Iron deficiency is the most common nutrient deficiency worldwide, affecting 20% of women of childbearing age. GLP-1 users with reduced food intake are at higher risk. This guide covers when to supplement and which to choose.
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Why iron matters on GLP-1s
Iron is essential for:
- Hemoglobin production — carries oxygen in blood
- Energy production — deficiency causes fatigue
- Immune function — white blood cells need iron
- Cognitive function — brain needs oxygen
- Hair health — deficiency contributes to hair loss
- Skin health — deficiency causes pallor
GLP-1 users at higher risk because:
- Reduced food intake (especially meat)
- Reduced calorie intake overall
- Some users shift to plant-based eating (iron from plants is less bioavailable)
- Rapid weight loss can affect iron status
Who needs iron supplementation
Definitely supplement if:
- Bloodwork shows iron deficiency (low ferritin, low hemoglobin)
- You're a menstruating woman with heavy periods
- You're pregnant or planning pregnancy
- You have diagnosed anemia
- You have celiac disease or other malabsorption issues
Probably don't supplement if:
- You're a man (unless bloodwork shows deficiency)
- You're postmenopausal (unless deficient)
- You have hemochromatosis (iron overload disorder)
- Your bloodwork shows normal or high iron
Get tested first
Iron supplementation without deficiency is harmful. Get bloodwork (ferritin, hemoglobin, iron panel) before starting. See our lab tests guide.
Forms of iron
Ferrous sulfate (most common)
Standard form, well-absorbed, inexpensive. Can cause GI upset (constipation, nausea). 65mg elemental iron per 325mg tablet.
Ferrous bisglycinate (gentler)
Better tolerated than sulfate. Less GI upset. Slightly more expensive. Good for sensitive users.
Ferrous gluconate
Lower elemental iron per tablet (38mg per 325mg). Gentler than sulfate but need more tablets.
Heme iron
Derived from animal sources. Best absorbed. Most expensive. Limited availability.
Best form for GLP-1 users
Ferrous sulfate (Nature Made) for value and availability. Ferrous bisglycinate if you experience GI upset from sulfate.
Our top pick
Nature Made Iron 65mg (Ferrous Sulfate) — 180 Tablets
USP-verified iron for menstruating GLP-1 users with documented deficiency. Best taken with vitamin C; allow 2 hours between iron and other medications.
$10–14Check Price on Amazon
Why Nature Made Iron 65mg
- USP verified (third-party tested)
- 65mg elemental iron per tablet (325mg ferrous sulfate)
- 180-day supply per bottle
- Inexpensive
- Gluten-free
- Trusted brand
How to take iron
Timing
- Take on empty stomach for best absorption (but may cause nausea)
- If nausea occurs, take with small amount of food
- Take 2 hours apart from calcium, magnesium, antacids (reduce absorption)
- Take 2 hours apart from thyroid medications
Take with vitamin C
Vitamin C significantly improves iron absorption. Take iron with a glass of orange juice, or with vitamin C supplement, or with food high in vitamin C.
Avoid taking with
- Coffee or tea (tannins reduce absorption)
- Calcium supplements or dairy (calcium competes)
- Magnesium supplements
- Antacids
- High-fiber foods (phytates reduce absorption)
Side effects to expect
- Dark stools — normal, harmless
- Constipation — common; increase fluids and fiber
- Nausea — take with food if severe
- Stomach upset — usually improves over time
After 3 months of iron supplementation, get bloodwork rechecked. Iron levels should improve. If not, your provider may investigate absorption issues or other causes. Don't supplement indefinitely without monitoring.
FAQs
Should men take iron supplements?
Generally no, unless bloodwork shows deficiency. Men don't lose iron through menstruation and are at risk for iron overload. Get tested first.
Why does iron cause constipation?
Iron affects gut motility and gut microbiome. Increase fluids and fiber, take magnesium, or switch to ferrous bisglycinate (gentler form) if constipation is significant.