Iron Drug, Supplement and Food Interactions

1. Interaction summary

Iron is one of the most interaction-prone minerals. The reason is simple chemistry: iron binds to other molecules, and its absorption depends on stomach acid and on what else is in the gut at the same time. Most iron interactions are therefore absorption interactions. Iron can reduce how much of a medicine or another mineral enters the blood, and many foods, drugs and supplements can reduce how much iron is absorbed.

This page is a conservative reference. It describes interactions that are documented in clinical studies or in official drug labels, separates them from interactions that are only theoretical, and states how strong the evidence is. It does not tell any individual person how to take their medicines. Timing and dosing decisions belong to the prescriber or pharmacist.

Summary of the main points:

•      Medicines with documented absorption interactions include levothyroxine, fluoroquinolone and tetracycline antibiotics, levodopa, methyldopa, penicillamine, trientine and some HIV integrase inhibitors.

•      Acid-reducing medicines such as proton pump inhibitors can lower iron absorption, mainly over the long term.

•      Calcium, tea, coffee, dairy, whole grains and soy reduce absorption of non-heme iron, while vitamin C and meat improve it.

•      Supplements such as calcium, zinc, magnesium and some polyphenol products may compete with iron.

•      Timing is the most common management strategy, and the right interval depends on the specific product label.

•      Iron overload conditions make some interactions, such as with vitamin C and alcohol, a safety concern.

Medical disclaimer: This page is educational and is not medical advice. Do not start, stop or change any medicine because of it. Speak with a pharmacist or physician about your own medicines.

2. How interactions are identified

Not all interactions have the same level of proof, so it helps to know how they are found. The strongest evidence comes from controlled pharmacokinetic studies, in which volunteers or patients take a drug with and without iron and researchers measure drug levels in the blood. The classic iron and levothyroxine, levodopa and methyldopa studies are of this type.

The next level is clinical outcome evidence, such as a rise in thyroid-stimulating hormone in patients who start taking iron with levothyroxine, or cohort studies linking long-term acid suppression to iron deficiency. These show real effects, but they can be affected by other factors.

Case reports are a weaker source. They are useful for flagging possible problems, but one case cannot prove cause and effect. Drug labels summarize manufacturer data and regulatory review, and they often give practical spacing advice. Interaction databases combine these sources, and they sometimes rate a theoretical risk as seriously as a proven one.

Finally, many interactions are predicted from mechanism. Iron binds, or chelates, certain chemical groups, so any drug with such a group might be affected. A mechanistic prediction is a reason for caution, not proof of harm, and this page labels it accordingly.

Because iron absorption varies with a person's iron status, stomach acidity, meal content and dose, results in one study may not match another. Many of the studies use ferrous sulfate, so findings may not apply equally to every iron form.

3. Drug classes of concern

Medicines fall into three groups. The first group has its own absorption reduced by iron, because the drug binds to iron in the gut. The second group reduces iron absorption, usually by lowering stomach acid. The third group shares side effects with iron, mainly irritation of the digestive tract.

•      Thyroid hormone: Levothyroxine absorption can be reduced when iron is taken at the same time.

•      Antibiotics: Fluoroquinolones such as ciprofloxacin and levofloxacin, and tetracyclines such as doxycycline and minocycline, bind iron and may be less effective if taken together.

•      Parkinson's disease medicines: Levodopa with carbidopa absorption is reduced by iron.

•      Blood pressure medicine: Methyldopa absorption is reduced by iron.

•      Chelating medicines: Penicillamine and trientine bind metals and are affected by iron, and iron chelators such as deferasirox oppose the purpose of iron altogether.

•      HIV integrase inhibitors: Dolutegravir, bictegravir and raltegravir are affected by iron and other polyvalent cations, and labels give specific timing advice.

•      Acid-reducing medicines: Proton pump inhibitors, H2 blockers and antacids can lower iron absorption.

•      Bone medicines: Oral bisphosphonates such as alendronate must be taken on an empty stomach before other substances, which includes iron.

•      Gut-irritating medicines: Nonsteroidal anti-inflammatory drugs and aspirin can add to stomach irritation caused by iron.

Spacing is the usual way to manage these interactions. The idea is to give the other medicine at a different time from iron so that the two do not meet in the gut. Spacing works best for chelation, which happens in the gut, and works less well for effects of acid suppression, which last all day.

4. Specific documented interactions

The table below lists interactions with human data or labeling. "Commonly advised" refers to typical label or reference guidance, which varies by product, so the individual drug label always takes priority.

Drug or class	Documented effect	Strength of evidence	Commonly advised approach
Levothyroxine	Lower thyroid hormone absorption; higher TSH reported	Strong (clinical study, labeling)	Separate by several hours per label
Ciprofloxacin and other fluoroquinolones	Chelation lowers antibiotic absorption	Strong (labeling)	Take antibiotic well before or after iron, per label
Tetracyclines (doxycycline, minocycline)	Chelation lowers antibiotic absorption	Strong (labeling, studies)	Separate by several hours, per label
Levodopa with carbidopa	Lower levodopa absorption; some worse symptom control	Moderate (small clinical study)	Prescriber guidance; separate dosing
Methyldopa	Lower methyldopa absorption and blood pressure control	Moderate (small study)	Prescriber guidance; separate dosing
Penicillamine, trientine	Chelation lowers drug absorption	Moderate (labeling)	Separate dosing, per label
Dolutegravir, bictegravir, raltegravir	Lower integrase inhibitor levels with iron	Strong (labeling)	Specific timing or taking with food, per label
Proton pump inhibitors, H2 blockers, antacids	Lower iron absorption; higher deficiency risk long term	Moderate (studies, cohort)	Clinician review if iron deficiency develops
Oral bisphosphonates	Iron and other substances interfere with absorption	Moderate (labeling)	Take bisphosphonate first on an empty stomach, per label
Mycophenolate	Possible lower drug absorption; data conflict	Weak to moderate	Transplant team guidance

 

Levothyroxine is the best known example. In a study of patients with hypothyroidism, taking ferrous sulfate with thyroxine raised thyroid-stimulating hormone, which indicates reduced thyroid hormone effect. Iron appears to bind levothyroxine in the gut. Levothyroxine labeling advises separating it from iron by several hours.

Fluoroquinolones and tetracyclines form complexes with iron, and the resulting drug levels can fall enough to risk treatment failure. For ciprofloxacin, labeling advises taking it at least two hours before or six hours after products containing iron or other multivalent cations. Other antibiotics have different advice.

Levodopa absorption was reduced when patients took it with ferrous sulfate in a study of people with Parkinson's disease, and some patients showed worse symptom control. Iron may bind levodopa or its partner drug carbidopa.

HIV integrase inhibitors are a good example of how labels handle chelation. Dolutegravir labeling advises taking the drug two hours before or six hours after iron or calcium supplements, or taking both together with a meal. Because the details differ between drugs in this class, people living with HIV should follow the label and the advice of their treating team.

Penicillamine, trientine and oral bisphosphonates are affected in similar ways. Penicillamine and trientine are metal binders used in conditions such as Wilson disease, and iron reduces their absorption, while alendronate and related drugs are poorly absorbed in the presence of food, minerals and other medicines. Their labels give strict timing instructions, which should be followed exactly.

Acid suppression works in the other direction. Stomach acid helps convert iron into a form that can be absorbed, so drugs that reduce acid can reduce iron absorption. In studies of people with hemochromatosis, proton pump inhibitors reduced absorption of dietary iron. In a large health-system cohort, long-term use of proton pump inhibitors and H2 blockers was associated with a higher risk of iron deficiency. This is an association, so it does not prove that the drug alone caused deficiency.

5. Theoretical/mechanistic interactions

Several interactions are plausible but poorly documented. They deserve caution, not alarm.

•      Mycophenolate: Early reports suggested iron lowered mycophenolate absorption, but later studies were inconsistent. Transplant teams may still advise separation.

•      Other chelating drugs: Medicines with chemical groups that bind metals could be affected, even without specific iron studies.

•      Additive stomach irritation: Iron tablets can irritate the stomach and esophagus. Combined with NSAIDs, bisphosphonates or other irritants, a larger effect is plausible, though not well quantified.

•      Antioxidant supplements and iron: Free iron can promote oxidative reactions in laboratory systems. Whether this changes the effect of antioxidant supplements in people is unknown.

•      Iron and gut bacteria: Unabsorbed iron may change the gut microbiome and the balance of bacteria. Human data are early, and the clinical significance is not established.

When an interaction is only theoretical, a pharmacist may still suggest a cautious spacing of doses, because spacing is cheap and low risk. That is a precaution and not evidence that harm occurs.

A useful way to think about theoretical risks is to ask what would happen if the interaction were real. For a drug with a narrow margin, such as a transplant or thyroid medicine, a hidden drop in absorption could matter, so caution is reasonable. For a drug with a wide margin, the same uncertainty matters much less.

6. Supplement-supplement interactions

Many people take iron with other supplements, so supplement interactions are common. Most involve competition for absorption.

•      Calcium: Calcium reduces absorption of both non-heme and heme iron. In classic meal studies, doses of 300 to 600 mg of calcium cut iron absorption by about half. Calcium supplements are therefore often separated from iron.

•      Zinc: High doses of zinc and iron can compete for absorption, mainly when taken together without food. At typical multivitamin amounts the effect is smaller.

•      Magnesium: Magnesium-containing antacids and supplements may reduce absorption, partly through acid neutralization and partly through binding.

•      Vitamin C: Vitamin C improves absorption of non-heme iron by keeping it in the ferrous form. This is a beneficial interaction for most people, but it is a concern in iron overload.

•      Polyphenol supplements: Green tea extract binds iron and reduces its absorption in meal studies. Case reports and laboratory work suggest curcumin in high doses may affect iron status. The human evidence for curcumin is limited.

•      Fiber and phytate supplements: Phytate, found in some fiber and mineral-binding products, inhibits non-heme iron absorption in a dose-dependent way.

Combination products complicate matters. A multivitamin with 18 mg of iron, 1,000 mg of calcium and zinc is formulated for balance, but it is not the same as an iron-only tablet in terms of iron absorption.

Timing matters for vitamin C too. Its benefit applies to iron in the same meal or dose, and the effect increases with the amount of vitamin C. It does not carry over to iron taken hours later.

7. Food interactions

Food has a larger effect on iron absorption than most people expect. The key idea is that non-heme iron, found in plants, eggs, dairy and supplements, is influenced by many dietary factors, while heme iron from meat and fish is absorbed more efficiently and is less affected.

Foods and drinks that reduce absorption

•      Tea and coffee: Polyphenols bind iron. In meal studies, tea and coffee reduced non-heme iron absorption substantially, with tea showing some of the largest reductions.

•      Dairy and calcium-rich foods: Calcium and casein reduce absorption.

•      Whole grains, legumes and nuts: Phytates bind iron. Soaking, sprouting and fermenting reduce phytate.

•      Soy protein: Soy products inhibit iron absorption beyond their phytate content.

•      Eggs: Egg proteins can reduce absorption of iron from the same meal.

Foods that improve absorption

•      Vitamin C-rich foods: Citrus, peppers, berries and tomatoes can offset the effect of inhibitors.

•      Meat, fish and poultry: The "meat factor" improves absorption of non-heme iron in the same meal.

Alcohol can raise iron absorption and liver iron in susceptible individuals, so people with hemochromatosis are usually advised to limit it. People with iron overload are also advised to avoid raw shellfish, because of infection risk.

Diet pattern also matters over the long term. Because non-heme iron is absorbed less efficiently than heme iron, the Institute of Medicine estimates that vegetarians need about 1.8 times as much dietary iron as people who eat meat. This is a nutritional point, and it does not by itself mean a supplement is needed.

Whether to take iron with food is a trade-off. Fasting maximizes absorption but increases stomach upset. Taking iron with a small meal reduces side effects but lowers absorption somewhat. People who need to take iron should discuss timing with their clinician.

8. Lab-test interference if relevant

Iron can influence laboratory results, and laboratory tests can mislead people who are taking iron.

•      Serum iron: Serum iron rises for several hours after an oral dose. Clinicians often ask patients to hold iron for about a day before a serum iron or transferrin saturation test, though practices differ.

•      Ferritin: Ferritin reflects stored iron but also rises with infection, inflammation, liver disease and some cancers. A normal ferritin during illness does not always rule out deficiency.

•      Hemoglobin: Hemoglobin responds in weeks, while ferritin takes months. A normal hemoglobin does not mean stores are replete.

•      Thyroid tests: If iron reduces levothyroxine absorption, thyroid-stimulating hormone may rise. This is a true change in thyroid control, not a test artifact.

•      Stool color and stool tests: Iron darkens stool and can look like bleeding. Most studies find that oral iron does not cause false-positive guaiac stool blood tests, but dark stool can be confusing. Black, tarry or foul-smelling stool, or any red blood, should be evaluated.

•      Imaging: Iron tablets can be visible on abdominal X-rays, which can matter in suspected overdose.

Tell the clinician and the laboratory that you take iron before any blood test, and ask whether to pause it.

Test interpretation can also depend on timing. Hepcidin and serum iron change over the day, and recent doses alter results. Using the same laboratory and a similar time of day for repeat tests makes comparisons more reliable.

9. Severity/strength of evidence

Severity and strength of evidence are different things. An interaction can be well proven but minor, or poorly proven but potentially serious. The table below rates the interactions discussed on this page using a simple editorial scale, not a formal grading system.

Interaction	Strength of evidence	Notes
Iron with levothyroxine	Strong	Documented effect on thyroid control
Iron with fluoroquinolones or tetracyclines	Strong	Treatment failure possible if taken together
Iron with levodopa, methyldopa	Moderate	Small studies; individual effect varies
Iron with HIV integrase inhibitors	Strong	Labeling gives specific advice
Acid-reducing drugs lowering iron absorption	Moderate	Cohort and absorption data; association, not proof of cause
Calcium, tea, coffee, phytate reducing iron absorption	Strong	Consistent meal studies; effect varies by meal
Zinc and iron competition	Moderate	Mainly at high doses without food
Curcumin and iron status	Weak	Case reports and laboratory work
Mycophenolate, other chelating drugs	Weak	Mechanistic or conflicting data
Antioxidant supplements and iron	Weak	Laboratory rationale only

 

"Strong" means consistent human data or explicit labeling. "Moderate" means some human data with limitations. "Weak" means case reports, laboratory work or mechanism only. Severity is also context dependent. A missed antibiotic dose may matter more in a serious infection than in a mild one, and a lower levothyroxine effect matters more in a person with limited thyroid reserve.

10. Who should consult a clinician

Anyone who takes prescription medicines and wants to take iron should check with a pharmacist first. Consultation is especially important in the following situations.

•      Taking levothyroxine, antibiotics, levodopa, methyldopa, HIV medicines, bisphosphonates, penicillamine, trientine or transplant medicines.

•      Using proton pump inhibitors, H2 blockers or regular antacids.

•      Having hemochromatosis, thalassemia, sickle cell disease with transfusions, or any condition of iron overload.

•      Being pregnant or breastfeeding, or giving iron to a child.

•      Having chronic kidney disease, inflammatory bowel disease, heart failure, liver disease or a history of gastrointestinal bleeding or surgery.

•      Having unexplained iron deficiency, particularly in men and in postmenopausal women, since it can signal blood loss.

•      Having blood tests, surgery or scans scheduled.

•      Taking several supplements at once, particularly high-dose calcium, zinc or polyphenol products.

Seek urgent care for suspected iron overdose, severe stomach pain, vomiting blood or black tarry stool. Keep iron out of reach of children.

11. FAQ

Can I take iron with my levothyroxine?

Iron can lower levothyroxine absorption, and labeling advises separating them by several hours. Ask the prescriber or pharmacist for the schedule that fits your regimen, and do not change doses on your own.

Does iron interact with antibiotics?

Yes, with some. Fluoroquinolones and tetracyclines bind iron and may be less effective if taken at the same time. Check the label of the specific antibiotic.

Can I take iron and calcium together?

Calcium reduces iron absorption in meal studies, so many guidelines advise separating them. Some multivitamins combine them for convenience.

Does coffee or tea affect iron?

Yes. Polyphenols in tea and coffee reduce non-heme iron absorption, so these drinks are usually kept away from iron-rich meals or supplements.

Do acid reflux medicines affect iron?

They can. Lower stomach acid reduces non-heme iron absorption, and long-term use is associated with a higher risk of iron deficiency. Do not stop reflux medicine without medical advice.

Does vitamin C help iron?

Vitamin C improves non-heme iron absorption. It is not appropriate to add vitamin C in people with iron overload.

Will iron affect my blood tests?

Yes, it can. Serum iron rises after a dose and ferritin is affected by inflammation. Tell your clinician you take iron before tests.

12. References

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2.      Campbell NR, Hasinoff BB, Stalts H, Rao B, Wong NC. Ferrous sulfate reduces thyroxine efficacy in patients with hypothyroidism. Ann Intern Med. 1992;117:1010-1013.

3.      Campbell NR, Rankine D, Goodridge AE, Hasinoff BB, Kara M. Sinemet-ferrous sulphate interaction in patients with Parkinson's disease. Br J Clin Pharmacol. 1990;30:599-605.

4.      Campbell NR, Paddock V, Sundaram R. Alteration of methyldopa absorption, metabolism, and blood pressure control caused by ferrous sulfate and ferrous gluconate. Clin Pharmacol Ther. 1988;43:381-386.

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8.      Hallberg L, Brune M, Rossander L. Iron absorption in man: ascorbic acid and dose-dependent inhibition by phytate. Am J Clin Nutr. 1989;49:140-144.

9.      Hurrell RF, Reddy M, Cook JD. Inhibition of non-haem iron absorption in man by polyphenolic-containing beverages. Br J Nutr. 1999;81:289-295.

10.   Morck TA, Lynch SR, Cook JD. Inhibition of food iron absorption by coffee. Am J Clin Nutr. 1983;37:416-420.

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12.   Smith TJ, Ashar BH. Iron deficiency anemia due to high-dose turmeric. Cureus. 2019;11(1).

13.   Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academies Press; 2001.

14.   National Institutes of Health, Office of Dietary Supplements. Iron: Fact Sheet for Health Professionals. Bethesda, MD: NIH.

15.   Pasricha SR, Tye-Din J, Muckenthaler MU, Swinkels DW. Iron deficiency. Lancet. 2021;397:233-248.

16.   U.S. Food and Drug Administration. Prescribing information for levothyroxine, ciprofloxacin, dolutegravir and alendronate (drug labels, current versions at DailyMed).