Can the gateway hypothesis, the common liability model and/or, the route of administration model predict initiation of cannabis use during adolescence? A survival analysis--the TRAILS study

The co-occurring use and misuse of cannabis and tobacco: a review

AIMS

  Cannabis and tobacco use and misuse frequently co-occur. This review examines the epidemiological evidence supporting the life-time co-occurrence of cannabis and tobacco use and outlines the mechanisms that link these drugs to each other. Mechanisms include (i) shared genetic factors; (ii) shared environmental influences, including (iii) route of administration (via smoking), (iv) co-administration and (v) models of co-use. We also discuss respiratory harms associated with co-use of cannabis and tobacco, overlapping withdrawal syndromes and outline treatment implications for co-occurring use.

METHODS

  Selective review of published studies.

RESULTS

  Both cannabis and tobacco use and misuse are influenced by genetic factors, and a proportion of these genetic factors influence both cannabis and tobacco use and misuse. Environmental factors such as availability play an important role, with economic models suggesting a complementary relationship where increases in price of one drug decrease the use of the other. Route of administration and smoking cues may contribute to their sustained use. Similar withdrawal syndromes, with many symptoms in common, may have important treatment implications. Emerging evidence suggests that dual abstinence may predict better cessation outcomes, yet empirically researched treatments tailored for co-occurring use are lacking.

CONCLUSIONS

  There is accumulating evidence that some mechanisms linking cannabis and tobacco use are distinct from those contributing to co-occurring use of drugs in general. There is an urgent need for research to identify the underlying mechanisms and harness their potential etiological implications to tailor treatment options for this serious public health challenge.

Substance use initiation: the role of simultaneous polysubstance use

INTRODUCTION AND AIMS

Simultaneous polysubstance use (SPU) is a common phenomenon, yet little is known about its role in substance use initiation.

DESIGN AND METHODS

In the present study, 226 cannabis users completed structured interviews about their substance use history. For each substance ever used, participants provided details of their age of first use, their use in the preceding 30 days and whether they co-administered any other licit or illicit substances the first time they used the substance.

RESULTS

For most illicit substances [powder cocaine, crack, amphetamine, methamphetamine, 3,4-methylenedioxymethamphetamine (MDMA; ecstasy), heroin, opium, gamma-hydroxybutyric acid (GHB), ketamine, psilocybin (magic mushrooms), mescaline, phencyclidine (PCP), peyote and inhalants], results showed that a clear majority of participants (≥75%) reported SPU during their first-ever use of the substance. While SPU was less common on occasions of first use of alcohol, tobacco and cannabis, a high proportion of SPU on occasions of first use of 'harder' drugs could be accounted for by the co-use of alcohol, tobacco and/or cannabis.

DISCUSSION AND CONCLUSIONS

Such findings raise the possibility that specific alcohol, tobacco and/or cannabis use episodes might directly contribute to the initiation of new substance use. Understanding the role of SPU on occasions of first use might help better identify risk factors for substance use progression and improve intervention efforts.

Cannabis use stages as predictors of subsequent initiation with other illicit drugs among French adolescents: use of a multi-state model

The aim of this study was to confirm the influence of cannabis use patterns on the probability of initiation with other illicit drugs (OID). A French nationwide retrospective cohort on drug use was reconstituted on 29,393 teenagers. A Markov multi-state model was fitted, modelling all possible pathways from initial abstinence to cannabis initiation, daily cannabis use and OID initiation. The model was adjusted for tobacco and alcohol use. The risk for OID initiation appeared 21 times higher among cannabis experimenters and 124 times higher among daily cannabis users than among non-users. Tobacco and alcohol use were associated with a greater risk of moving on to cannabis initiation (hazard ratio (HR)=1.2 for tobacco initiation, HR=2.6 for daily tobacco use and HR=2.8 for drunkenness initiation). The results of this study provide a confirmation of a stage process in drug use, mediated by cannabis and liable to lead to OID experiment. This is compatible with the literature on the gateway theory, but goes further by modelling the entire sequence of use. OID experiment could be a consequence of initial opportunity to use the more accessible illicit drug, cannabis.