All the Possible Side Effects of Iron Pills (and How to Take Them Correctly)

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On August 30, 2025

Without sufficient iron, your body cannot produce the number of normal red blood cells needed to keep you healthy. Iron also aids healthy muscle metabolism, neurological development and hormone synthesis, per the National Institutes of Health (NIH).

Your doctor may recommend you take iron supplements if you are deficient or have another underlying health condition, but you should be aware there are side effects of iron pills.

If you find yourself feeling worse after taking an iron supplement, here’s what you need to know.

Iron pills, available as various ferrous ion salts, can be beneficial to treat a deficiency with the proper dosage, but taking too much can result in health risks of toxicity, including acute liver damage.

How Much Iron Should You Take per Day?

Iron is an essential component of hemoglobin, the protein in red blood cells that transfers oxygen from your lungs to every tissue in your body. Iron supports muscle contraction and helps maintain healthy connective tissue. It is also necessary for neurological development, synthesis of hormones and proper growth.

The amount of iron you need on a daily basis depends on your age and sex. The National Institutes of Health lists the recommended dietary allowance necessary to meet your nutritional requirements. The average amount for adults ages 19 and older is between 8 and 18 milligrams.

The tolerable upper limit (UL) for iron is 45 milligrams for people ages 14 and older and 40 milligrams for those younger than 14. Be sure to read the labels before taking any supplements to make certain you’re within the safety range of 45 milligrams of iron for adults, per the Harvard T.H. Chan School of Public Health.

Iron supplements are available in stand-alone forms, including tablets, capsules, powders and liquids, or combined with other vitamins or minerals. Formulations can differ significantly in their iron content.

Foods High in Iron

Even if you’re not iron-deficient, foods high in iron are still an important part of a balanced, healthy diet. Some examples of iron-rich foods you can incorporate include the following, per the USDA:

Ready-to-eat cereals
Hot wheat cereal
Oysters and mussels
Beef
Sardines
Shrimp
Spinach
Soybeans
Swiss chard
Lentils
White beans
Beets
Mushrooms
Black beans
Sweet potato
Cashews
Sesame Seeds

Who Needs to Take Iron Pills?

Despite eating a balanced diet, you may discover your body has depleted its stores of iron. This can result in iron deficiency anemia symptoms, according to the Mayo Clinic, which may include:

Extreme fatigue and weakness
Pale skin
Chest pain, fast heartbeat or shortness of breath
Headache or dizziness
Cold hands and feet
Inflammation or soreness of your tongue
Brittle nails
Cravings for unusual substances, such as dirt or ice
Poor appetite, especially in infants and children

To correct iron deficiency, you may need to take iron supplements. It is important to make sure you take the correct dosage, as too much iron can be dangerous.

Most people get sufficient iron from their diet. However, because iron is primarily found in animal products, people who are on a restricted diet or are vegetarians may have low iron levels. In addition, certain conditions may increase your need for iron, according to Mayo Clinic. Some of these include:

Bleeding problems, such as from peptic ulcer, colon polyps or hiatal hernia
Dysfunctional uterine bleeding
Burns
Kidney dialysis
Intestinal diseases that inhibit absorption. such as celiac disease
Stomach problems or surgical stomach removal
Medications used to increase your red blood cell count

If none of these are to blame for your low iron levels, your doctor may run tests to detect colon cancer, which can bleed and slowly cause iron deficiency even without obvious blood in stools, according to a March-April 2023 review in Cancer Diagnosis & Prognosis.

Excessive iron through supplements (or an accumulation of iron through a combination of food and pills due to a hereditary condition called hemochromatosis) can mess with your organs and result in adverse health complications, like damage to your liver, per the Mayo Clinic.

What Are Signs That Iron Pills Are Working?

You will likely feel less fatigued, less dizzy and less weak after you’ve begun taking iron pills, especially if you have anemia. It can take anywhere from one to four weeks to feel the positive effects of taking iron pills daily (or as prescribed by your doctor), per the Cleveland Clinic.

Find a list of the best iron supplements here.

Side Effects of Iron Pills

Iron pills, if taken correctly, can replenish the iron in your blood to normal after about two months, but the National Library of Medicine (NLM) suggests you continue to take the supplements for another six to 12 months to build up the iron stores in your body’s bone marrow.

If you think you’re feeling worse after taking iron supplements, it’s common to experience some side effects of iron pills — ferrous sulfate, ferrous fumarate and ferrous gluconate forms included. For example, if you’re feeling dizzy after taking iron supplements, it could be due to your lingering deficiency or the pill itself.

According to the NLM, iron supplement side effects include:

Dark urine color
Constipation or diarrhea (rink plenty of fluids and include adequate amounts of fiber in your diet to combat this symptom)
Dizziness
Gastrointestinal discomfort (take iron pills with meals to avoid symptoms of nausea)
Black stools
Liquid forms of iron can stain your teeth (try mixing the iron with a liquid and drinking the solution through a straw to avoid this)
Interactions with certain medications like penicillin or those used to treat seizures or Parkinson’s disease

You shouldn’t be alarmed if your stools are very dark. This is one of the signs iron pills are working correctly. But let your doctor know if:

Stools are tarry-looking
Red streaks are present in your stool
You have cramps, sharp pains or soreness in your stomach

What Is Iron Toxicity?

Taking an extremely higher than recommended amount of iron supplements could result in a severe iron overdose. Accidental poisonings can happen if a child accidentally eats too many pediatric multivitamins or adult prenatal vitamins, warns the NLM. Symptoms of an iron overdose can affect the entire body and include:

Stomach and intestines: liver damage, nausea and vomiting blood, metallic taste in mouth, black bloody stools
Respiratory system: buildup of fluids in the lungs
Heart: low blood pressure, fast and weak heartbeat, shock, dehydration
Nervous system: chills, fever, seizures, headache, drowsiness, apathy, coma
Skin: bluish-colored lips, fingernails and palms of hands; skin flushing, pale skin

Symptoms of iron toxicity may decrease in a few hours, then return again after one or more days.

How to Treat Iron Toxicity

Severe iron toxicity will require you to visit the emergency room to receive immediate and proper care. You will likely receive IV fluids and be monitored to watch for blood pressure and pulse abnormalities, which could indicate the need for more aggressive treatment to remove iron from the body.

Doctors may also give you a medication called deferoxamine, which may need to be administered over the course of 24 hours, per the University of Utah Health.

How to Take Iron Pills Correctly

First and foremost, if you’re prescribed iron pills by your doctor, you should take them as prescribed.

When should you take iron supplements? Try to take them on an empty stomach so they’re better absorbed by your body. Aim to take your iron pills at least one hour before or two hours after eating a meal, per the Cleveland Clinic.

If you’re taking a tablet form of iron, take it whole (do not crush or chew it) for maximum efficacy. If you’re taking a liquid form, make sure you use a measuring syringe or cup, not a spoon, so you can accurately measure the amount you’re getting, per the Cleveland Clinic.

Other tips include avoiding taking iron pills with milk, caffeine, antacids or calcium supplements. You can also take it with orange juice (which contains vitamin C) to help increase iron absorption, per the Cleveland Clinic.

When to See a Doctor

If you believe you have an iron deficiency or anemia, visit your doctor, who can perform a blood test to determine whether you are deficient. From there, your doctor may recommend including more iron-rich foods in your diet, or an iron pill.

If you think you’ve taken too much iron and are feeling the side effects of iron toxicity, call your doctor or nearest emergency room and get treated as soon as possible.

FAQ

1. How Long Does Nausea From Iron Pills Last?

You may feel nausea from taking iron pills right away, or you may feel it over the period of time that you take them. Typically, your body will get used to the iron pills around one to four weeks in, which is when you’ll notice symptom relief, per the Cleveland Clinic.

2. Why Do I Feel Worse After Taking Iron Tablets?

Iron pills are typically taken on an empty stomach, but sometimes, this can cause upset stomach, causing you to feel worse after taking iron supplements. This is why to start out, you may want to take iron pills with a bit of food until your stomach adjusts, per the Cleveland Clinic.

You may also feel worse while taking iron pills if you experience any of the side effects mentioned above. And if you’re iron-deficient, it may take a while for the iron pills to begin working and relieving your symptoms. All are reasons you could feel worse for a while; but talk to your doctor if your symptoms don’t improve.

3. What Are the Stages of Iron Deficiency?

Iron deficiency anemia develops over three stages. During the first stage, iron stores are depleted, but it hasn’t yet affected your red blood cells.

In the second stage, the normal process of making red blood cells is altered — causing a condition called iron-deficient erythropoiesis (where bone marrow is made without enough hemoglobin), per the Cleveland Clinic.

By the third stage, you have full-on iron deficiency anemia, i.e., there isn’t enough iron to make hemoglobin. This is when you begin to experience symptoms, per the Cleveland Clinic.