Medicinal Use of Cannabis and Cannabinoids in Older Adults: Where Is the Evidence?

Marijuana (Cannabis sativa) has been used medicinally for centuries for the management of different conditions and diseases.1 The cannabis plant contains a number of cannabinoids, which are responsible for its physiological and psychoactive effects. They act primarily through CB1 (brain) and CB2 (peripheral organs and tissues) receptors. The use of medicinal cannabis is increasing in older adults, but the exact prevalence of cannabis use is not known. A recent survey by the International Association for Cannabinoid Medicines on the medicinal use of herbal cannabis (marijuana) and cannabinoid-based medicine, completed by 953 participants from 31 countries (e.g., United States, Germany, Canada, France, the Netherlands), showed that 6.5% of medicinal cannabis users were aged 61 to 76.2 In the Netherlands, between 2003 and 2010, 37% of 5,540 patients who used prescription herbal cannabis were aged 61 to 93.3 Although the medicinal use of cannabis and cannabinoids in the general population has been debated recently, there has been no discussion of the use of cannabis by older adults, a growing population of users. In a survey, 1,099 of 1,446 (76%) readers of the New England Journal of Medicine agreed with the medicinal use of marijuana by a 68-year-old woman with metastatic breast cancer, nausea, pain, and fatigue,4, 5 but different arguments were used to support this treatment, and none specifically referred to frail older adults. Several randomized clinical trials have demonstrated the therapeutic benefits of cannabis and cannabinoids in the management of pain and nausea, but most of these trials did not include older adults, or if such individuals were included, separate analyses were not performed.6-9 Older adults are a vulnerable group because of age-related physiological changes and a high prevalence of comorbidity and polypharmacy, which increase the likelihood of adverse drug events.10 Thus the data on safety and efficacy of cannabis reported in trials with young adults cannot be extrapolated to frail older adults. Moreover, various factors such as the illegal status of cannabis in many countries, social stigma, smoking as route of administration, uncertain dosage, and dependency, limit the prescription of medicinal cannabis to this population. There are two oral cannabis-based drugs available in tablet form (dronabinol and nabilone) and one in-mouth spray form (nabiximols). Dronabinol and nabilone (tetrahydrocannabinol) are registered in some countries, including the United States, for stimulating the appetite in individuals with acquired immunodeficiency syndrome–related anorexia or chemotherapy-induced nausea and vomiting. Nabiximols, a combination of THC and cannabidiol, is registered in some European countries and Canada (but not in the United States) for the treatment of spasticity and pain in multiple sclerosis. According to the knowledge of the authors of this letter, only two randomized clinical trials have exclusively included older adults. The first trial reported that dronabinol (2.5 mg/d) appeared to be effective in the treatment of anorexia and behavioral disturbances in individuals with severe Alzheimer's disease (n = 12; 11 male; mean age 72.7),11 and the second reported that dronabinol (2.5 mg/d) reduced nighttime agitation in individuals with Alzheimer's disease (n = 2; 75- and 81-year-old men).12 Neither trial reported serious treatment-related adverse reactions, but the small number of participants resulted in insufficient power to draw firm conclusions about the benefits of medicinal cannabis. Although several studies have investigated the pharmacokinetics and routes of administration of cannabis and cannabinoids in the general population, only one study has evaluated the pharmacokinetics of THC in older adults.13 The lack of information about the safety and efficacy of cannabis and cannabinoids in older adults warrants further research, especially adequately powered randomized controlled trials to assess the evidence for, and the risk–benefit ratio of, medical cannabis in older individuals. Until then, individual evaluation of the pros and cons is necessary before cannabis can be prescribed to older adults. Conflict of Interest: None of the authors has any conflict of interest, financial or otherwise. Author Contributions: All authors contributed equally to this letter. Sponsor's Role: None.