For many with hair loss, low iron levels has nothing really to do with their hair loss. Ferritin levels come up and hair density does not change. However, if you are in fact an individual in who iron is a causative factor in your hair loss, it will take 3-6 months for an improvement. As a hair specialist, I would love it if iron had more of a role for my patients, but far too much emphasis is placed on iron levels in hair loss which ultimately leads to disappointment for many when hair does not improve after appropriate supplementation. REFERENCE Sinclair R. There is no clear association between low serum ferritin and chronic diffuse telogen hair loss. Br J Dermatol. 2002 Nov;147(5):982-