Protein CX and Natural Energy Max are not sold at GNC, but other protein supplements and energy products are available there. Protein CX should not be confused with protein Cx43, which is involved in the behavior of human prostate cancer cells, according to the National Institutes of Health.
GNC sells protein in whey, cassein, soy, egg and other blends. Protein products are packaged as bars, liquids and meal replacements as well as protein for weight gain. Energy supplements are available as drinks, powder, gel, chewables, and "shots" advertised as cures for a hangover. GNC also sells energy supplements in long-lasting and extra-strength compounds, according to the company's website.