Consequences of concurrent amphetamine-type stimulant (ATS) and alcohol use by young adults: Offending behaviour, victimisation and other harms

In 2009, the young adult cohort for the Natural History Study of Drug Use (NHSDU) was recruited, comprising regular amphetamine-type stimulant users (i.e. ecstasy or methamphetamine; n=352) and a comparison group of non-users (n=204). Information on offending behaviour was collected at the 4 ½ year follow-up, when participants were aged 24 to 27 years. At this stage, around half of the ATS users had recently used ecstasy and one-quarter had recently used methamphetamine (i.e. in the last 12 months). Despite decreases in the quantity of alcohol consumed on a typical drinking occasion, the quantity consumed concurrently with ATS remained high after 4½ years (55% of males and 13% of females consumed > 10 standard drinks on last occasion of ecstasy use). Compared to non-users, significantly greater proportions of ATS users created a public disturbance under the influence of alcohol in the past 12 months (males: 18% vs. 2%; females: 13% vs. 1%). ATS-using drivers were more likely than their non-using counterparts to engage in drink-driving or speeding. These behaviours contributed to crashes. Further, about one quarter (24%) of ATS users had a lifetime diagnosis of conduct disorder, compared to 9% of non-users. At the 12 month study follow-up, ATS users with a history of conduct disorder were more likely than other users to have recently verbally abused (32% vs. 19%) or physically abused (12% vs. 3%) someone. However, rates of antisocial behaviour decreased significantly after 4½ years. Methamphetamine was more strongly linked with antisocial behaviour than ecstasy use. A number of factors increased the likelihood of aggression in methamphetamine users, including high-dosage methamphetamine use, concurrent use of large quantities of alcohol, and a predisposition toward aggression. Frequent methamphetamine users were more engaged with drug dealers than other ATS users. Dealing ATS was associated with substance-related police contact, being charged with a drug-related offence, using higher quantities of ATS across 4½ years, and using a larger range of illicit drugs. Compared to non-users, ATS users had higher rates of ‘intensive’ police contact (e.g. being detained by police) related to their use of alcohol or illicit drugs (ATS users: 46.3%; non-users: 10.7%) and significantly lower perceptions of police respect and trustworthiness with regard to this contact. ATS users had lower levels of belief in the legitimacy of police or the law, were less committed to police, had lower support for drug-law enforcement, and were less willing to cooperate with police. However, strong belief in procedural justice was associated with greater willingness to cooperate and greater support for drug-law enforcement. For a small proportion of ATS users, substance-related police contact was seen as a ‘wake-up call’ and was coupled with reduced or more cautious drug use.