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RankingsWhich iron and B12 supplement is best?
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If a blood test shows you are low in both iron and vitamin B12, you are not alone. Both nutrients are essential for making healthy red blood cells, and a shortfall in either one can leave you feeling exhausted, foggy and short of breath. But they do different jobs inside the same process, which is why a supplement that covers both can make practical sense.
The catch is that most iron supplements contain no B12 at all, and most B12 supplements contain no iron. Only a handful of formulas combine the two in meaningful doses, and the quality varies. Some deliver a generous hit of methylcobalamin alongside well-absorbed iron bisglycinate; others add a token trace of cyanocobalamin that barely meets the RDA.
We compared six supplements that provide both iron and B12 in a single product. We scored each one on dose and absorption, stomach tolerance, value and verified buyer feedback. Below, we explain why these two nutrients work as a pair, who is most likely to need both, and which formula came out on top.
The best iron and B12 supplement for most people is Thorne Ferrasorb, which pairs 36 mg of iron bisglycinate with 300 mcg of methylcobalamin B12 plus active folate and cofactors.
Our top pick is Thorne – Ferrasorb. It combines a well-absorbed iron form with a generous B12 dose and the cofactors that support red blood cell production. If you want a clinically studied alternative, MegaFood – Blood Builder is a strong second choice.
Why your body needs iron and B12 together
Iron and vitamin B12 are often discussed separately, but they work on two different steps of the same production line: making red blood cells. Iron is the raw material your bone marrow uses to build hemoglobin, the protein that carries oxygen in each red blood cell. Without enough iron, your body produces smaller, paler cells that carry less oxygen.
Vitamin B12 plays a different role. It is needed for DNA synthesis inside the bone marrow, which is how new red blood cells are assembled and matured. Without enough B12, the marrow produces fewer cells, and the ones it does make tend to be abnormally large and fragile. The NIH Office of Dietary Supplements notes that B12 deficiency can cause tiredness, weakness, numbness and even neurological damage if left untreated.
In short, iron supplies the cargo (hemoglobin) and B12 helps build the vehicle (the red blood cell itself). A shortage of either nutrient can cause anemia, but the type is different: iron deficiency typically produces microcytic (small-cell) anemia, while B12 deficiency produces megaloblastic (large-cell) anemia. When both are low at the same time, the opposing effects on cell size can mask each other, making a routine blood count look deceptively normal even though you are deficient in both.
When iron and B12 are both low, small iron-deficient cells and large B12-deficient cells can average out to a normal-looking MCV on a blood test. This "dual deficiency" pattern is well documented in clinical research and can delay diagnosis. If you have symptoms of anemia but your MCV is normal, ask your doctor to check both ferritin and B12 levels separately.
Who is most likely to need both iron and B12
Vegans and vegetarians
Red meat is the richest dietary source of both iron and B12. People who avoid it entirely are at higher risk of falling short on both nutrients. The NIH lists vegetarians and vegans among the groups most likely to develop B12 deficiency, and plant-based iron (non-heme) is absorbed less efficiently than the heme iron found in meat.
Adults over 50
Stomach acid production tends to decline with age, and stomach acid is needed to release B12 from food. The NIH recommends that adults over 50 get most of their B12 from supplements or fortified foods for this reason. Lower acid also reduces iron absorption, making a combined supplement a practical choice for older adults.
People with heavy periods
Heavy menstrual bleeding is the most common cause of iron deficiency in premenopausal women. If their diet is also low in B12, as it can be with restricted eating patterns, both levels may drop. A supplement that covers both nutrients saves taking two separate pills.
Post-bariatric surgery
Gastric bypass and similar procedures reduce the area of gut available to absorb nutrients. Both iron and B12 absorption can be significantly impaired, and lifelong supplementation of both is often recommended after surgery.
How we scored these six supplements
We evaluated 14 iron supplements that also contain B12, then narrowed the list to six that are widely available in the US and provide both nutrients in doses worth taking. We scored each product on four criteria, weighted by importance, and linked to our full methodology at how we rank products.
Dose and absorption (35%) looked at the iron form (bisglycinate is better absorbed and gentler than ferrous sulfate or fumarate), the elemental iron dose relative to the 18 mg RDA for adult women, the B12 form (methylcobalamin is the active form; cyanocobalamin needs converting), the B12 dose relative to the 2.4 mcg RDA, and whether cofactors like vitamin C, folate and B6 are included.
Tolerance (25%) considered the iron form (bisglycinate and liquid forms cause fewer GI side effects), whether the product is known to cause constipation or nausea, and whether clinical data or large buyer-review datasets support the tolerance claims.
Value (20%) compared the cost per day at full retail, factoring in pack size and daily dose. We did not publish prices because they change frequently.
Buyer feedback (20%) drew on verified reviews from Amazon, iHerb, Walmart and retailer sites. We looked at overall ratings, common praise, recurring complaints and whether reviewers reported measurable outcomes (ferritin improvement, energy changes).
Rank Product Iron & B12 per dose Score #1Best overall Thorne - Ferrasorb Iron bisglycinate capsule
36 mg iron + 300 mcg B12 (methylcobalamin)8.8/10 Check price #2Best clinically studied MegaFood - Blood Builder Ferrous bisglycinate tablet
26 mg iron + 30 mcg B12 (cyanocobalamin)8.7/10 Check price #3Best budget pick Nature's Bounty - Gentle Iron Ferrous bisglycinate capsule
28 mg iron + 8 mcg B12 (cyanocobalamin)8.5/10 Check price #4Best for B12 dose Garden of Life - Vitamin Code Raw Iron Brown rice chelate capsule
22 mg iron + 500 mcg B12 (methylcobalamin)8.2/10 Check price #5Best food-based New Chapter - Fermented Iron Complex Fermented ferrous fumarate tablet
9 mg iron + 30 mcg B12 (cyanocobalamin)7.8/10 Check price #6Best liquid Floradix - Iron + Herbs Ferrous gluconate liquid
10 mg iron + 6.8 mcg B12 (cyanocobalamin)7.5/10 Check price
Six iron and B12 supplements, compared
Thorne - Ferrasorb
The most complete iron-plus-B12 formula we found: well-absorbed bisglycinate iron with a generous methylcobalamin B12 dose and full cofactor support.
- Elemental iron36 mg (iron bisglycinate)
- Vitamin B12300 mcg (methylcobalamin)
- Folate667 mcg DFE (L-5-MTHF)
- Vitamin C15 mg
- Vitamin B65 mg
- you want a high-dose iron with meaningful B12 in one capsule
- you prefer methylcobalamin over cyanocobalamin
- you want active folate rather than folic acid
- you need a lower iron dose (under 18 mg)
- you are looking for the cheapest option
Thorne Ferrasorb stands out because it was designed specifically as an iron-with-cofactors formula. The 36 mg of iron bisglycinate (Albion Ferrochel) is paired with 300 mcg of methylcobalamin B12, the bioactive form that does not need converting. It also includes L-5-MTHF (active folate), vitamin B6 and 15 mg of vitamin C to support absorption. That cofactor lineup makes it one of the few supplements that covers every nutrient involved in red blood cell production.
Verified buyers on retailer sites consistently report good stomach tolerance and measurable ferritin improvement. “Helped me get my ferritin levels up pretty quickly” (Nashima G., NHC). Another reviewer noted it “didn’t bother his stomach or digestion” (Lynn R., NHC). The main trade-off is price: Thorne is a premium brand, and 60 capsules at two per day means a 30-day supply.
Where to buy
Prices change often, so we don't show them here: check the retailer for today's price.
MegaFood - Blood Builder
The only iron supplement in this list backed by a published clinical study showing it raises iron levels without common side effects.
- Elemental iron26 mg (ferrous bisglycinate, FoodState)
- Vitamin B1230 mcg (cyanocobalamin)
- Folate680 mcg DFE (folic acid)
- Vitamin C15 mg
- Beet root125 mg
- you want a clinically studied formula
- you prefer a whole-food-based supplement
- you value a proven track record on tolerance
- you want a higher B12 dose or methylcobalamin form
- you need a capsule rather than a tablet
MegaFood Blood Builder has something most iron supplements lack: clinical data. A published study found that it raised iron levels without causing the nausea or constipation typically associated with iron supplements. The FoodState process pairs iron with whole-food cofactors including beet root, which supplies naturally occurring nitrates. The 26 mg iron dose sits above the RDA and below prescription-strength levels, making it a solid maintenance dose.
The B12 content is modest at 30 mcg of cyanocobalamin, which is over 1,000% of the 2.4 mcg RDA but far less than Thorne's 300 mcg methylcobalamin. For most people without a B12 absorption issue, 30 mcg is adequate. Buyers are enthusiastic: "My iron levels are now in the normal range" (Carebear, well.ca). Several reviewers highlight the absence of stomach problems: "It doesn't cause any stomach upset, and provides a great lift in iron" (Jrattink, well.ca).
Where to buy
Prices change often, so we don't show them here: check the retailer for today's price.
Nature's Bounty - Gentle Iron
A 90-count bottle of bisglycinate iron with B12, folate and vitamin C at a price that undercuts most competitors.
- Elemental iron28 mg (ferrous bisglycinate)
- Vitamin B128 mcg (cyanocobalamin)
- Folate667 mcg DFE (folic acid)
- Vitamin C60 mg
- you want a gentle iron at a low daily cost
- you need a three-month supply in one bottle
- you want a straightforward formula without extras
- you need a meaningful B12 dose (8 mcg is just above the RDA)
- you prefer methylcobalamin or active folate
Nature's Bounty Gentle Iron is the value pick in this list. At 90 capsules per bottle with a one-a-day dose, it offers a full three-month supply. The 28 mg of ferrous bisglycinate is a sensible daily dose, and the 60 mg of vitamin C is the highest in this group, which supports iron absorption. The formula also includes 667 mcg DFE of folic acid, a useful addition for women of childbearing age.
The weak point is the B12 dose: just 8 mcg of cyanocobalamin. That is roughly 333% of the 2.4 mcg RDA, so it technically covers your daily need, but it is far less than what Thorne or Garden of Life provide. If you are already getting some B12 from your diet and mainly need iron, this is a smart choice. Buyers on Walmart praise the stomach tolerance: "Regular iron supplements are often hard on my stomach. These supplements are not" (Shoppers, Walmart).
Garden of Life - Vitamin Code Raw Iron
The highest B12 dose in this group (500 mcg methylcobalamin) with added probiotics, but only 30 capsules per bottle.
- Elemental iron22 mg (brown rice chelate)
- Vitamin B12500 mcg (methylcobalamin)
- Folate400 mcg DFE
- Vitamin C25 mg
- Probiotics500 million CFU
- you want the highest B12 dose in one iron supplement
- you prefer methylcobalamin and whole-food nutrients
- you want added probiotics for digestive comfort
- you want proven iron absorption data (brown rice chelate is less studied than bisglycinate)
- you need more than a 30-day supply per bottle
Garden of Life Vitamin Code Raw Iron delivers the highest B12 dose in this roundup: 500 mcg of methylcobalamin. That is over 20,000% of the RDA, which may be useful if you have a known B12 absorption issue. The iron comes from a brown rice chelate at 22 mg, paired with 25 mg of vitamin C and 500 million CFU of probiotics. The whole-food approach means the nutrients are cultured with fruits and vegetables.
The main drawback is the iron form. Brown rice chelate is less studied than Albion Ferrochel bisglycinate, and there is limited independent data on its absorption rate. The bottle also contains just 30 capsules, making it a one-month supply at a relatively high cost per day. The capsules are large, which some buyers find difficult to swallow. Garage Gym Reviews notes that some customers still report constipation and GI issues despite the "non-constipating" marketing claim.
Where to buy
Prices change often, so we don't show them here: check the retailer for today's price.
New Chapter - Fermented Iron Complex
A fermented, food-based iron tablet that is gentle on the stomach, but the 9 mg iron dose is well below the RDA for most women.
- Elemental iron9 mg (fermented ferrous fumarate)
- Vitamin B1230 mcg (cyanocobalamin)
- Folate1,333 mcg DFE (folic acid)
- Vitamin C30 mg
- Zinc5 mg
- you want a whole-food, fermented supplement
- you have a sensitive stomach and prefer a low iron dose
- you want added zinc and generous folate
- you need to correct an iron deficiency (9 mg is unlikely to be enough)
- you want the most efficient iron form per milligram
New Chapter takes a food-first approach, fermenting its iron with probiotics and organic vegetables. The fermentation process is designed to make the iron gentler on the stomach, and buyer reviews on iHerb support this: "No stomach upset or constipation like many other iron products" (iHerb customer). The formula also includes a generous 1,333 mcg DFE of folate and 5 mg of zinc, making it one of the more complete formulas in this group.
The significant limitation is the iron dose: just 9 mg. The RDA for adult women aged 19 to 50 is 18 mg, and the RDA for men and postmenopausal women is 8 mg. So this supplement meets the male RDA but falls well short for premenopausal women, who are the group most likely to need iron. The B12 is 30 mcg of cyanocobalamin, which is adequate but not exceptional. Best suited to people who want a maintenance dose rather than a deficiency-correcting one.
Where to buy
Prices change often, so we don't show them here: check the retailer for today's price.
Floradix - Iron + Herbs
A liquid iron formula with herbal extracts and B vitamins, ideal if you cannot swallow capsules, but the B12 dose is minimal.
- Elemental iron10 mg per 10 mL (ferrous gluconate)
- Vitamin B126.8 mcg (cyanocobalamin)
- Also containsvitamins B1, B2, B6
- Herbal extractsnettle, rosehip, carrot, spinach
- you cannot swallow pills or capsules
- you want a liquid formula with herbal extracts
- you prefer a low-dose, gentle daily iron
- you need a meaningful B12 dose (6.8 mcg is the lowest in this list)
- you want a shelf-stable supplement (Floradix must be refrigerated after opening)
Floradix is the only liquid option in this roundup, which makes it the obvious choice if you struggle with pills. The ferrous gluconate iron is suspended in a blend of herbal extracts (nettle, rosehip, fennel) and fruit juices, and the taste is generally well tolerated. At 10 mg per serving, the iron dose is modest, and Floradix also provides B1, B2 and B6 alongside the iron.
The B12 content is the weakest in the group at 6.8 mcg of cyanocobalamin. That covers roughly 283% of the 2.4 mcg RDA, so it meets the minimum, but anyone with a B12 absorption issue would need a separate supplement. Floradix also requires refrigeration after opening and should be used within four weeks, which adds a practical inconvenience. It contains no preservatives, which some buyers see as a plus, but it means the product does not travel well.
Where to buy
Prices change often, so we don't show them here: check the retailer for today's price.
Who should not take iron without medical advice
Iron is one of the few supplements that can cause serious harm if taken unnecessarily. Unlike water-soluble vitamins, excess iron accumulates in the body and can damage organs. You should speak with your doctor before taking an iron supplement if any of the following apply to you.
Talk to your doctor before taking iron ifYou have not had a blood test confirming iron deficiency. You have hemochromatosis or a family history of iron overload. You are taking medication for thyroid conditions, antibiotics (tetracycline, quinolones) or antacids. You are pregnant or breastfeeding (your doctor or midwife should advise on dose). You have a condition affecting iron absorption, such as celiac disease or inflammatory bowel disease. Always keep iron supplements out of reach of children: accidental overdose is a leading cause of poisoning in young children.
Iron can also reduce the absorption of certain medications, including levothyroxine, levodopa and some antibiotics. If you take any of these, your doctor may advise spacing your iron dose at least two hours apart from your medication.
Take iron on an empty stomach with a source of vitamin C (a glass of orange juice, a kiwi, or the vitamin C already in your supplement) for best absorption. Avoid taking it with tea, coffee, dairy or calcium supplements, which can reduce how much iron your body absorbs.
Frequently asked questions
Can I take iron and B12 at the same time?
Yes. There is no known absorption conflict between iron and vitamin B12 when taken together. They support different steps of red blood cell production: iron is used to build hemoglobin, while B12 is needed for DNA synthesis and cell maturation. Many supplements combine both in a single dose.
How long does it take for iron and B12 supplements to work?
Iron stores (ferritin) typically begin to rise within 2 to 4 weeks of starting supplementation, and hemoglobin levels usually improve within 6 to 8 weeks. B12 levels can improve within days to weeks, but neurological symptoms may take several months to resolve. Your doctor can confirm progress with a follow-up blood test.
Is methylcobalamin better than cyanocobalamin?
Methylcobalamin is the bioactive form of B12, meaning your body can use it directly without conversion. Cyanocobalamin is synthetic and must be converted, but it is well studied, stable and effective for most people. People with the MTHFR gene variant may benefit from methylcobalamin, but both forms are considered effective by the NIH.
Do I need a prescription for iron and B12 supplements?
In the US, iron and B12 supplements are available over the counter. However, it is important to confirm a deficiency with a blood test before starting iron, because excess iron can accumulate and cause harm. B12 supplements are generally safe even at high doses, as the body excretes what it does not need.
Can iron and B12 deficiency occur at the same time?
Yes. Dual deficiency is common in vegans and vegetarians, older adults with reduced stomach acid, people who have had bariatric surgery, and those with malabsorption conditions. When both are low simultaneously, the MCV (mean cell volume) on a blood test can appear normal because the opposing effects on cell size cancel each other out, which can delay diagnosis.
The bottom line
If you need both iron and B12 in a single supplement, Thorne Ferrasorb is the most complete option we found. It pairs a well-absorbed iron bisglycinate with a generous 300 mcg of methylcobalamin B12, active folate and vitamin C, covering the full set of cofactors your body needs to build healthy red blood cells. Buyers consistently report good tolerance and measurable improvements in ferritin levels.
For a clinically studied alternative, MegaFood Blood Builder has published data showing it raises iron levels without the usual side effects. And if budget is your priority, Nature’s Bounty Gentle Iron offers a 90-day supply of bisglycinate iron at a fraction of the cost, though its B12 dose is minimal.
Whichever you choose, get a blood test first. Iron is not a supplement to take on a guess, and knowing your ferritin and B12 levels will help you and your doctor pick the right dose.
Thorne - Ferrasorb
- 36 mg iron bisglycinate (Ferrochel)
- 300 mcg methylcobalamin B12
- Active folate (L-5-MTHF) plus vitamin C and B6
- Strong buyer reviews for tolerance and ferritin improvement
Independent guides to natural remedies and supplements, checked against NHS and EFSA references.