Pure Lab Vitamins Carbonyl Iron- An ideal source of essentially pure iron with low toxicity, minimal metallic taste, no gastro-intestinal pain nor constipation and excellent bioavailability. The high iron content and high absorption rate results in lower dose per capsules, achieving the same or better daily intake levels, compared to ferrous salts, while at the same time and most importantly, side effects like constipation and gastro-intestinal discomfort and pain are avoided. In addition to the high iron content, a key physical property of Carbonyl Iron is its fine spherical particle size and porosity with huge surface area, both resulting in higher human bioavailability than other iron form. Carbonyl Iron helps to restore and increase ferritin levels quickly so you can perform at your best.