This is what is posted under the faq part of the site for the question "what is in it?" :

"It contains all the necessary minerals to grow bigger racks and the best milk for fawns. Specifically, it contains Salt, Calcium, Phosphorous and several Trace Minerals.
Studies have found 11 different minerals in deer antlers. Calcium and Phosphorous being the most dominate. Magnesium and Sulfate are next and then Iron, Potassium, Barium, Zinc, Aluminum and Barium. No one has figured out the significance of these in antler growth other than Calcium and Phosphorous. But deeRoids contains all of them and in the right proportions for maximum growth. "

According to the story on the site they started with salt, then took away as much salt as possible to keep them coming back but still be able to fill it with everything they need.
I personally just saw it on ebay and desided to try it. The molasses flavored has been hit far more then a deer cocain site in my personal field test.