Doctors are being warned about a dangerous pre-workout trend called dry scooping that some gym-goers are doing.
It involves eating protein-rich powder supplements neat, rather than diluting them in water, as recommended by manufacturers, to make a drink, reports the BBC.
Researchers, who are giving a talk at a US medical conference, are worried young teens may try it, spurred on by a flurry of internet videos of the fad.
They scanned TikTok, counting the millions of likes.
Pre-workout powders typically contain lots of amino acids, vitamins and other ingredients, such as caffeine.
The idea is to give the body a boost before a workout to help stamina, although the science around it is patchy.
But there are known risks from taking on too many energy-boosting stimulants.
A big dose of caffeine, for example, can cause heart-related side effects, including palpitations and extra or missed beats.
A scoop of powder might pack as much caffeine as five cups of coffee, say the researchers from the Cohen Children's Medical Center in New York.
This jolt can cause "an increase in blood pressure and heart rate, potentially leading to disturbances in heart rhythm".
And accidentally inhaling the powder into the lungs could cause choking or an infection or pneumonia, say the researchers.
In the UK, the products are regulated as foods rather than medicines, but must be deemed safe for consumption to be able to be sold in shops to people 18 and over.
Some powders sold online may not be from reputable suppliers or contain the ingredients listed on the pack.
Several have since been banned for containing substances such as a synthetic amphetamine called DMAA and a stimulant called synephrine.