Father-of-2 Tom Mansfield had miscalculated the amount of powder he was meant to use on kitchen scales.
An inquest in Ruthin heard the 29-year-old from Colwyn Bay fell ill straight after drinking his mixture on 5 January 2021.
Reaching a conclusion of misadventure, coroner John Gittins said the cause of death was caffeine toxicity.
Caffeine is used by some gym-goers, with some fitness websites recommending it for improving sports performance in certain doses.
However, experts have warned that when taking powders there is a risk of consuming over the recommended amount.
On Tuesday an inquest heard Mr Mansfield began clutching his chest & complaining his heart was beating fast after consuming the product.
Minutes later, after going to lie down, he began foaming at the mouth. His wife Suzannah alerted neighbors & family & called an ambulance
Paramedics tried to resuscitate him for 45 minutes but was later pronounced dead at Glan Clwyd Hospital in Bodelwyddan, Denbighshire.
The lowest weight measured by Mr Mansfield's scale was more than 6 times the maximum recommended dose
The hearing was told the scales Mr Mansfield had used to measure the powder had a weighing range from 2 to 5,000 grams, whereas he was attempting to weigh a recommended dose of 60-300mg.
It was this miscalculation which led to a massive overdose.
A post-mortem examination showed Mr Mansfield had caffeine levels of 392mg per liter of blood.
Caffeine levels would typically be 2 to 4 milligrams per liter if someone had drunk a cup of filter coffee.
Mr Gittins said it appeared Mr Mansfield had been aiming for the "mid-range of the recommended dose", but "he got his math wrong" & there were "unintended consequences" which had a fatal effect.
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Source: BBC
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