Energy drinks: is it the taurine, the sugar, or just expensive caffeine?

The side of an energy drink can reads like a formulation. Taurine. Glucuronolactone. B vitamins. Guarana. Ginseng. The implication is that these ingredients work together, and that the result is something more sophisticated than a cup of coffee with bubbles.

Taurine in particular has had a strange few years. In 2023 it was the molecule that might slow ageing. In 2025 it was the molecule that might feed leukaemia. Meanwhile the cans kept selling, mostly to people at desks who wanted to stay sharp through the afternoon.

So what is actually doing the work in the can? Researchers have run the experiment that answers this, by taking the drink apart and testing the pieces separately.

Taking the can apart

In 2012 a team at Tufts University ran what may be the most useful energy drink study ever done. They gave 48 habitual caffeine consumers, all 24 hours caffeine deprived, four different treatments on four separate days: caffeine alone (200 mg), taurine alone (2000 mg), both together, or neither. On top of that, half got 50 g of glucose and half got a placebo. It was randomised and double-blind. Then everyone did attention, working memory and reaction time tasks.

The caffeine did what caffeine does: it enhanced executive control and working memory, and reduced simple and choice reaction time. It also reduced feelings of fatigue.

Taurine was a mixed bag that averaged out to not much. Taurine increased choice reaction time, meaning it made people slower on that task, but reduced reaction time in the working memory tasks. More strikingly, taurine reversed the effects of caffeine on vigor. People felt less of a lift with it than without it.

Glucose alone slowed choice reaction time.

The authors’ conclusion is unambiguous: caffeine, not taurine or glucose, is likely responsible for reported changes in cognitive performance following consumption of energy drinks, especially in caffeine-withdrawn habitual caffeine consumers.

That last phrase is worth a second look. The participants had gone a day without caffeine. Part of what the caffeine “improved” was the deficit created by missing it. For a daily energy drink user, some of the boost is simply the removal of withdrawal.

An earlier review of the literature reached the same place: most of the effects of energy drinks on cognitive performance are related mainly to the presence of caffeine.

The taurine whiplash

Taurine is an amino acid your body makes on its own, found naturally in meat and fish, and added to most energy drinks.

The longevity excitement came from a 2023 paper reporting that taurine supplementation extended healthy lifespan in worms and mice, by about 12% in the animals. Headlines followed, and so did supplement sales.

Two years later the US National Institutes of Health checked the premise that taurine falls with age. It did not hold. In blood samples from humans, monkeys and mice, taurine levels often increased or remained constant with age, and the researchers concluded there is not yet solid clinical evidence that taurine supplements benefit humans.

Then came the scare. A University of Rochester team reported in Nature that leukaemia cells take up taurine from the surrounding bone marrow and use it to grow faster. When the researchers blocked taurine access in mouse models, cancer growth was suppressed.

That study has been widely misread. It showed that leukaemia cells that already exist use taurine made inside the bone marrow. It did not show that drinking taurine causes leukaemia in healthy people, and it did not test energy drinks. It is a finding about cancer biology that may matter for patients with leukaemia. For everyone else it changes nothing yet.

So the honest summary of taurine is: not demonstrated to slow ageing in humans, not demonstrated to cause cancer in humans, and not demonstrated to improve your thinking.

What a litre does to your heart

If the extra ingredients do not help cognition, do they do anything at all? One well-designed trial suggests they might, and not in a good way.

Researchers at the University of the Pacific ran a randomised, double-blind, placebo-controlled crossover study of 34 healthy volunteers aged 18 to 40 years. On different days, each drank 32 ounces (about 950 ml) of one of two commercial energy drinks or a placebo within an hour, and was monitored for four hours.

Both drinks lengthened the QT interval, a measure of how long the heart’s ventricles take to reset between beats, by 6 to 7.7 milliseconds more than placebo at four hours. There was also a statistically significant 4 to 5 mm Hg increase in systolic and diastolic blood pressure.

Here is the curious part. Each 32 ounce serving contained 304 to 320 mg of caffeine, and caffeine at doses under 400 mg is not expected to produce those ECG changes. The lead author said the changes cannot be attributed to caffeine, and called for work on which ingredient, or which combination, is responsible.

Context matters. The QT changes were small in these healthy young adults. Thirty-two ounces in an hour is two large cans back to back, which is more than most people drink. The participants were young and healthy, and nothing bad happened to any of them. But if the QT interval is too long it can cause the heart to beat abnormally, which is why the finding matters for people with heart conditions or on medication that also lengthens QT. The study itself notes that the impact of long-term energy drinks consumption remains unknown.

What is not known

Which ingredient affects the heart. The trial tested whole drinks. Nobody has yet taken the can apart for cardiac effects the way the Tufts team did for cognition.

What years of daily use does. The controlled studies last hours. There is no long-term trial of habitual energy drink consumption on any health outcome.

Whether sugar-free versions differ. The heart study did not separate sugar from the other ingredients.

Whether taurine at energy drink doses does anything in humans, good or bad, over the long run.

What this means at your desk

You are paying for caffeine. The evidence says the other ingredients contribute little or nothing to alertness, so a coffee or a tea delivers the active ingredient for less.

If you like the taste and drink one can, there is nothing in the trial literature to worry a healthy adult. Treat it as the caffeinated soft drink it is, and count it towards your daily caffeine.

The pattern to avoid is volume and speed: several large cans in a short window. That is the dose at which blood pressure and heart rhythm measurably shift.

If you have a heart condition, high blood pressure, or take medication that affects heart rhythm, that finding is a reason to choose coffee or tea instead.

This is not individual medical advice. Caffeine and energy drinks interact with several medications and conditions, and decisions about them belong with a clinician.

Common questions

Does taurine in energy drinks do anything?

Not much for cognition. In a randomised double-blind trial, caffeine improved attention, working memory and reaction time, while taurine had mixed effects and reversed caffeine’s effect on vigour. The authors concluded that caffeine, not taurine or glucose, is likely responsible for energy drinks’ cognitive effects.

Are energy drinks bad for your heart?

In a trial of 34 healthy adults, drinking 32 ounces within an hour lengthened the QT interval by 6 to 7.7 milliseconds versus placebo and raised blood pressure by 4 to 5 mm Hg. The changes were small, and the long-term impact is unknown.

Does taurine cause cancer?

That has not been shown. A 2025 Nature study found leukaemia cells use taurine from the bone marrow to grow, and blocking it slowed cancer in mice. It did not test energy drinks or show that taurine intake causes leukaemia in healthy people.

Is an energy drink better than coffee for focus?

There is no evidence that it is. Ingredient-by-ingredient testing attributes the cognitive effects to caffeine, which coffee supplies without the added ingredients whose cardiac effects are still unexplained.

The bottom line

Take an energy drink apart and the part that works is the caffeine. Taurine neither sharpens your thinking nor, on current evidence, extends or shortens your life. The one signal worth respecting is cardiac: a litre in an hour shifts heart rhythm and blood pressure in ways caffeine alone should not. One can is a soft drink with a marketing budget. Several in a row is the experiment nobody should run on themselves.