Pull up to a bar on any given night and you might hear people order a combination of alcohol and caffeine to keep the fun going, whether that’s in the form of rum and soda, whiskey and coffee, vodka and an energy drink, or some other concoction meant to deliver the perfect double-buzz.
You might remember that whole controversy around Four Loko, the beverage line behind those infamous caffeinated alcoholic drinks that sparked a craze in the early aughts. Everyone was trying to be very drunk yet also, defiantly, very awake. Soon enough, reports swirled of alarming hospitalizations reportedly linked to the products, especially among underage teens drinking dangerous amounts of the stuff. In 2010, the Food and Drug Administration (FDA) released warnings to Four Loko’s parent company and to companies selling similar offerings, explaining that the agency had never sanctioned the mix of alcohol and caffeine in their beverages. Sales of those products came to a screeching halt. (Four Loko currently states on their website: “Four Loko does not contain caffeine, taurine or guarana. As part of a voluntary product reformulation in 2010, we removed these ingredients.”)
Even so, the alcohol-caffeine combination is still going strong. In fact, one in three young adults surveyed in 2015 had imbibed at least one mixed drink containing alcohol and caffeine in the previous year, according to a National Institute on Drug Abuse survey of 4,000 people between the ages of 19 and 28. Just as enthusiasm surrounding these drinks hasn’t gone away, neither has confusion about the effects that can come with mixing alcohol and caffeine.
So, what actually happens to your mind and body when you mix alcohol and caffeine?
Much like what you were thinking when you texted your ex after happy hour, the mechanisms at play here are something of a mystery. Experts do know, however, that a chemical called adenosine has a lot to do with it.
Adenosine builds up in your brain throughout the day, acting on your central nervous system and helping to regulate wakefulness and sleepiness, alcohol researcher Brandon Fritz, Ph.D, a postdoctoral fellow in the psychiatry department at the Indiana University School of Medicine who studies the neurobehavioral effects of alcohol, tells SELF. “When it reaches high levels, it is one factor that makes you sleepy,” he explains.
Caffeine, a central nervous system stimulant, essentially wards off drowsiness by suppressing rising adenosine levels. “Caffeine works to kick-start your [energy] by blocking adenosine receptors in your brain, stopping that sleepy signal and perking you up,” Fritz says. Caffeine also acts on other parts of your body, like your heart. Side effects of caffeine can include a rapid heartbeat, heightened blood pressure, shakiness, dizziness, and anxiety, according to the U.S. National Library of Medicine. The likelihood of experiencing these symptoms depends on various factors, like how sensitive you are to caffeine and how much you have. That’s why the USDA’s Dietary Guidelines set the upper healthy limit for daily caffeine intake at about 400 milligrams a day, or about three to five eight-ounce cups of coffee, depending on the specific drink.
As a central nervous system depressant, alcohol has a wildly different effect on you than caffeine. First, it causes more adenosine to accumulate in your system, Fritz explains, hence why you might doze off after a few drinks, try as you might to stay awake. Drinking alcohol can also slow your reaction times, reduce your balance and fine motor skills, and impair your cognition in a way that causes poor judgment, according to the Centers for Disease Control and Prevention (CDC).
Much like caffeine, alcohol is associated with a temporary increase in heart rate and blood pressure. Does that mean drinking the two together could spell extra trouble for your cardiovascular system? Possibly.
When you consume both alcohol and caffeine, the joint impact on your heart might be what you’d expect from the duo: Your heart rate and blood pressure could increase more when you have them both than when you have just one or the other, depending on the amount you consume. But that doesn’t mean mixing caffeine and alcohol results in doubly strong heart effects than consuming one of them alone.
Susan A. Stoner, Ph.D, a research consultant at the Alcohol and Drug Abuse Institute at the University of Washington, tells SELF there does not appear to be a synergistic effect here, meaning there’s no special, mysterious interaction between alcohol and caffeine that exponentially increases the effects of the other. Basically, the effects of drinking alcohol and caffeine together shouldn’t be greater than the sum of the two combined. But if you’re drinking enough alcohol or caffeine to already experience ill effects on your heart, adding the other can just make it worse.
Ultimately, the research on how this combo affects your heart is somewhat mixed and limited, Fritz says. “The lack of knowledge there thus argues for increased caution,” he says. What’s more, “the long-term effects of the combination on cardiac health [are] not known.”
So, the scientific jury is still out on exactly how dangerous it might be for your heart to mix alcohol and caffeine. But when it comes to your brain, experts say that if you put alcohol and caffeine together, the latter effectively “cancels out” some of the former’s effects. This might sound like a good thing, but it can actually be dangerous.
One of the biggest myths out there is that caffeine will help you be more clear-headed and conscientious when you’re drunk. That’s not true.
“A common motive people give for consuming large amounts of caffeine [like] energy drinks along with alcohol is that they are seeking a ‘wide-awake drunk,’” Fritz says. Sure, the caffeine can help combat the sleepiness that often comes with a long night of drinking, but it won’t do anything about the way alcohol affects things like your judgment or motor skills.
“The primary effect of the caffeine and alcohol combination is that the sedative effects of alcohol are reduced,” Fritz says. “Your decision-making and coordination will be just as impaired.” Translation: Since you’re drunk, you’ll still be worse at things like making sound choices and driving in a straight line than you would be while sober. You just might not realize it because the caffeine makes you feel all bright-eyed and on top of your game.
There’s even research out there pointing to an association between this alcohol-caffeine-combo and what experts call “alcohol-related harm.”
It should be noted that all these studies looked specifically at mixing alcohol with energy drinks, as opposed to say, a mixed drink with caffeinated soda or a cup of coffee right before you start drinking. So it’s possible that there are other factors in play here, like energy drink ingredients not present in soda (more on that later). Or maybe people who favor this combination over straight up alcohol or caffeine tend to be more risk-prone people in the first place.
With those caveats in mind, one 2015 review in Drug and Alcohol Dependence analyzing 62 studies found that young adults who drank alcohol with energy drinks experienced more “alcohol-related harm,” like drunk driving and having unprotected sex, than other drinkers.
A different 2015 review in Nutrition Reviews found “compelling evidence” that consuming alcohol and energy drinks is associated with higher rates of binge drinking, engaging in risky sexual behavior, drunk driving, and requiring medical treatment than consuming alcohol alone.
Experts have a few theories why mixing caffeine with alcohol can be more dangerous than alcohol on its own, starting with the simple fact that staying awake for longer probably means you’ll keep drinking longer and you’ll stay out later.
This basically means you could have a longer window of time to get into trouble. That jolt of energy is simply extending waking hours for Drunk You when you might otherwise safely sleep off your intoxication. This increases opportunities for you to run around engaging in risky behaviors and poor decision-making the way people under the influence are wont to do.
It also gives you a chance to drink even more, which increases your risks of drinking too much or even winding up with alcohol poisoning, which can be fatal. As the CDC notes, caffeine’s effect of masking alcohol’s depressant effects can make you feel more alert than you would without the caffeine, possibly prompting you to drink in excess.
OK so we know that combining alcohol with energy drinks and other caffeinated beverages is frowned upon. But what about just having some coffee when you’re drunk to help you sober up? Yeah…that’s not a thing.
There’s no point in chugging caffeinated drinks when you’re drunk. It won’t somehow make the alcohol evaporate from your system.
“Contrary to popular belief, caffeine does not ‘sober you up,’” Stoner says. In order to do that, caffeine would need to expedite how your liver metabolizes alcohol, but it doesn’t have that superpower, Stoner explains. Instead, going overboard on caffeine in an attempt to sober up can actually lead to those previously mentioned ill effects, like shakiness, heightened anxiety, and a racing heartbeat.
There are many important questions yet to be answered when it comes to mixing these two substances, but one thing is clear: This is a combination best worth avoiding.
Experts are still researching whether or not combining alcohol and caffeine bears long-term health implications and how the many other ingredients commonly found in energy drinks other than caffeine (including sugar and herb-based stimulants) could potentially affect your intoxication. And while the fact that the amount and pace at which you consume each substance independently moderates their effects would indicate that knocking back vodka and energy drinks is worse for you than nursing a rum-and-soda, experts have yet to dive into studying how quantity and timing shape the effects you feel. “To my knowledge, this has not been carefully examined,” says Fritz. “It’s an important question.”
Still, there’s enough evidence to show that slamming back caffeinated alcoholic drinks isn’t going to heighten your drunken experience in any meaningful way and can instead increase the risk of experiencing less-than-desirable outcomes—for you and for others. This is about way more than avoiding a hangover. You don’t want to hurt yourself or others because you’re getting intoxicated in a way you don’t realize.
Of course, realistically, you might still decide to mix caffeine and alcohol in pursuit of a perkier buzz. If you do, at least be extremely mindful that, at a certain point, you’re basically playing with liquid fire. Don’t overdo it. “If you do enjoy these types of drinks, pay very close attention to how many drinks you have had,” Fritz says. "As with all types of alcohol, moderation is key.”