Iron Sulfate: Dosage, Timing & Interactions

Check it against something

Evidence level A

Iron Sulfate with:

99 out of 100

Works better together Compatible. Timing differs, so follow each supplement's own window.

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What it does

mechanism and evidence for each claim

Highest elemental iron content

Contains 20% elemental iron, more than most other forms

Simple sulfate structure provides maximum iron per gram Evidence A-grade Per dose benefit

Proven anemia treatment efficacy

Gold standard for treating iron deficiency anemia

High bioavailable iron rapidly corrects deficiency Evidence A-grade 4-12 weeks

Most cost-effective option

Least expensive way to supplement with iron

High elemental content reduces cost per mg of iron Evidence A-grade Economic benefit

Extensive clinical research

Most studied iron form with decades of safety data

Standard form used in clinical trials and medical practice Evidence A-grade Historical evidence

Rapid hemoglobin improvement

Quickly raises hemoglobin and hematocrit levels

Provides readily available iron for red blood cell production Evidence A-grade 2-8 weeks

Or a different form of the same thing

the comparison people search most

Iron Sulfate vs Iron Bisglycinate absorption 20 against 90 · $8 against $30 a month 90% Iron Sulfate vs Iron Fumarate absorption 20 against 25 · $8 against $18 a month 25% Iron Sulfate vs Heme Iron absorption 20 against 85 · $8 against $120 a month 85%

All Iron forms ranked by absorption →

Every pair we checked

12 combinations scored by the engine

Iron Sulfate + Turmeric May reduce iron absorption Needs attention 61

Iron Sulfate + Caffeine No documented interaction either way No known interaction 70

Iron Sulfate + Creatine Monohydrate No documented interaction either way No known interaction 70

Iron Sulfate + Calcium Carbonate No documented interaction either way No known interaction 70

Iron Sulfate + Whey Protein No documented interaction either way No known interaction 70

Iron Sulfate + Lactase No documented interaction either way No known interaction 70

Iron Sulfate + Bovine Collagen No documented interaction either way No known interaction 70

Iron Sulfate + DHA No documented interaction either way No known interaction 70

Iron Sulfate + Fish Oil (EPA/DHA) No documented interaction either way No known interaction 70

Iron Sulfate + Copper Bisglycinate High iron may compete with copper absorption Needs attention 82

Iron Sulfate + Vitamin D3 Significantly enhances iron absorption Works better together 94

Iron Sulfate + Vitamin C (Ascorbic Acid) Significantly enhances iron absorption Works better together 99

Dosage

Empty stomach if tolerated

Daily65-200 mg

Maintenance30-65 mg elemental iron daily

Therapeutic100-200 mg elemental iron daily

Anemia treatment150-300 mg elemental iron daily (divided)

Elemental ironContains ~20% elemental iron

Upper limit 45 mg NIH ODS

Before you take it

Pregnancycommonly recommended

VeganYes

When to expect it

First Effects1-2 weeks for energy improvements, 2-4 weeks for hemoglobin rise

Peak Benefits8-16 weeks for complete iron deficiency correction

Deficiency DevelopmentMonths to years depending on iron stores

Toxicity OnsetPossible with excessive doses, especially dangerous for children

How to measure it

$50-150

MarkerHemoglobin, hematocrit, serum ferritin, iron saturation

OptimalHemoglobin: 12-15.5 g/dL (women), 13.5-17.5 g/dL (men), Ferritin: 15-200 ng/mL

Deficient belowHemoglobin: <12 g/dL (women), <13.5 g/dL (men), Ferritin: <15 ng/mL

FrequencyEvery 4-8 weeks during treatment, then every 3-6 months

What people actually reported to the FDA

CAERS, 340 reports naming it as the suspect

Most reported effects

Vomiting 33

Dyspnoea 31

Diarrhoea 28

Nausea 24

Hypersensitivity 23

Named as the suspect 340 reports of 1,000+ that mention it at all

Serious outcome 84% hospitalisation, emergency room or worse

Other Serious or Important Medical Event228

Hospitalization85

Visited Emergency Room65

Reports are voluntary and unverified — they record what someone experienced while taking something, not what the compound caused. Counts skew towards products people take a lot of, and a serious outcome is more likely to be reported than a mild one, so these are not rates. How we filter them →

What actually reaches you

The label counts the carrier, your body does not

Elemental iron 20.1% of 278.01 g/mol

Absorption Low 20 of 100 · poorly absorbed relative to other forms

Delivered daily 5.3 mg

Cost per 100 mg delivered $5.01 comparative — uses the absorption score, not a measured percentage

A 500 mg capsule of Iron Sulfate contains 101 mg of iron. How much of that crosses into your blood is not measured for this form — the absorption score ranks it against other forms, it is not a share of the dose. How this is calculated →

Works better with

3 documented

+

Vitamin C

Significantly enhances iron absorption

Reduces ferric iron to absorbable ferrous form · level A

+

B Vitamins

B12, B6, and folate support red blood cell formation

Cofactors for hemoglobin and red blood cell synthesis · level A

+

Copper

Copper required for iron utilization

Copper needed for iron transport and utilization · level A

What not to take with Iron Sulfate

3 documented

!

Calcium Zinc Magnesium

These minerals can reduce iron absorption

Competition for absorption transporters · moderate significance

!

Coffee Tea Tannins

Tannins significantly reduce iron absorption

Tannins bind iron making it unavailable for absorption · high significance

!

Fiber Phytates

Dietary fiber and phytates can bind iron

Chelation reduces iron bioavailability · moderate significance

Medication interactions

Discuss these with a pharmacist before combining

levothyroxine Major

Iron significantly reduces thyroid hormone absorption

What to do: Take thyroid medication 4+ hours before iron

tetracycline-quinolone-antibiotics Major

Iron dramatically reduces antibiotic absorption

What to do: Space doses 2-4 hours apart

carbidopa-levodopa Moderate

Iron may reduce Parkinson's medication effectiveness

What to do: Space doses 2+ hours apart

proton-pump-inhibitors Moderate

PPIs reduce iron absorption from supplements

What to do: Take iron with vitamin C, consider alternative forms

Available forms

bioavailability compared

Ranks 4 of 4 among iron forms. Iron Bisglycinate absorbs better — 90%. Compare all forms →

Ferrous Sulfate (Tablets/Capsules) 20

Ferrous Sulfate (Tablets/Capsules): Highest elemental iron, Lowest cost, Most research, Medical standard

Food sources

before you supplement

Red meat 2-3 mg per 3 oz serving · 25

Liver 18 mg per 3 oz serving · 25

Fortified cereals 4-18 mg per serving · 10

Spinach (cooked) 6 mg per cup · 5

Too little

deficiency signs

Fatigue and weakness
Iron deficiency anemia
Pale skin, nails, and inner eyelids
Shortness of breath
Cold hands and feet
Brittle or spoon-shaped nails
Restless leg syndrome

Too much

toxicity signs

Nausea and vomiting
Abdominal pain and constipation
Iron poisoning (high doses)
Organ damage (severe cases)
Interference with other mineral absorption

Who benefits most

iron-deficiency-anemia

Most effective and proven treatment for iron deficiency anemia

100-200 mg daily (divided doses)

budget-conscious-iron-needs

Most affordable way to supplement with iron

65-130 mg daily

severe-iron-deficiency

High elemental content for rapid correction

150-300 mg daily (medical supervision)

medical-treatment-compliance

Standard medical treatment with established protocols

As prescribed by healthcare provider

basic-iron-supplementation

Simple, proven iron supplementation

65-100 mg daily

Where to buy it

compare forms first

Look for Iron Sulfate at 65-200 mg per serving. The form that matters here is Ferrous Sulfate (Tablets/Capsules).

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What else affects it

Beyond other supplements

!

Coffee tea tannins

Tannins significantly reduce iron absorption

Tannins bind iron making it unavailable for absorption

!

Fiber phytates

Dietary fiber and phytates can bind iron

Chelation reduces iron bioavailability

How it works

Ferrous (Fe2+) form is readily absorbed in duodenum
Requires stomach acid for optimal dissolution and absorption
Absorbed via divalent metal transporter (DMT1)
Competes with other metals for absorption pathways
Transported by transferrin to bone marrow for hemoglobin synthesis
Stored as ferritin in liver and other tissues

Key findings

what the evidence supports

Most effective form for treating iron deficiency anemia
Standard treatment recommended by medical organizations worldwide
Higher rates of side effects but proven clinical efficacy
Cost-effective option for iron deficiency correction

Sources: NIH Examine.com · data reviewed 2026-08-02

Compiled by Denis, who maintains this database and holds no medical qualification — every figure here is sourced or derived, never asserted. How we calculate it →

Common questions

What are the benefits of Iron Sulfate?

Documented effects: Highest elemental iron content; Proven anemia treatment efficacy; Most cost-effective option; Extensive clinical research. Contains 20% elemental iron, more than most other forms

How much Iron Sulfate should you take per day?

The common daily range is 65-200 mg. By goal — maintenance: 30-65 mg elemental iron daily; therapeutic: 100-200 mg elemental iron daily; anemia treatment: 150-300 mg elemental iron daily (divided); elemental iron: Contains ~20% elemental iron.

When is the best time to take Iron Sulfate?

Empty stomach if tolerated. First effects are typically reported within 1-2 weeks for energy improvements, 2-4 weeks for hemoglobin rise.

What are the side effects of Iron Sulfate?

At excessive doses: Nausea and vomiting, Abdominal pain and constipation, Iron poisoning (high doses), Organ damage (severe cases), Interference with other mineral absorption. Safety rating at normal doses is 6 out of 10.

What should you not take with Iron Sulfate?

Separate it from Calcium Zinc Magnesium, Coffee Tea Tannins, Fiber Phytates by two to four hours. These minerals can reduce iron absorption

Does Iron Sulfate interact with medications?

Documented interactions with levothyroxine, tetracycline-quinolone-antibiotics, carbidopa-levodopa, proton-pump-inhibitors. Discuss these with a pharmacist before combining.

How much Iron Sulfate is too much?

The tolerable upper intake level is 45 mg per day for adults, per NIH ODS. Above that, the risk of adverse effects rises: Nausea and vomiting, Abdominal pain and constipation, Iron poisoning (high doses).

How do you know if you need Iron Sulfate?

The marker is Hemoglobin, hematocrit, serum ferritin, iron saturation, optimal range Hemoglobin: 12-15.5 g/dL (women), 13.5-17.5 g/dL (men), Ferritin: 15-200 ng/mL. Common deficiency signs: Fatigue and weakness, Iron deficiency anemia, Pale skin, nails, and inner eyelids, Shortness of breath.