Introduction 

Cannabis is a commonly used drug across the globe. In 2017, the WHO estimated that there were 147 million consumers of cannabis, equivalent to 2.5% of the world’s population.1 The legal environment for use of cannabis, for either medicinal or recreational purposes, is rapidly evolving and in a number of jurisdictions, becoming less restrictive.

The long-term health impacts of chronic cannabis use are unclear.2 A recent report by the National Academies of Science, Engineering and Medicine suggests that there is substantial evidence that chronic cannabis smoking is linked to poorer respiratory health, lower birth weight of offspring born to mothers who smoke cannabis during pregnancy; in addition, there is a greater likelihood of the development of psychotic disorders among heavy users.3 Risk factors for developing problematic cannabis use include earlier age of cannabis use, being male and smoking tobacco cigarettes.3

With the rise in the number of jurisdictions, both subnational and national, in legalisation of cannabis, it is important to measure and understand the interactions between cannabis and tobacco use (especially cigarettes). Existing evidence shows that co-occurring use of tobacco and cannabis (‘co-use’) is widespread, with as many as 90% of cannabis users reporting a history of tobacco smoking.4 Co-use of these substances can take several forms, including concurrent use of tobacco and cannabis (ie, ‘dual users’ of both substances). Co-administration through use of ‘blunts’ (cigar wrappers partially or fully emptied and replaces with cannabis), ‘spliffs’/‘mulled cigarettes’ (joints filled with tobacco and cannabis), or waterpipes is commonplace, with use of mulled cigarettes being significantly more common in areas outside of the USA.5 More recent reports suggest low-level prevalence of co-use occurs by the delivery of cannabis plant material and/or concentrates via personal vaporisers and electronic nicotine delivery systems such as e-cigarettes.6 7 Chronic co-use is associated with greater dependence on both substances,5 8 greater difficulty in quitting cannabis,5 8 and potentially increased health risks.3 7 As more jurisdictions permit medicinal and/or recreational cannabis sales, examining tobacco-cannabis associations and co-use becomes particularly relevant due to the prospect of increasing cannabis use9 and potentially, tobacco product use and dependence.

In 1976, the Netherlands was among the first countries to relax restrictions on cannabis use through revisions to its Opium Act, in conjunction with government decisions to discontinue prosecuting cannabis-related offences under specific circumstances.10 During this time, the Netherlands introduced its coffee-shop model, which permitted such establishments to sell cannabis in small quantities for personal consumption. Coffee shops are subject to numerous restrictions, including bans on the sale of alcohol, hard drugs (such as heroin, cocaine, amphetamine, ecstasy and GHB), advertising, youth sales and restrictions on the quantity of cannabis sold per day as well as intolerance of public nuisances.11 Use of tobacco is not permitted in coffee shops, although most have a designated section where smoking is allowed, in accordance with the current Dutch tobacco law, which permits smoking in separately ventilated smoking sections in hospitality industry venues.11

This study examined co-use of cannabis and tobacco in a country where cannabis use is legal. The objectives were to examine predictors of current cannabis use and characterise methods of consumption among smokers and non-smokers.

Methods

Results

Past 30-day cannabis use and cigarette smoking status. Cigarette use was split between primary FM (51.2%) and primary RYO (44.8%). Past 30-day use of cannabis use was substantially higher among current cigarette smokers (n=57/987=5.8%) than among former or never smokers (n=10/288=3.5% and n=6/316=1.9%, respectively) (X2(2)–9.22, p=0.010). There was evidence for marginally higher cannabis use among FM compared with RYO smokers (7.3% vs 4.3%, p=0.087). Table 1 illustrates the factors independently associated with current cannabis use. Current cigarette smoking was the strongest predictor of cannabis use (OR=4.13). Older respondents (aged 25+) were less likely to use cannabis (OR=0.36). We saw no differences in use by sex, income or education (all p<0.08).

Cannabis consumption methods and cigarette smoking status

Among cannabis users, joints were by far the most prevalent use method for both current tobacco (or cigarette) smokers (96.9%) and non-smokers (comprised of former and never smokers) (76.5%). Among cannabis users, waterpipe was the use method for 8.8% of current smokers and 12.5% of non-smokers. Using a vaping product was the use method for 5.3% of smokers and 0% of non-smokers. Among those who used joints, nearly all current smokers (94.6%) and 2/3 of non-smokers (66.7%) reported ‘always’ rolling cannabis with tobacco when they used cannabis (see figure 1). There was no difference between mostly FM made cigarette users and mostly RYO users in whether they ‘always’ roll tobacco with cannabis (93.8% vs 95.2%, respectively; p=0.903).

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Figure 1

Per cent reporting rolling tobacco with cannabis among past 30-day cannabis users (n=68); X²=8.70; p=0.013.

Discussion

This study collected data from 1599 participants, including current cigarette smokers, former cigarette smokers and never cigarette smokers, which allowed for a measure of potential misclassification in terms of accrual exposure to nicotine and tobacco smoke. In this Netherlands-based sample, most cannabis was reported to be consumed via smoking joints, most often mixed with tobacco. The practice of mixing cannabis with tobacco is consistent with data from other European countries.14–16 This behaviour may present unique health concerns for non-cigarette smoking cannabis users, since they are being exposed to tobacco, and that exposure could lead to nicotine dependence. Moreover, many non-cigarette smoking cannabis users appear to be misclassified as to their actual tobacco/nicotine exposure.

Although the sample size in this study was small, a high proportion of self-reported non-cigarette smokers reported always (66.7%) or sometimes (16.7%) rolling cannabis with combustible tobacco for consumption. This means that many non-cigarette smoking cannabis users are likely misclassified as to their actual tobacco/nicotine exposure in surveys. This has importance in terms of future research when considering the precision with which we measure tobacco use and cannabis use separately and together. Future studies should take into account the potential that cannabis users are being exposed to tobacco through joints but might not identify as tobacco users in a survey.

With respect to public health considerations, mixing tobacco with cannabis increases tobacco smoking among current cigarette smokers and might work to promote tobacco related toxicant exposure and nicotine dependence among non-cigarette smokers. Qualitative work15 has suggested as much as 50% of a mulled cigarette consists of tobacco, which represents a significant opportunity for nicotine exposure among those who otherwise may not consider using tobacco or other nicotine-containing products to a substance with known addictive properties. Considering the relative differences in perceived harms17–19 for smoking cannabis in contrast to smoking cigarettes, further studies should work to disentangle how such perceptions may influence co-use and design studies that would allow for a more precise measurement of exposure and dependence among cigarette smokers and non-cigarette smokers who engage in this type of consumption in various policy contexts.

A limitation of this study is the low-sample size of overall past 30-day cannabis users and non-cigarette smoking cannabis users limits the generalisability of the results, as well as the ability to conduct more sophisticated data analysis in terms of consumption methods and use patterns.

Further research is needed to examine the impact of mixing tobacco and cannabis on important outcomes such as the development of nicotine dependence and prospective sustained tobacco consumption.