Carbonyl® Iron is an ideal source of essentially pure iron with low toxicity, minimal metallic taste, no gastro-intestinal pain nor constipation and excellent bioavailability of 69%. Carbonyl® Iron Capsules is metallic iron (Fe) with high (> 98%) iron content. It is not a salt. It absorbs at 69%, compared to only 10 to 15% with most other forms of iron.