From a 2004 IOC-lab study finding undeclared prohormones in about 15 percent of samples to modern stimulant adulteration, contamination is documented, category-specific and manageable.
Recent pooled analyses put beta-alanine's benefit near 2.85 percent — concentrated in efforts lasting about one to ten minutes.
US rules require a proprietary blend to list its ingredients by weight order and its total weight — but not a single individual amount.
Independent tests of protein powders have detected cadmium, lead, arsenic and mercury at varying levels — mostly trace, occasionally elevated, and never zero.