A cocktail of caffeine and alcohol can have dangerous repercussions.
The growing popularity of mixed drinks like the "Jager Bomb" (Jagermeister and Red Bull) or "Vodka and Red Bull" can have implications on road safety, according to the study.
The field study of over 800 young drinkers by the University of Florida found that those who consumed caffeine-alcohol mixed drinks were often in a drunker state when they left the bar than those who consumed only alcohol-based drinks.
Those who had caffeine-alcohol mixed drinks were also much more likely to say they intended to drive home.
The problem arises from consuming a stimulant alongside an intoxicant, which, clinical studies show, can reduce the perception of being drunk but not the impairment.
For the study, researchers wandered on the streets outside bars and clubs, from 10pm to 3am, to quiz young drinkers on what they had been drinking and assess their sobriety, reports News.com.au.
According to the study: "Patrons who had consumed alcohol mixed with energy drinks were at a three-fold increased risk of leaving a bar highly intoxicated.
"... As well as a four-fold increased risk of intending to drive on leaving the bar district, compared to other drinking patrons who did not consume alcoholic beverages mixed with energy drinks."
Consuming these drinks with alcohol was emerging as a cause of "elevated involvement in night-time risk-taking behaviour"
The study has appeared in the journal of Addictive Behaviors.