Does taking iron fix iron-deficiency anemia?

Yes, in the trials it does. A Cochrane review of 67 randomized trials in 8506 menstruating women found daily iron cut the risk of still being anemic at the end by 61 percent (risk ratio 0.39) and raised hemoglobin by 5.3 g/L. In children and teenagers with confirmed iron-deficiency anemia, 28 studies found a rise of about 2 g/dL. The price is the gut: in the same Cochrane review constipation roughly doubled.

Established. Oral iron raises hemoglobin and lowers anemia. That is the finding of Cochrane reviews in menstruating women and in pregnancy, rated moderate to high quality for these outcomes. It is one of the few nutrient claims where several large meta-analyses agree on direction.

What the trials found

Menstruating women

The largest review pooled 67 trials of daily iron, taken at least five days a week, in women aged 12 to 50. Anemia at the end of the trial had a risk ratio of 0.39 (95% CI 0.25 to 0.60, 10 studies, 3273 women, moderate quality). Hemoglobin rose by 5.30 g/L (4.14 to 6.45) across 51 studies and 6861 women, on high quality evidence. The abstract does not give how many women started anemic, so the 61 percent cannot be turned into a count here. Only 10 of the 67 trials were at low risk of bias. Only one of them measured iron-deficiency anemia specifically, which is the exact question on this page.

Pregnancy

A 2024 Cochrane review of 57 trials in 48,971 pregnant women looked at daily iron given to prevent anemia, so most women were not anemic at the start. Iron-deficiency anemia at term fell from 18.4 percent to 5.0 percent (risk ratio 0.41, 7 trials, 2704 women, moderate certainty). Anemia of any cause at term had a risk ratio of 0.30, on low certainty evidence from 14 trials. The review found little or no difference in preterm birth or newborn deaths.

For pregnant women who already have iron-deficiency anemia, a 2026 meta-analysis of 29 trials compared intravenous iron with tablets. Hemoglobin at delivery was 0.59 g/dL higher with the drip (95% CI 0.31 to 0.87, 15 studies), and transfusions fell by 37 percent (risk ratio 0.63, 14 studies). The abstract gives no baseline transfusion rate, so the absolute gain is unknown. The benefit was largest when hemoglobin started at 9 g/dL or lower. One trial in the earlier version of this analysis was retracted and has been removed.

Children and teenagers

Across 28 studies in 8829 children and teenagers up to 19 with ferritin-confirmed iron-deficiency anemia, from 16 countries, iron for at least 30 days raised hemoglobin by 2.01 g/dL (95% CI 1.48 to 2.54). The authors pooled mixed designs as standardized effects, so that g/dL figure is approximate. Doses under 5 mg/kg a day showed favorable trends. The abstract does not say how many of these studies were randomized trials.

Every day or every other day

Unsettled. Taking iron every other day is often recommended to spare the gut. Across 11 trials in 1014 people with iron-deficiency anemia, daily dosing raised hemoglobin 0.28 g/dL more, an edge that did not reach significance (95% CI -0.01 to 0.56). Side effects were similar overall (risk ratio 1.07), and metallic taste was more frequent with daily iron. The reviewers rated most of this very low certainty. In a trial of 88 pregnant women with mild anemia, hemoglobin rose 0.8 g/dL in 6 weeks on daily ferrous sulfate and 0.5 g/dL on double doses every other day. The adjusted difference of 0.3 g/dL did not reach significance either, in a small trial with unbalanced groups.

Who should be careful

The gut is where iron costs something. In the Cochrane review in menstruating women, hard stools or constipation had a risk ratio of 2.07 (95% CI 1.35 to 3.17, 8 trials, 1036 women) and loose stools 2.13 (6 trials, 604 women), on high quality evidence. Nausea did not differ clearly. Across 43 trials in 6831 adults, ferrous sulfate raised the odds of stomach and bowel side effects 2.32 times against placebo and 3.05 times against intravenous iron. That is an odds ratio, and the review found no clear link with dose.

Not for everyone. Iron tablets are dangerous to small children. The NIH notes that a single intake above 20 mg/kg can cause intestinal necrosis, so the bottle belongs out of reach. Iron also interacts with levodopa and levothyroxine, and proton pump inhibitors can reduce how much iron you absorb. The NIH gives no sizes for these interactions.

In children living where malaria is intense, a 2026 Cochrane review of 40 trials found iron did not raise clinical malaria overall (risk ratio 0.93, high certainty). Where malaria prevention and care were missing, it may raise clinical malaria by about 15 percent (risk ratio 1.15, 7 trials, 19,754 children), on low certainty evidence. That caution applies only to those settings.

We have no card on iron overload, so this page does not cover who should not take iron at all.

What expert bodies say

The NIH Office of Dietary Supplements sets the adult upper limit for iron at 45 mg a day, and 40 to 45 mg for infants, children and teenagers. The limit was set on the gut effects of iron salts. The NIH notes that doctors may prescribe more to treat anemia, under supervision.

On iron in pregnancy, US bodies disagree. ACOG recommends low-dose iron from the first trimester to lower anemia at delivery. The USPSTF finds the evidence insufficient for routine screening and supplements in pregnant women without symptoms. The disagreement is about women who are not anemic. Both agree that established iron-deficiency anemia should be treated.

How we searched

What would change this answer

• Head-to-head trials of intravenous against oral iron outside pregnancy. The firm comparison on this page is in pregnant women only.
• Larger trials of alternate-day dosing that measure what people feel, such as fatigue, as well as hemoglobin. The current evidence on schedule is very low certainty, and the best dose and schedule for adults is not settled.
• Trials in menstruating women that report iron-deficiency anemia itself. Only one did. No trial in that review reported deaths.
• Few trials are running. ClinicalTrials.gov showed one completed trial, on a probiotic to make iron easier to tolerate, with no results posted.

The rest of what iron does, how much you need and where it comes from in food is in the iron guide.

Sources

1. ev-irana-01 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of randomized trials · n = 8506
   Women receiving iron were significantly less likely to be anaemic at the end of intervention compared to women receiving control (risk ratio (RR) 0.39 (95% confidence interval (CI) 0.25 to 0.60, 10 studies, 3273 women, moderate quality evidence).
   
   Who: menstruating women aged 12 to 50, daily oral iron at least five days a week vs control or placebo
   Effect: anemia at end of intervention RR 0.39 (95% CI 0.25-0.60; 10 studies, 3273 women); hemoglobin MD 5.30 g/L (4.14-6.45; 51 studies, 6861 women)
   Certainty: Moderate quality for anemia, high for hemoglobin; only 10 of 67 trials at low risk of bias; only one study reported iron-deficiency anemia specifically.
   Cochrane Database Syst Rev, 2016 · checked 2026-10-06 · we read the abstract
2. ev-irana-02 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of randomized trials · n = 1036
   eight studies recruiting 1036 women identified an increased prevalence of hard stools/constipation (RR 2.07, 95% CI 1.35 to 3.17, high quality evidence).
   
   Who: menstruating women in randomized trials of daily oral iron
   Effect: hard stools or constipation RR 2.07 (95% CI 1.35-3.17; 8 studies, 1036 women); loose stools RR 2.13 (1.10-4.11; 6 studies, 604 women); nausea RR 1.19 (0.78-1.82)
   Certainty: High-quality evidence for bowel effects; adherence did not visibly differ between iron and control.
   Cochrane Database Syst Rev, 2016 · checked 2026-10-06 · we read the abstract
3. ev-irana-03 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of randomized trials · n = 48971
   probably reduces maternal iron-deficiency anaemia at term (5.0% versus 18.4%; RR 0.41, 95% CI 0.26 to 0.63; 7 trials, 2704 women; moderate-certainty evidence)
   
   Who: pregnant women, daily oral iron vs placebo or no iron, 57 trials
   Effect: maternal anemia at term RR 0.30 (95% CI 0.20-0.47; 14 trials, 13,543 women, low certainty); iron-deficiency anemia at term RR 0.41 (0.26-0.63; 7 trials, 2704 women, moderate certainty)
   Certainty: Prevention in pregnancy, not treatment of established anemia; low to moderate certainty; little or no difference in preterm birth or neonatal death.
   Cochrane Database Syst Rev, 2024 · checked 2026-10-06 · we read the abstract
4. ev-irana-04 · Observational data · systematic review and meta-analysis · n = 8829
   The pooled effect size for Hb improvement was 2.01 gm/dL (95% CI: 1.48-2.54, p < 0.001).
   
   Who: children and adolescents up to 19 years with ferritin-confirmed iron-deficiency anemia, at least 30 days of iron, 16 countries
   Effect: pooled hemoglobin rise 2.01 g/dL (95% CI 1.48-2.54); under 3 months 2.39 g/dL (0.72-4.07); 3-6 months 1.58 g/dL (0.93-2.23)
   Certainty: Studies 2013-2024 only; the abstract does not say the included studies were randomized; comparators placebo, no treatment or other regimens; pooled as standardized effect sizes, so the g/dL figure is approximate.
   PLoS One, 2025 · checked 2026-10-06 · we read the abstract
5. ev-irana-05 · Meta-analysis or systematic review · systematic review and meta-analysis of randomized trials · n = 11771
   Compared with oral iron, IV iron therapy was associated with higher mean levels of maternal hemoglobin (WMD in 15 studies, 0.59 g/dL [95% CI, 0.31-0.87 g/dL])
   
   Who: pregnant women with iron-deficiency anemia, randomized trials of intravenous vs oral iron
   Effect: hemoglobin at delivery WMD 0.59 g/dL (95% CI 0.31-0.87; 15 studies); transfusion RR 0.63 (0.49-0.82; 14 studies); mild adverse effects RR 0.56 (0.41-0.76)
   Certainty: One trial from the earlier version was retracted and removed; benefit largest when starting hemoglobin was 9 g/dL or lower.
   JAMA Netw Open, 2026 · checked 2026-10-06 · we read the abstract
6. ev-irana-06 · Meta-analysis or systematic review · systematic review and meta-analysis of randomized trials · n = 6831
   Ferrous sulfate supplementation significantly increased risk of GI side-effects versus placebo with an odds ratio (OR) of 2.32 [95% CI 1.74-3.08, p<0.0001, I2 = 53.6%]
   
   Who: adults in randomized trials of ferrous sulfate vs placebo or intravenous iron
   Effect: GI side effects OR 2.32 vs placebo (95% CI 1.74-3.08); OR 3.05 vs intravenous iron (2.07-4.48); no clear link with dose
   Certainty: Odds ratio, not risk ratio; moderate heterogeneity (I2 about 54%).
   PLoS One, 2015 · checked 2026-10-06 · we read the abstract
7. ev-irana-07 · Meta-analysis or systematic review · systematic review and meta-analysis of randomized trials · n = 1014
   The pooled analysis found a small, statistically non-significant increase in hemoglobin with daily dosing over alternate-day (MD: 0.28, 95% CI: -0.01 to 0.56, p = 0.06, z = 1.91).
   
   Who: people with iron-deficiency anemia in randomized trials of daily vs alternate-day oral iron
   Effect: hemoglobin MD 0.28 g/dL in favor of daily (95% CI -0.01 to 0.56); adverse effects RR 1.07 (0.86-1.34); metallic taste more frequent with daily
   Certainty: Very low certainty for most outcomes because of heterogeneity and imprecision.
   BMC Pharmacol Toxicol, 2025 · checked 2026-10-06 · we read the abstract
8. ev-irana-08 · Randomized controlled trial(s) · randomized controlled trial · n = 88
   At 6 weeks, the daily iron group had a mean increase in Hb of 0.8 ± 0.9 g/dL, whereas the alternate-day iron group had a mean increase of 0.5 ± 1.0 g/dL
   
   Who: 88 pregnant women, hemoglobin under 11.0 g/dL and ferritin 25 ug/L or less, 12 to 34 weeks
   Effect: hemoglobin rise 0.8 vs 0.5 g/dL at 6 weeks, adjusted difference -0.3 g/dL (95% CI -0.7 to 0.1); side effects similar
   Certainty: Small trial, unbalanced parity between arms; 98% had mild anemia.
   Am J Perinatol, 2025 · checked 2026-10-06 · we read the abstract
9. ev-irana-09 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of randomized trials · n = 33785
   In areas without services, iron (with or without folic acid) may increase clinical malaria slightly (RR 1.15, 95% CI 1.02 to 1.30; 7 trials, 19,754 children; low-certainty evidence).
   
   Who: children under 18 in hyperendemic or holoendemic malaria areas, oral iron with or without folic acid, 40 trials
   Effect: clinical malaria RR 0.93 (95% CI 0.87-1.00; high certainty); without malaria services RR 1.15 (1.02-1.30; 7 trials, 19,754 children; low certainty)
   Certainty: Low certainty for the subgroup; relevant only where malaria is intense and prevention is absent.
   Cochrane Database Syst Rev, 2026 · checked 2026-10-06 · we read the abstract
10. ev-irana-10 · Position of an expert body · agency fact sheet · n = —
    The Tolerable Upper Intake Level for iron is 45 mg for adults, and it ranges from 40 mg to 45 mg for infants, children, and adolescents, depending on age.
    
    Who: General population, NIH Office of Dietary Supplements iron fact sheet
    Effect: UL 45 mg/day adults, 40-45 mg/day for infants, children and adolescents; acute intakes above 20 mg/kg can cause intestinal necrosis
    Certainty: UL is set on gastrointestinal effects of iron salts; treatment doses above it are given under medical supervision.
    NIH Office of Dietary Supplements, Iron fact sheet for health professionals · checked 2026-10-06 · we read the section
11. ev-irana-11 · Position of an expert body · agency fact sheet · n = —
    Iron supplements may interact with medications, including levodopa and levothyroxine. In addition, proton pump inhibitors can potentially reduce iron absorption.
    
    Who: General population, NIH Office of Dietary Supplements iron fact sheet
    Effect: interactions: levodopa, levothyroxine; reduced absorption with proton pump inhibitors
    Certainty: Agency summary without interaction sizes.
    NIH Office of Dietary Supplements, Iron fact sheet for health professionals · checked 2026-10-06 · we read the section
12. ev-irana-12 · Position of an expert body · agency fact sheet · n = —
    The American College of Obstetricians and Gynecologists (ACOG) recommends low-dose iron supplementation (dose not specified) starting in the first trimester to decrease the prevalence of maternal anemia at delivery [68].
    
    Who: pregnant women, NIH Office of Dietary Supplements summary of ACOG and USPSTF positions
    Effect: ACOG: screen and give low-dose iron; USPSTF: insufficient evidence for routine screening and supplementation in asymptomatic women
    Certainty: Disagreement is about routine use in women without anemia; both agree established iron-deficiency anemia should be treated.
    NIH Office of Dietary Supplements, Iron fact sheet for health professionals · checked 2026-10-06 · we read the section