What's The Science Behind Caffeinating Cocktails?

As a bartender at a coffee shop/bar hybrid, I’m often asked to mix coffee and booze. Most of the time, it tastes good, but just don’t ask me to reuse your cooled-off partial cup of coffee—it’s a health code violation on soooo many levels.

Mixing caffeine and alcohol isn't new, but the process has garnered a lot of attention as of late. With the recent nationwide ban on various types of alcoholic energy drinks, the interaction between caffeine and ethyl alcohol has received a good deal of academic press.

Cups of Caveats

Caffeine may be the most studied drug in history, but the mechanics of how the molecule interacts with other substances is still largely theoretical. Outside of social/behavioral studies, the combination of booze and caffeine is especially hard to study because researchers can’t ethically give their subjects as much booze and/or caffeine as it would take to mimic real world binge drinking.

As a result, subjects can only consume moderate amounts of each. At these levels, it appears that they may feel drunk, but their reaction times aren’t significantly different from subjects given the placebo.

[Safety Note: If you’re going to experiment on your own, be careful. This should go without saying, but never drink and drive. The combination of caffeine and alcohol may make you feel less drunk, but your blood alcohol content (BAC) still works like you’re only drinking booze.]

Another challenge in studying the interactions of caffeine and hooch is that the amount of caffeine in any given drink may vary. For example, caffeine levels in coffee depend on how it’s grown, roasted, ground, and prepared.

To complicate things further, energy drinks can vary in size from 1 oz shots to 23 oz cans. Within the size differences, different brands use varying levels of caffeine in similar products. For researchers, the variation means that it’s difficult to figure out how much caffeine causes the manifestation of its negative effects.

Queen Caffeine

We know that all people absorb caffeine in roughly the same way. However, many factors including alcohol, pregnancy, and even grapefruit juice can extend the molecule’s half-life within the body.

We also know that alcohol affects each person differently based on his/her gender, body mass, water content, and food consumption. When drunk together, caffeine can somewhat override the sleepiness and ataxia (lack of voluntary coordination in movement) that come with heavy drinking. Alcohol, in turn, can suppress the anxiety/jitteriness that comes with too much caffeine. What causes these changes is less clear.

Caffeine is known to unselectively block adenosine (a neuromodulator believed to promote sleep and suppress arousal) receptors in the brain. Since alcohol raises the levels of adenosine outside of cells, it would normally cause a drinker to get sleepy. In this article from the Journal of Caffeine Research, researchers posit that caffeine curbs sleepiness and ataxia by blocking a specific adenosine receptor—A1.

Increased levels of adenosine may suppress caffeine’s anxiety-causing compounds. Caffeine may also affect how a slightly different adenosine molecule (A2A), interacts with dopamine receptors to amplify the effects of dopamine released into the brain by alcohol.

Hit the Lab

If you’re going to experiment with mixing these two substances, be careful. Caffeine may exacerbate alcohol’s addictive aspects, so drink in moderation. Be safe, kids.

Irish Coffee

1 oz Irish cream (I prefer Irishman)
1 oz Irish whiskey

Pour ingredients into a mug. Top with coffee or a latte (if you have an espresso machine handy).