The research, which was published this month in the journal Addiction, found that combined tobacco and alcohol use cost more than a quarter of a billion disability-adjusted life-years worldwide. Illegal drugs on the other hand, only accounted for tens of millions. A disability-adjusted life year, according to the study, represents the number of years lost due to ill health, disability or early death.
"These findings are not surprising given that legality of the drugs coincides with social norms around drug use as well as use prevalence," Dr. Carla J. Berg, an associate professor in the Department of Behavioral Sciences and Health Education at the Rollins School of Public Health of Emory University, told the Atlanta Journal-Constitution.
Globally, one in five adults reported at least one occasion of heavy drinking in the past month and one in seven smokes tobacco, according to the 2015 data used for the study. Conversely, fewer than one in 20 people worldwide were estimated to use illicit drugs in the past year, including amphetamines, opioids, marijuana and cocaine.
But study co-author Dr. Robert West of University College London pointed out that the United States and Canada had among the highest rates of dependence on opioids (650 cases per 100,000), cocaine (301 cases per 100,000) and marijuana (749 cases per 100,000 people), according to U.S. News and World Report. Overall, the rates of marijuana and opioid dependence were about three times higher than the rest of the world.
"The U.S. has major research agendas moving forward to advance our knowledge-base in order to inform policy and practice regarding how to best address this problem," Berg said. "Surveillance is a key part of monitoring the problem, informing interventions, and evaluating policies and practices that are adopted and implemented."
Berg said that broad international studies, such as this one, help researchers better understand differences in drug use across countries.
"Not all countries regulate alcohol and tobacco in similar ways nor have policies or practices in place that aim to address specific aspects of behavior related to alcohol and tobacco use," Berg said.
"Social norms are also quite different in relation to the use of these substances, particularly among different genders within a country or within other sub-populations," she explained. "Understanding these different multilevel factors and their impact on alcohol- and tobacco-related consequences are key to informing how countries like the U.S. should address this critical issue."
Berg adds that this kind of study is "critical" in helping researchers and governments understand the societal and individual costs of substance abuse. It also gives a better picture of how legalization and regulation impact usage and dependence.
"There could be a great deal to be learned from countries or areas of the world with lower prevalence of opioid dependence and areas of the world that have combated opioid dependence successfully," she said. "This speaks to how critical international research is to informing policy and practice."