From caffeine to creatine, what pre-workout powders do to your body

Some people won’t brave the gym until they’re caffeinated, while others might quickly scarf down a banana.

Many gym-goers have a pre-workout ritual centred around food and drink; some more complicated (and expensive) than others.

If you’ve vowed to hit the gym in 2025, you may well encounter “pre-workouts”: powders containing a range of supplements promising benefits such as bulked-up muscles and increased endurance.

So what exactly do these brightly coloured (and sometimes pricey) products contain, and is there evidence to support you taking them?

Caffeine: a well-known performance enhancer

The most common ingredients in pre-workouts are the two Cs: caffeine and creatine.

Andre Nelson, who researches sports nutrition at Victoria University, says the evidence base for caffeine is strong.

“It has what we’d term small-to-moderate-sized benefits on performance.”

In fact, caffeine is such a well-known “performance enhancer” that it was on the International Olympic Committee’s banned substance list until 2004.

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Caffeine works by releasing adrenaline into the bloodstream, as well as neurotransmitters in the brain, including noradrenaline and dopamine.

“That has broad effects, including reducing perceptions of pain and exertion, and delaying fatigue,” Dr Nelson says.

He advises consuming around two milligrams of caffeine per kilogram of body weight.

For a 100kg person, then, that’s 200mg of caffeine (or around two cups of coffee).

On the other hand, Dr Nelson says too much caffeine can lead to unwanted side-effects such as “edginess, nervousness and over-stimulation”.

Timing when you take caffeine is important, too.

Dr Nelson suggests consuming it around one hour before your workout for its beneficial effects to “peak” at the right time.

Taking it too late, on the other hand, can be problematic.

“We know that caffeine consumption can impact sleep, so you probably want to be taking it [at latest] about nine hours before your bedtime,” Dr Nelson says.

“If you’re an afternoon or evening exerciser, I wouldn’t recommend consuming anything with caffeine in it.”

Are there benefits to creatine?

Creatine is the second-most popular ingredient in pre-workouts, owing to a large body of research that shows it may be beneficial for strength training in particular.

When our muscles contract, they use a source of energy called ATP or adenosine triphosphate.

Our body only stores a small amount of ATP in our muscles, and these reserves can deplete quickly.

Creatine helps replenish those stores, making it ideal for short-duration, high-intensity work.

But there is a caveat, according to Mandy Hagstrom, an exercise scientist at the University of New South Wales.

Not everyone seems to respond to creatine in the same way, and it isn’t effective without exercise.

“My mum asked the other day if she should start taking creatine, and I was like, ‘Mum, you need to go to the gym first,'” she laughs.

But the good news is that creatine, which is found in red meat and seafood, is safe to take as a supplement long term with minimal side effects.

Dr Hagstrom says some people might get an “upset tummy” at high doses, while others report bloating and fluid retention when first introducing it to their diet.

As an added bonus, Dr Hagstrom says evidence is emerging that suggests creatine is beneficial for cognitive health, and may even help recovery from concussion.

What about the rest of the ingredients?

So far, it may seem like the evidence is good for pre-workouts, especially if they contain caffeine and creatine.

But both Dr Nelson and Dr Hagstrom warn that there are several reasons to avoid them.

The first is that supplements are poorly regulated in Australia.

Dr Hagstrom says up to one in four supplements is either contaminated or does not contain ingredients consistent with what is listed on the label.

Some supplements have even been found to contain heavy metals that have been linked with cancer and dementia when consumed in large amounts over long periods of time.

“You just don’t know what you’re putting in your body,” she says.

“When you pick up these pre-workout mixes, the ingredient list is so long, and full of so many things you probably haven’t heard of.

“My rule is if I don’t really know what something is, I really don’t want it in my body.”

Dr Nelson adds that other common pre-workout ingredients, such as amino acids, have little evidence to support their consumption.

Amino acids are the “building blocks” of proteins. Our body makes hundreds of them, but has to source nine of them (called “essential” amino acids) from food.

“[Amino acid supplements] are basically a waste of money,” Dr Nelson says.

“If you’ve got a diet that contains sufficient protein, you’ll be getting more than enough of those amino acids.”

One of the amino acids commonly used in pre-workouts, beta alanine, can also cause the unpleasant side effect of pins and needles.

Dr Hagstrom says these are all reasons to look to food, not supplements, to meet nutritional needs and enhance performance.

She advises getting enough protein — just under 1g per kg of body weight per day — and consuming carbohydrates before working out.

“If you’ve got a long, gruelling exercise session, or you’re going to go for a long run, then carbohydrates will fuel you,” she says.

When you eat your carbs is up to you. As Dr Hagstrom puts it, some people can “run out the door while eating”, while others will need more time to digest.

Once you’ve finished your workout, she advises having a “mixed meal”, which means a combination of protein, fats and carbohydrates.

“Protein is important for muscle repair and growth, and carbohydrates are important to replenish glycogen [a key source of energy] and enhance recovery faster,” she says.

Discover more about pre-workout supplements on What’s that Rash? and subscribe to the podcast to hear Norman Swan and Tegan Taylor unpack more health questions.