It may take 2 to 3 weeks of taking iron supplements before you feel a noticeable difference. Depending on your current iron levels, it may take up to 90 days before you feel an increase in energy. You may need to continue supplementing your dietary iron intake to meet your body's daily iron needs. Iron supplements usually start to take effect after 14 days.
Some may notice improvements more quickly than this. To replenish low iron stores in the body, people must take iron supplements for a minimum of 3 months. Functional iron deficiency (moderately low iron stores in ferritin with normal hemoglobin) can be corrected with oral iron (in pills) when the cause is an insufficient daily intake of iron from the diet. Iron pills, even low-dose pills, will replenish stocks very soon, usually within 3 to 4 weeks.
If functional iron deficiency progresses to anemia, oral iron alone may not be enough to replenish stores. For a while, you can try a combination of oral iron and diets that include lean red meat. Iron deficiency with anemia is a serious health threat and must be monitored at least once a month. The underlying cause, which may be blood loss due to cancer or absorption problems, will determine the best approach to replenishing iron stores and red blood cell levels.