Energy Drinks: Are They Zapping More Than Your Thirst?

Welcome to “Ask the Expert,” a UTHealth Houston news series where our leading experts examine pressing health challenges. In this edition, we address energy drinks.

Written by John Higgins, MD, MBA, MPHIL, professor and cardiologist at McGovern Medical School at UTHealth Houston

John Higgins, MD, MBA, MPHIL, professor and cardiologist at McGovern Medical School at UTHealth Houston. Credit: UTHealth Houston

Let’s get one thing straight: That canned drink can promise “explosive energy,” but it isn’t bottled magic. It’s mostly caffeine, sugar, and a chemistry set of extras, all working together to make your heart beat like it’s late for a meeting. It’s not bottled vitality—it’s a stimulant delivery system.

How the buzz actually works

Caffeine blocks the brain chemical that tells you, “Hey, maybe rest now.” Block that signal, and suddenly you feel alert—but your heart rate climbs, blood vessels tighten, and blood pressure ticks up, too. It hits fast (30-120 minutes) and can linger for hours, depending on your body, genes, and how much caffeine you’re already used to.

Then there’s the sugar—sometimes 50 or more grams per can, or basically a candy bar you drink. That’s the “boost,” and later, the inevitable “crash.”

One myth to kill: Energy drinks are not the same as sports drinks. Sports drinks replace fluids and electrolytes. Energy drinks just rev your engine and are badly suited for actual hydration.

What’s really in the can?

Beyond caffeine, you’ll find taurine, guarana, ginseng, B vitamins, and other ingredients with fancy names that sound healthy but aren’t fully understood in combination. A few standouts:

•   Guarana and yerba mate: A sneaky extra caffeine source not always obvious from the label.
•   Taurine: An amino acid that has complicated effects when mixed with caffeine.
•   Yohimbine and similar stimulants: Can crank up anxiety, blood pressure, and heart rhythm issues.
•   “Proprietary blends”: A fancy way of saying, “Trust us.” This can appear on the ingredients list as a grouped list of active components such as caffeine, taurine, and ginseng, where companies disclose the total weight of the mixture rather than the precise amount of each individual ingredient.
•   Megadose B vitamins: Energy drinks often contain thousands more percent of your daily needs, which won’t actually create more energy if you weren’t deficient to begin with.

What science says about your heart

This isn’t just hype—researchers have measured real effects. They have found that energy drinks bump systolic blood pressure by about 4.4 mmHg on average, and more with high-caffeine drinks. In one trial, an energy drink caused more electrical changes in the heart than caffeine alone, meaning the whole mix of ingredients matters, not just the caffeine.

In my research, we found that after a large energy drink, blood vessels’ ability to relax and expand dropped by nearly half within 90 minutes, even in healthy young adults. Also, one 24-ounce can of an energy drink was enough to cut peak flow-mediated dilation (a gold-standard measure of how well an artery relaxes) from 5.9% down to 1.9% in just 90 minutes, even though heart rate and blood pressure barely budged. In other words, your blood vessels can take a hit before your vitals even seem to notice.

Although most people won’t have a dramatic reaction, there are documented cases of irregular heart rhythms, chest pain, and even cardiac arrest tied to heavy or fast consumption, especially in people with underlying heart issues.

The everyday side effects

More common than a trip to the ER are jitters, headaches, insomnia, nausea, and the sensation of your heart doing a drum solo. In one survey, over half of young energy drink users reported at least one bad reaction, worse odds than plain coffee.

So, how many is too many?

There’s no magic number since cans range from 80 mg to 400 mg or more of caffeine. But I recommend kids and teens skip them entirely, as their bodies aren’t adapted to high amounts of caffeine. For healthy adults, one can at a time will do the trick, but adults should avoid making it a daily habit.

Keep daily totals of caffeine, including coffee, soda, tea, and supplements, under 400 mg. Do not stack coffee, preworkout, an energy drink, or diet pills in a day. Never mix with alcohol—it won’t sober you up, but instead make you a wide-awake, bad decision-maker. Never use energy drinks as a hydration tool. Some people should avoid them completely, including those who are pregnant or breastfeeding and anyone with heart conditions, high blood pressure, or caffeine sensitivity.

Red flags to stop and call a doctor

Too much caffeine consumption can be deadly. If you experience chest pain, fainting, a racing or irregular heartbeat, severe shortness of breath, confusion, or seizures, stop drinking and get help immediately.

Bottom line

The best source of sustainable energy isn’t found in a can. It comes from sleep, hydration, food, and exercise. Energy drinks might mask fatigue for a bit, but they won’t actually fix it. Your body’s not asking to fly. It’s asking for a power nap.

John Higgins, MD, MBA, MPHIL, is a professor of medicine and sports cardiology with McGovern Medical School at UTHealth Houston. All quotes should be attributed to him.

Energy drinks: Are they zapping more than your thirst? originally appeared in UTHealth Houston News.