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.