This is an important study as it finds stimulants in pre workout type supplements – currently all the rage in the marketplace – can range significantly over time for the same product, up to 266%! When you combine various stimulants – many of which are listed in the abstract below – it can be potentially dangerous. Manufacturers of such products need to do a far better job of their quality control. Before anyone comments the FDA needs to regulate supplements, I’d recommend reading my article HERE on the total failure of FDA “regulated” drugs and the massive (yet never mentioned in the media…) quality control failures of pharma.

Although the authors of this study admit their sample size was insufficient to support statistical analysis, I commend them for examining “Three samples of nine popular sports supplements were purchased over the nine-month period” vs just pulling a single sample off the shelves of some store and making the conclusions they did. I think their sample size and methodology sound enough that people should take note that it’s very likely the stimulant levels in the pre workout supplements they use may be all over the place dose wise. Many ingredients found in nutritional supplements are non toxic at levels well above label claims, especially acutely, but stimulants, especially mixtures of various stimulants, can be problematic. Per usual, buyer beware!

Some popular pre workout formulas

Some popular pre workout formulas

Variability of Stimulant Levels in Nine Sports Supplements Over a Nine-Month Period.

Int J Sport Nutr Exerc Metab. 2016 Feb 3.


Many studies have found that some dietary supplement product labels do not accurately reflect the actual ingredients. However, studies have not been performed to determine if ingredients in the same dietary supplement product vary over time. The objective of this study was to assess the consistency of stimulant ingredients in popular sports supplements sold in the United States over a nine-month period.

Three samples of nine popular sports supplements were purchased over the nine-month period. The 27 samples were analyzed for caffeine and several other stimulants (including adulterants). The identity and quantity of stimulants were compared to stimulants listed on the label and stimulants found at earlier time points to determine the variability in individual products over the nine-month period.

The primary outcome measure was the variability of stimulant amounts in the products examined. Many supplements did not contain the same number and quantity of stimulants at all time points over the nine-month period. Caffeine content varied widely in five of the six caffeinated supplements compared to the initial measurement (-7% to +266%).

In addition, the stimulants – synephrine, octopamine, cathine, ephedrine, pseudoephedrine, strychnine, and methylephedrine – occurred in variable amounts in eight of the nine products. The significance of these findings is uncertain: the sample size was insufficient to support statistical analysis. In our sample of nine popular sports supplements, the presence and quantity of stimulants varied over a nine-month period.

However, future studies are warranted to determine if the variability found is significant and generalizable to other supplements.



Will Brink is the owner of the Brinkzone Blog. Will has over 15 years experience as a respected author, columnist and consultant, to the supplement, fitness, bodybuilding, and weight loss industry and has been extensively published. Will graduated from Harvard University with a concentration in the natural sciences, and is a consultant to major supplement, dairy, and pharmaceutical companies.


His often ground breaking articles can be found in publications such as Lets Live, Muscle Media 2000, MuscleMag International, The Life Extension Magazine, Muscle n Fitness, Inside Karate, Exercise For Men Only, Body International, Power, Oxygen, Penthouse, Women’s World and The Townsend Letter For Doctors.


Will is the author of the popular e-books, both accompanied by private members forum access , Bodybuilding Revealed & Fat Loss Revealed.


You can also buy Will's other books on Amazon, Apple iBook,  and Barnes and Noble.

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