We tested whether patrons of the night-time economy who had co-consumed energy drinks or illicit stimulants with alcohol had higher blood alcohol concentration (BAC) levels than patrons who had consumed only alcohol.

Street intercept surveys (n = 4227) were undertaken between 9 p.m. and 5 a.m. over a period of 7 months.

Interviews were undertaken with patrons walking through entertainment precincts, queuing to enter venues or exiting venues in five Australian cities.

The response rate was 92.1%; more than half the study sample was male (60.2%) and the median age was 23 years (range 18-72).

Data were collected on demographics, length of drinking session, venue types visited, types and quantity of alcohol consumed and other substance use. A BAC reading was recorded and a subsample of participants was tested for other drug use.

Compared with the total sample (0.068%), illicit stimulant consumers (0.080%; P = 0.004) and energy drink consumers (0.074%; P < 0.001) had a significantly higher median BAC reading, and were more likely to engage in pre-drinking (65.6, 82.1 and 77.6%, respectively, P < 0.001) and longer drinking sessions (4, 5 and 4.5 hours, respectively, P < 0.001). However, stimulant use was not associated independently with higher BAC in the final multivariable model (illicit stimulants P = 0.198; energy drinks P = 0.112). Interaction analyses showed that stimulant users had a higher BAC in the initial stages of the drinking session, but not after 4-6 hours.

While stimulant use does not predict BAC in and of itself, stimulants users are more likely to engage in prolonged sessions of heavy alcohol consumption and a range of risk-taking behaviours on a night out, which may explain higher levels of BAC among stimulants users, at least in the initial stages of the drinking session.