Ted B said:Firms that manufacture steroids, EPO, and/or other products that are subjected to pharmaceutical standards are not typically in the food supplement business.
Supplement companies are 'blenders' that buy, mix, and repackage, and are regulated as food items. Whether they got the proportions correct is the largest potential source of error.
When in doubt, mix your own.
I went into GNC to buy some supplements back in the day. When I realized that the guy selling me this was much less informed than I, I had second thoughts. "This is what you need.... but if you take that, you'll need these to keep your hands from shaking... and if you get those you'll need these to keep you regular."
Very scary that the guy telling me "what I need" may not even have a high school degree... let alone pharmaceutical degree.