How Long Does It Take Iron Supplements to Work?

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On September 1, 2025

Iron supplements, usually ferrous sulfate, ferrous fumarate or ferrous gluconate, will start to take effect within a few weeks after you start taking them. However, the length of time it takes for your body to completely replenish your depleted iron stores will depend on how severe your anemia is to begin with, how long you’ve been anemic, how well your body is able to absorb the iron in the supplements and how good you are at remembering to take them according to your doctor’s instructions.

If you’re anemic, your symptoms should begin to improve within two to three weeks of starting iron supplementation. However, it may take up to six months to cure your anemia.

Iron-Deficiency Anemia

When you’re anemic due to iron deficiency, your body isn’t making enough hemoglobin to carry oxygen to all of your cells. Hemoglobin is a protein that carries oxygen in your red blood cells. Your bone marrow produces red blood cells using iron, vitamin B12, and other vital minerals and enzymes.

Iron Supplements for Anemia Treatment

The American Society of Hematology says that the most common cause of anemia is iron deficiency. Although most people in the U.S. get enough iron in their diets, some people have difficulty absorbing the mineral, and others are losing blood faster than their bodies can replace their red blood cells. This may make iron supplements the ideal treatment.

Iron is a raw material that your body needs to make new red blood cells. If your doctor has determined that you’re anemic, she will probably do a blood test to be sure that it’s an iron deficiency and not another issue that’s causing the problem.

Read more: Iron Deficiency That Is Not Anemia

Most likely, she will require changes in your diet or she’ll prescribe iron supplements and give you specific instructions about when to take them. Once the iron from the supplements starts to get into your system, your bone marrow will kick into action, turning out new red blood cells.

Duration of Iron Supplementation

Continue taking your iron supplements for as long as your doctor advises. She will continue to test your blood while you’re recovering from anemia to check the amount of hemoglobin in your blood. She may also use a microscope to look at the shape and color of your red blood cells.

As suggested by an Intermountain Healthcare article, it usually takes two to three weeks before symptoms of anemia improve. There aren’t any particular signs iron pills are working, but you should have more energy throughout the day. In some cases, it may take up to six months of consistent supplementation to cure anemia. If your iron levels are very low to begin with, your doctor might elect to use intravenous supplementation.

Complications From Excessive Iron

Even though you may be taking large amounts of iron every day, your body won’t be able to absorb all of it. If you take high doses of supplemental iron — 45 milligrams or more per day — you may be at risk for iron overload and experience symptoms like constipation or nausea, notes the National Institutes of Health.

The National Institute of Diabetes and Digestive and Kidney Diseases indicates that hemochromatosis is a disease caused by iron overload. One form of the disease is genetic, and the other is caused by excess hemoglobin levels that can happen after a blood transfusion. This disease can cause joint pain and fatigue or complications like diabetes and abnormal heartbeat.

Avoiding Common Mistakes

Taking antacids or drinking milk with your pills can decrease the amount of iron you actually absorb. It’s best to take the supplements on an empty stomach, but this might make you queasy. You can take iron supplements with food, but you should avoid high-fiber foods or foods and beverages containing caffeine, according to a 2018 Medline Plus article. If you frequently miss doses or stop taking the supplements, you will obviously have slower results.

Read more: Foods to Eat If You Have Low Iron