What Happens When You Mix Alcohol and Caffeine? A Doctor Explains

Have you ever wondered what happens in your body when you drink caffeine and alcohol together? Cocktails with this combination aren't a new idea by any stretch. Rum and Coke, Red Bull and vodka, Irish coffee, and many other mixed-drink combinations have been bar staples for years.

There's something special about the espresso martini—typically made with espresso, coffee liqueur, vodka, and often a hint of simple syrup—that feels like a decadent treat. It has all the qualities of a delicious dessert, post-meal pick-me-up, and elegant cocktail that makes it all the more tantalizing.

First concocted by London bartender Dick Bradsell in the '80s, espresso martinis are making a serious comeback. They're on just about every menu these days, and this velvety sip is so good it can make you feel like you're not drinking any alcohol at all: a gift and a curse.

Is this type of cocktail safe to enjoy, or should we avoid mixing caffeine and alcohol altogether? To find out how this combo affects your health, we tapped Seema Bonney, MD, functional medicine doctor and founder of the Anti-Aging and Longevity Center of Philadelphia, to break it down.

Caffeine Content Varies

If you're having trouble staying awake during a night out and want to try some sort of alcohol-and-caffeine drink, Dr. Bonney urges you to consider the amount of caffeine in the beverage. "The higher the caffeine content, the greater the stimulant effect and masking of alcohol effects," she says.

According to a chart published by the Center for Science in the Public Interest, a cup of coffee has between 95 and 165 milligrams of caffeine. The same chart shows that an energy drink typically contains between 40 and 350 milligrams of caffeine, and usually includes added sugars, which is an additional stimulant.

Effects of Mixing Alcohol and Caffeine

In the 2000s, manufacturers introduced caffeinated alcoholic beverages—premixed drinks that combined alcohol, caffeine, and other stimulants—targeting their sales to the youth market. In 2010, the U.S. Food and Drug Administration forced those products off the market, stating they were not "generally recognized as safe," which is their legal standard. Here are some reasons why they're not considered safe.

Caffeine Makes You Feel Less Drunk

Let's start with a cocktail's caffeine component, which Dr. Bonney says is what you need to pay attention to. When you ingest caffeine, it "wards off drowsiness and suppresses adenosine, [a natural chemical in the body that] helps regulate wakefulness and sleepiness, and builds up in your brain throughout the day," she explains.

Alcohol, on the other hand, "causes adenosine to accumulate, making you feel drowsy," Dr. Bonney continues. When both are mixed and ingested, caffeine can mask the depressant effects of alcohol. "This makes drinkers feel more alert and that they can handle more alcohol, creating increased impairment and more risk for harm."

But this doesn't mean that caffeine sobers you up. If you ever turned on a TV, you've probably seen characters suggest a strong cup of coffee for someone who's had too much to drink. "Caffeine has no effect on the metabolism of alcohol by the liver, and thus it does not reduce blood alcohol concentrations or reduce impairment," Dr. Bonney contends, adding the only way to sober up is time.

A Double Hit of Dehydration

Alcohol is a diuretic, meaning consuming it actively removes water from the body. A huge reason you wake up feeling awful after a night of drinking is that your body is dehydrated. "Because caffeine is a mild diuretic, the combination may be even more dehydrating," Dr. Bonney says.

To stave off dehydration, water is your best friend. "If you plan on having a few cocktails, it's best to be well hydrated throughout the day: Drink half your weight in ounces of water daily; [and] consume a glass of water in between each cocktail, and another before you go to bed and as soon as you wake."

It's Heart-Unhealthy

The combination of caffeine and alcohol is potentially dangerous for your heart. "It has already been established that excessive amounts of alcohol can negatively impact heart health, combining alcohol with caffeine could put you more at risk, especially if regularly consumed together," Dr. Bonney explains.

"Caffeine and alcohol both stimulate atrial fibrillation, AKA irregular heartbeat," Dr. Bonny continues. "Both can have a dire effect on the quality and quantity of sleep, which can lead to even more health issues."

Increased Risk of Injury

According to the Centers for Disease Control and Prevention, drinkers who mix alcohol with highly caffeinated energy drinks are more likely (than drinkers who do not mix alcohol with energy drinks) to report unwanted or unprotected sex, driving drunk or riding with an intoxicated driver, or sustaining alcohol-related injuries.

Association with Binge Drinking

A study published by Pub Med found an association between young drinkers of alcohol with energy drinks and binge drinking. Yes, a college student going on a nightly Red Bull-and-vodka bender is a far cry from a mature adult enjoying a once-in-a-blue-moon Energy Long Island iced tea on a hot summer evening. Nevertheless, it's a risk you should be aware of, especially if you're a parent of a young adult.

Bottom Line

Of course, how your body handles the mix of caffeine and alcohol depends on a variety of factors, the most important among them is the amount of caffeine in your drink—which varies widely, especially when it comes to energy drinks. Other factors to consider are your personal health history and how often you drink these combo beverages.

The bottom line is: Enjoy your caffeinated cocktails—but practice moderation. "An occasional, indulgent espresso martini [or other combo beverage] is not likely to cause any harm, we just want to avoid creating a habit of mixing alcohol and caffeine," warns Dr. Bonney.