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Reviewed by the Scan Dose Research Team and Clinical Advisory Board

Iron

STRONG EVIDENCEMineralLast updated April 5, 2026

SCAN DOSE SUMMARY

Iron is an essential mineral that carries oxygen in your blood. Unlike most supplements on this list, iron is one you should NOT take unless you're deficient or a healthcare provider recommends it. Our research, from 9 RCTs, 13 meta-analyses, and 107,000+ participants, confirms iron supplementation corrects deficiency and anemia — but excess iron increases oxidative stress and can cause serious organ damage. This is a "test first, supplement second" ingredient.

EVIDENCE GRADES

Risk of Hospitalization for Heart FailureStrong — iron reduces hospitalization in heart failure with iron deficiency
A
Ferritin increaseModerate
B
Hemoglobin increaseModerate
B
Fatigue reductionModerate — in iron-deficient individuals
B
Exercise capacityModerate — in iron-deficient individuals
B

WHAT IT DOES

  • Corrects iron deficiency anemia — Primary indication. Restores hemoglobin and oxygen-carrying capacity.
  • Reduces fatigue in iron-deficient individuals — Grade B evidence. Only works if you're actually deficient.
  • Reduces heart failure hospitalizations — Grade A evidence in iron-deficient HF patients.
  • Supports exercise performance — Grade B evidence, specifically in iron-deficient athletes (common in female athletes).
  • Does NOT benefit iron-sufficient people — Excess iron increases oxidative stress and may damage organs.

OPTIMAL DOSAGE

  • RDA (adult males): 8mg/day
  • RDA (adult females, 19-50): 18mg/day (higher due to menstrual losses)
  • RDA (pregnant women): 27mg/day
  • For deficiency treatment: 1-300mg elemental iron/day, divided doses
  • UL (adults): 45mg/day (based on GI side effects)
  • Best forms: Ferrous bisglycinate (best tolerated, good absorption), ferrous sulfate (most studied, cheap, more GI effects), ferric maltol (better tolerated)
  • AVOID taking with: Phytate-rich foods (grains, legumes), dairy/calcium, tea/coffee, eggs
  • Timing: Best on empty stomach for absorption, but taking with food reduces nausea. Alternate-day dosing may improve absorption and reduce side effects.
  • KEY: Get tested first. Iron is the one supplement where blind supplementation can cause harm.
Scan a supplement containing Iron

DRUG INTERACTIONS

Tetracycline antibioticsSevere

Mutual absorption reduction

Take tetracyclines 2 hours before or 4 hours after iron.

Fluoroquinolone antibioticsSevere

Reduces antibiotic absorption

Take fluoroquinolones 2 hours before or 4-8 hours after iron.

Carbamazepine/CyclosporineSevere

Reduces drug absorption

Separate administration. Monitor drug levels.

CefdinirSevere

Reduces drug absorption

Separate dosing times.

Integrase inhibitors (dolutegravir)Severe

Reduces drug absorption

Separate by 4+ hours.

LevothyroxineModerate

Reduces drug absorption

Take levothyroxine 2+ hours before iron.

PenicillamineModerate

Reduces drug absorption

Separate administration.

Acid-reducing drugs (PPIs, H2 blockers, antacids)Moderate

Reduces iron absorption

May need higher iron doses or alternate-day dosing.

LevodopaModerate

Reduces drug absorption

Separate by 2+ hours.

CalciumModerate

Reduces iron absorption

Take at separate times if using calcium citrate.

CaptoprilModerate

Reduces drug absorption

Separate by 2+ hours.

MethyldopaModerate

Reduces drug absorption

Separate by 2+ hours.

MagnesiumModerate

Reduces iron absorption

Take at separate times.

Yerba MateModerate

Reduces iron absorption

Don't take iron with yerba mate.

Curcumin/TurmericModerate

Mixed evidence

Monitor iron levels if taking high-dose curcumin.

ZincMinor

Mutual absorption reduction

Take at separate times if concerned.

AcetaminophenMinor

Reduces absorption

No action needed.

SAFETY PROFILE

Side Effects

  • Very common (even at small doses): Constipation, diarrhea, nausea, dark/black stools, abdominal pain, vomiting, heartburn, flatulence
  • Less common (tablet formulations): Upper GI ulceration (esophageal/stomach erosion)
  • IV iron: Infusion reactions (flushing, hives, chest pressure, anaphylaxis), hypophosphatemia
  • Toxicity (≥20mg/kg body weight): Vomiting, GI bleeding, liver necrosis, multiorgan failure, shock, metabolic acidosis, coma, death. Leading cause of poisoning deaths in children under 6.

Drug Interactions

△ KEY RULE: Iron chelates many drugs in the gut. Take iron at least 2 hours before or 3 hours after medications.

Nutrient Depletions (Drugs That Deplete Iron)

  • PPIs — prolonged use (1+ years) increases iron deficiency risk
  • H2 antagonists — associated with increased iron deficiency risk
  • Calcium channel blockers — one study correlated with iron deficiency in heart failure
  • Aspirin — associated with iron deficiency anemia (weak evidence)
  • Grape seed extract — high doses (2,500mg/day) may reduce serum iron

Precautions

  • Pregnancy: Caution. Supplementation at appropriate doses is safe and often recommended. Severe toxicity (overdose) can cause miscarriage, preterm delivery, and maternal death.
  • Breastfeeding: Safe. Breast milk iron is tightly regulated and not greatly influenced by supplementation.
  • Children: HIGH DANGER. Iron toxicity is a leading cause of poisoning deaths in children under 6. Store safely. Toxicity at ≥20mg/kg bodyweight.
  • Hemochromatosis: AVOID. Genetic disorder causing iron overload → liver cirrhosis, heart disease, cancer.
  • GI ulcers: Iron tablets can worsen pre-existing ulcers. Use liquid iron or IV if needed.
  • General population: Do NOT supplement unless deficient. Excess iron increases free radical production, oxidative stress, and potential organ damage.

WADA Status

Not Prohibited. Not on the 2026 WADA list.

WHO SHOULD BE CAREFUL

HOW SCAN DOSE SCORES THIS

Present in proper dose (8-18mg depending on gender, bioavailable form):✅ Green flag — IF the target user needs iron (menstruating women, athletes, deficient individuals)
Present without medical indication:⚠️ Yellow flag — iron should not be supplemented blindly
High dose (>45mg/serving) without medical supervision:🔴 Red flag — exceeds UL, toxicity risk
In a proprietary blend:🔴 Red flag — iron dose MUST be known for safety
Iron oxide form:⚠️ Yellow flag — poorest absorption, often used as colorant not supplement
In a children's product without childproof packaging:🔴 Red flag — leading cause of pediatric poisoning deaths
Combined with antibiotics in same product:🔴 Red flag — chelation reduces antibiotic effectiveness

CLINICAL REFERENCES

1.

Alternate-day iron dosing results in better fractional absorption than daily dosing.

Stoffel NU et al. Iron absorption from oral iron supplements given on consecutive versus alternate days and as single morning doses versus twice-daily split doses.. Lancet Haematol (2017). PMID: 33232588

2.

Single daily dose in the morning maximizes absorption; twice-daily dosing paradoxically reduces total absorption.

Moretti D et al. Oral iron supplements increase hepcidin and decrease iron absorption from daily or twice-daily doses.. Blood (2015). PMID: 29323692

3.

Comprehensive review of iron deficiency pathophysiology, diagnosis, and treatment — the go-to reference for iron metabolism.

Camaschella C. Iron deficiency.. Blood (2019). PMID: 31447418

4.

Iron deficiency affects >1 billion people globally. Ferritin <30 μg/L is the most useful single test for iron deficiency.

Pasricha SR et al. Iron deficiency.. Lancet (2021). PMID: 32098519

5.

IV iron at discharge reduced heart failure hospitalizations by 26%.

Ponikowski P et al. Ferric carboxymaltose for iron deficiency at discharge after acute heart failure.. Lancet (2020). PMID: 30879237

RELATED RESEARCH

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Quality Testing Intelligence

Based on independent third-party laboratory analysis

Category pass rate: ~85% pass rate. Form and absorption are more important than label accuracy.

Scan Your Iron SupplementBrowse all ingredients

Reviewed by the Scan Dose Research Team and Clinical Advisory Board | Last updated: April 5, 2026

Not medical advice. Based on published clinical research and systematic reviews.

Safety

Iron: Drug Interactions

Use with caution

Moderate interactions. Monitoring, timing separation, or dose adjustment may be required.

  • Levothyroxine

    Iron binds levothyroxine in the gut.

    RiskSubtherapeutic thyroid levels.
    ActionSeparate by 4 or more hours.

    Source: FDA label

  • Antacids, PPIs, H2 blockers

    Reduced stomach acid impairs iron absorption.

    RiskIron deficiency persists.
    ActionTake iron on an empty stomach or with vitamin C. Separate from antacids by 2 or more hours.

    Source: Clinical standard

  • Tetracycline and doxycycline

    Iron chelates the antibiotic.

    RiskAntibiotic treatment failure.
    ActionSeparate by 2 to 3 hours.

    Source: FDA label

  • Fluoroquinolones

    Iron chelates the antibiotic.

    RiskAntibiotic treatment failure.
    ActionTake 2+ hours before or 6+ hours after the antibiotic.

    Source: FDA label

  • Levodopa (Parkinson's)

    Iron reduces levodopa absorption.

    RiskWorsened Parkinson's symptoms.
    ActionSeparate by 2 or more hours.

    Source: Clinical pharmacology

  • Methyldopa

    Iron reduces absorption.

    RiskSubtherapeutic blood pressure control.
    ActionSeparate by 2 or more hours.

    Source: FDA label

Timing Separation Rules

  • Levothyroxine4 hours
  • Tetracycline / fluoroquinolone antibiotics2 to 3 hours
  • Antacids and PPIs2 hours

Educational information only. This is not medical advice. These statements have not been evaluated by the FDA. Talk to your prescriber before starting, stopping, or combining any supplement with prescription medication.

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