubMed Scopus (24) Google Scholar These findings were interpreted as indicating the need to develop intervention strategies to address the needs of older adults for better social support, and to reduce their marijuana use.6Choi NG DiNitto DM Marti CN Older marijuana users: life stressors and perceived social support.Drug Alcohol Depend. 2016; 169: 56-63Crossref PubMed Scopus (24) Google Scholar However, findings from Meier and colleagues’ study1Meier MH Caspi A Ambler A et al.Preparedness for healthy ageing and polysubstance use in long-term cannabis users: a population-representative longitudinal study.Lancet Healthy Longev. 2022; 3: 703-714Summary Full Text Full Text PDF Scopus (1) Google Scholar diverged from findings in another study of the Dunhedin cohort on long-term cannabis use and cognitive decline.7Meier MH Caspi A Knodt AR et al.Long-term cannabis use and cognitive reserves and hippocampal volume in midlife.Am J Psychiatry. 2022; 179: 362-374Crossref PubMed Scopus (19) Google Scholar This study found that long-term cannabis use was associated with many aspects of cognitive decline from childhood to midlife, and with informant-reported memory and attention deficits.7Meier MH Caspi A Knodt AR et al.Long-term cannabis use and cognitive reserves and hippocampal volume in midlife.Am J Psychiatry. 2022; 179: 362-374Crossref PubMed Scopus (19) Google Scholar In contrast with Meier and colleagues’ study on preparedness for healthy ageing,1Meier MH Caspi A Ambler A et al.Preparedness for healthy ageing and polysubstance use in long-term cannabis users: a population-representative longitudinal study.Lancet Healthy Longev. 2022; 3: 703-714Summary Full Text Full Text PDF Scopus (1) Google Scholar in which many of the outcomes were better accounted for by polysubstance use than by cannabis use alone, the findings on cognitive deficits were specific to people with long-term cannabis use7Meier MH Caspi A Knodt AR et al.Long-term cannabis use and cognitive reserves and hippocampal volume in midlife.Am J Psychiatry. 2022; 179: 362-374Crossref PubMed Scopus (19) Google Scholar because they were either not present or were smaller among people with long-term tobacco use and long-term alcohol use. The findings on manifestations of cognitive decline specifically attributed to long-term cannabis use are important because such deficits predict dementia in older adults,8Scott EP Brennan E Benitez B A systematic review of the neurocognitive effects of cannabis use in older adults.Curr Addict Rep. 2019; 6: 443-455Crossref PubMed Scopus (17) Google Scholar a problem that is growing in prevalence and in seriousness to society given the ageing populations of many countries. The findings reported by Meier and colleagues1Meier MH Caspi A Ambler A et al.Preparedness for healthy ageing and polysubstance use in long-term cannabis users: a population-representative longitudinal study.Lancet Healthy Longev. 2022; 3: 703-714Summary Full Text Full Text PDF Scopus (1) Google Scholar showing that long-term cannabis use specifically predicts worse social preparedness have important implications. People with long-term cannabis use had significantly worse social support than the other groups, findings that remained robust after analytically addressing the use of other substances. These findings suggest that attention to lack of social support among middle-aged and ageing individuals with long-term cannabis use is warranted. For health and mental health professionals, this focus could include helping patients develop better social supports and stronger social networks to provide positively reinforcing activities other than cannabis use. For research purposes, given the role of social support in healthy ageing, measures of social support should be included in studies of individuals who use cannabis across all life stages, including among younger people and those in middle age, to learn more about the life-stage trajectories of social support among people who use cannabis. Finally, research explaining the mechanisms giving rise to poor social support among individuals who use cannabis is needed to help develop effective prevention and treatment measures. I declare no competing interests. Preparedness for healthy ageing and polysubstance use in long-term cannabis users: a population-representative longitudinal studyLong-term cannabis users are underprepared for the demands of old age. Although long-term cannabis use appears detrimental, the greatest challenge to healthy ageing is not use of any specific substance, but rather the long-term polysubstance use that characterises many long-term cannabis users. Substance-use interventions should include practical strategies for improving health and building financial and social capital for healthy longevity. Full-Text PDF Open Access

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