Excessive alcohol use and persistent smoking have both been found independently to have a deleterious impact upon prospective memory (PM: memory for planning and executing future activities) and executive function (EF: the control of attention in memory) in the past.

The present study examined whether those who simultaneously drank alcohol and smoked were at greater risk of PM and EF deficits compared with an alcohol-only group and a zero-substance user group.

Anyone reporting using illegal substances (e.g. ecstasy/cannabis) were excluded. 23 poly-drug users (PD: those who drank and smoked), 27 single drug users (SD: who only drank alcohol) and 29 zero-users (ZU: who did not use any recreational drug) were compared on measures of anxiety, depression, PM and EF. PM was measured using a virtual reality PM task (VRPMT) in which the participant had to recall specific activities at particular locations when navigating though the computer-based virtual reality ‘office’ environment. EF was measured using the Reverse Digit Span (RDS) which required the participant to recall increasing numbers of digits in reverse order.

There were no significant between-group differences in terms of gender, age, alcohol use (PD and SD only), anxiety, or depression scores. The PD group performed the worst on the VRPMT and RDS tasks; followed by the SD group; with highest performance on these tasks being observed in the ZU group.

Combined drinking and smoking produces a kind of ‘double whammy effect’ on PM and EF, compared with single drug-use and zero-user groups.