Iron is an essential mineral that plays central roles in energy production, immune system function, and neurological health.* Iron is an essential component of hemoglobin, a molecule that transports oxygen to the cells of the body, and myoglobin, which binds oxygen used in muscle tissues.* NOW uses Ferrochel® Iron Bisglycinate, which has clinically demonstrated superior absorption and is well tolerated because it is gentle and non-constipating.* Ferrochel® is a registered trademark of Albion Laboratories, Inc. NOW® Double Strength Iron has twice the Iron (36 mg per capsule) as in our regular strength product (18 mg per capsule). Natural color variations may occur in this product.