Is marijuana use becoming a ‘gateway’ to nicotine dependence?

Previous studies have documented a reliable pattern for initiating substance use, with many adolescents beginning with nicotine and/or alcohol and progressing to illicit drugs (Kandel 1975). Nicotine is a particularly potent gateway drug for marijuana. Several studies have found cigarette use to precede marijuana initiation, with a higher prevalence of use among smokers compared to the general public (e.g. Lai et al. 2000). However, recent research suggests that a ‘reverse gateway’ effect may occur for some cigarette smokers, with marijuana use preceding tobacco. In this issue, Amos et al. (2004) report on a qualitative study examining the relationships between tobacco and marijuana use among adolescents and young adults in Scotland. A fundamental theme in this report is the link between cannabis use and cigarette smoking, and how this association reinforced nicotine use in general. As Amos and colleagues report, concomitant use of tobacco and marijuana was common. Although tobacco initiation preceded marijuana initiation in most of the sample, a subset of adolescents was introduced to tobacco use through ongoing marijuana use. Ongoing combined use of both substances appeared to foster cigarette smoking when cannabis use was not possible and also interfered with smoking cessation efforts. When marijuana is smoked in a cigarette, rituals associated with using and/or acquiring marijuana appear to serve as reinforcement for tobacco use. This study shows the process by which nicotine and marijuana become paired as well as some of the reasons why smoking cessation may be particularly arduous for these adolescents. Combined use of tobacco and marijuana is a cross-cultural phenomenon. In the United States concurrent use of cigarettes and marijuana is common, as is the use of blunts, marijuana rolled in cigar papers. Once isolated to discrete subcultures in the United States, blunts are becoming increasingly more mainstream and use has escalated since the 1980s (CEWG 2002). Reports from Australia indicate that mixing tobacco with cannabis is widespread, particularly among Aboriginal youth (Burns et al. 2000). Collectively, these studies highlight the universality of this problem in adolescents and introduce another layer of complexity to drug prevention and nicotine cessation efforts in this subpopulation of smokers. There appear to be several reasons why adolescents combine marijuana with cigarettes or cigars. It appears that some adolescents believe that tobacco will enhance or prolong the effect of marijuana (Gross 1998). In addition, practical considerations reinforce this practice. Both blunts and marijuana filled tobacco cigarettes appear ‘legal’, thus facilitating use in a wider range of situations. However, using marijuana with a tobacco product has the undesirable effect of facilitating nicotine use and dependence—and does so by multiple avenues. It is well known that marijuana use is related to decreases in motivation (Schwartz 1987). Combining substances may reduce an individual's motivation to quit while simultaneously increasing their level of nicotine dependence. In addition, adolescents have other issues that may complicate the cessation process, including a myopic view that focuses on short-term reinforcers over the long-term health consequences associated with smoking. All these reasons impact the desire to quit. Given the increase in initiation of marijuana use among adolescents in 1990s (Johnson et al. 2003) and the use of tobacco products in conjunction, it is possible that concomitant use may have the unwanted side effect of higher levels of nicotine dependence in this subpopulation. Sadly, research is lacking in this area. Well-designed studies are needed to determine the frequency of combined use among adolescent as well as adult populations. Although many survey studies ask about tobacco use and marijuana use, we are unaware of any study that directly asks about combined use. More information is needed on risk perceptions related to combined tobacco-marijuana use. For example, do most blunt users consider themselves tobacco users? Also, are combined users more or less dependent on tobacco than other tobacco users? These answers to these and other questions are necessary to understand the need for interventions and to develop innovative prevention and cessation programs that address cigarette smoking within a polydrug using framework.