Iron

Best for

Prevent anemia through pregnancy

Large effect, needs confirmation for 2–52 weeks · 18 meta-analyses , n=84.9k

47 papers · 5 claims · 86 outcomes scored · 5 positive

Outcomes

What iron actually does, by outcome

Each row is one outcome with effect size, evidence base, the dose that worked in trials, and time to first effect. Magnitude tiers come from native-unit MCID where available, Cohen's d otherwise.

Outcome Effect size Evidence Dose Weeks Rank

Prevent anemia through pregnancy Large effect, needs confirmation

Keeps red blood cell levels up when pregnancy drains them fastest.

27 meta-analyses n=85k 2–1000 mg 2–52 wk #2/5

22272750·22419305·22777991·24130243 +23 more

large

27 meta-analyses n=85k Meta-analyzed I²=100%

2–1000 mg

2–52 wk

#2 /5

Rebuild iron stores when depleted Proven strong benefit

Raises circulating iron, fills reserves, and feeds iron-hungry tissues.

18 meta-analyses n=44k 1–400 mg 6–52 wk

28510680·38147281·39469104·40464050 +14 more

large

18 meta-analyses n=44k Meta-analyzed I²=99%

1–400 mg

6–52 wk

—

Reduce everyday fatigue Likely benefit

Less of that heavy, worn-out feeling that makes simple tasks feel like a chore.

8 meta-analyses n=986 14–1000 mg 4–12 wk #1/44

12763985·22272750·22777991·29626044 +4 more

moderate

8 meta-analyses n=986 Meta-analyzed

14–1000 mg

4–12 wk

#1 /44

Calm restless legs at night Likely benefit

Quiets the crawling, tingling urge to move when your body needs to be still.

2 meta-analyses n=638 100–1000 mg 10 wk #1/3

30609006·32380660

moderate

2 meta-analyses n=638 Meta-analyzed I²=80%

100–1000 mg

10 wk

#1 /3

Build more oxygen-rich red blood cells Proven modest benefit

More red cells loaded with more hemoglobin reach every muscle and organ.

27 meta-analyses n=85k 2–1000 mg 2–52 wk #1/7

22272750·22419305·22777991·24130243 +23 more

small

27 meta-analyses n=85k Meta-analyzed I²=100%

2–1000 mg

2–52 wk

#1 /7

Outcome	Effect	Evidence	Dose	Weeks	Rank
Prevent anemia through pregnancy Large effect, needs confirmation	large	27 meta-analyses n=85k Meta-analyzed	2–1000 mg	2–52 wk	#2/5
Rebuild iron stores when depleted Proven strong benefit	large	18 meta-analyses n=44k Meta-analyzed	1–400 mg	6–52 wk	—
Reduce everyday fatigue Likely benefit	moderate	8 meta-analyses n=986 Meta-analyzed	14–1000 mg	4–12 wk	#1/44
Calm restless legs at night Likely benefit	moderate	2 meta-analyses n=638 Meta-analyzed	100–1000 mg	10 wk	#1/3
Build more oxygen-rich red blood cells Proven modest benefit	small	27 meta-analyses n=85k Meta-analyzed	2–1000 mg	2–52 wk	#1/7

Buy well

Recommended Iron products

Real products that dose Iron where the research does, in a clean formulation, from brands we've audited. We only list ones we'd stand behind.

Chosen for adequate Iron dosing vs. the studied range, a clean formulation (grade A–C), and independent brand-quality audits. Not sponsored.

Risk profile

Adverse events and known drug interactions

Safety events

Serious adverse events (any) severe

Serious adverse events (hospitalization or death) severe

Altered neurodevelopment / long-term neurodevelopmental impairment severe

constipation mild

abdominal pain mild

gastrointestinal discomfort mild

increased appetite mild

dark stools mild

Drug interactions

Antineoplastic Agents major decreases effect

Metformin major decreases concentration

Aspirin moderate decreases concentration

Co-studied with

Supplements that share evidence with iron

Sources

Generated August 14, 2026

Iron

What iron actually does, by outcome

Recommended Iron products

Adverse events and known drug interactions

Supplements that share evidence with iron

More evidence for Iron

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Iron

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More evidence for Iron

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NewCaffeine

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Best Supplements for Brain Fog and Mental Clarity, Ranked by Evidence

The 10 Best Supplements for Memory, Ranked by Evidence

Iron for Cognitive Function: A Systematic Evidence Review

Sleep: evidence map across 37 supplements

Caffeine