Compare Ferrous Sulfate with Iron Supplement Alternatives

If you’ve been told you’re low on iron, chances are your doctor reached for ferrous sulfate. It’s cheap, widely available, and has been the go-to for decades. But if you’ve tried it and ended up with stomach cramps, constipation, or just felt like it wasn’t working, you’re not alone. Many people struggle with ferrous sulfate - not because it doesn’t work, but because it’s hard on the body. The good news? There are better options out there, and they’re not just fancy marketing. Some work faster, cause fewer side effects, or are easier to stick with long-term.

Why Ferrous Sulfate Is Still Common

Ferrous sulfate is the most prescribed iron supplement in the UK and the US. It’s simple: it contains 20% elemental iron, which means a 325 mg tablet gives you about 65 mg of actual iron. That’s a lot. And because it’s been around since the 1950s, doctors know how to dose it, pharmacies stock it, and insurance covers it. It’s also dirt cheap - a month’s supply can cost under £5.

But here’s the catch: that high iron concentration is a double-edged sword. Your gut doesn’t absorb all of it. The excess sits in your intestines, irritating the lining. That’s why nausea, bloating, and constipation are so common. In fact, up to 70% of people taking ferrous sulfate report side effects, according to a 2023 review in the British Journal of Haematology. For some, it’s so bad they stop taking it - even if their iron levels haven’t improved.

Ferrous Fumarate: A Smoother Ride

Ferrous fumarate is the next most common iron salt after sulfate. It has a slightly lower percentage of elemental iron - about 33% - so a 300 mg tablet gives you roughly 100 mg of iron. Sounds like more? It’s not. The key difference is how your body handles it.

Studies show ferrous fumarate causes fewer gastrointestinal side effects than ferrous sulfate. One 2022 trial with 120 women diagnosed with iron-deficiency anemia found that 68% of those on fumarate reported no stomach issues, compared to only 39% on sulfate. That’s a big jump. Fumarate also seems to be absorbed a bit more efficiently, meaning less waste and less gut irritation.

It’s not magic. You can still get constipation. But if you’ve had a bad reaction to sulfate, fumarate is the first alternative to try. It’s just as affordable and available over the counter. Many UK pharmacies stock it under brands like Ferro-Folgamma or Fumarate Iron.

Ferrous Gluconate: Gentle but Slower

Ferrous gluconate has even less elemental iron - only about 12% per tablet. So a 325 mg tablet gives you just 39 mg of iron. That sounds weak, right? But here’s the twist: because it’s gentler, many people can take it without side effects, which means they actually stick with it.

Consistency beats intensity. If you take ferrous sulfate and skip doses because your stomach hurts, you’re not getting enough iron. If you take gluconate daily without issue, your levels will rise - just slower. In a 2021 study published in Clinical Nutrition, patients on gluconate showed the same improvement in hemoglobin after 12 weeks as those on sulfate, but with 50% fewer dropouts.

This makes gluconate ideal for people with sensitive stomachs, older adults, or anyone who’s had bad reactions before. It’s often found in combination with folic acid or vitamin B12, which helps if your anemia is tied to diet or pregnancy.

Iron Bisglycinate: The Premium Choice

If you’ve tried the others and still can’t tolerate iron, iron bisglycinate might be your answer. It’s not a sulfate, fumarate, or gluconate - it’s a chelated form. That means the iron is bound to glycine, an amino acid, making it easier for your body to absorb without irritating your gut.

Studies show iron bisglycinate has up to 90% absorption rates, compared to 15-35% for ferrous sulfate. That means you need less of it. A typical dose is 25-50 mg of elemental iron per day - less than half of what you’d take with sulfate. Side effects? Nearly nonexistent. In a 2023 meta-analysis of 11 trials, patients on bisglycinate reported 80% fewer gastrointestinal complaints than those on sulfate.

It’s more expensive - a month’s supply can cost £15-£25 - but many find it worth it. If you’ve given up on iron supplements because of side effects, bisglycinate could be your comeback. Brands like Thorne Iron Bisglycinate and Pure Encapsulations are available in the UK through online pharmacies or health stores.

Other Options: Heme Iron and IV Iron

Not all iron supplements are created equal. Heme iron polypeptide comes from animal sources - usually pork or beef. It’s absorbed differently than non-heme iron (the kind in pills), and doesn’t need stomach acid to work. That makes it great for people with low stomach acid, older adults, or those on acid-reducing meds like omeprazole.

One study found heme iron raised ferritin levels faster than ferrous sulfate in just 6 weeks. But it’s pricier, and not everyone wants to take a supplement made from meat. It’s also not widely available in the UK without a prescription.

Then there’s intravenous (IV) iron. If you’ve tried everything orally and your iron still won’t budge - maybe because you have Crohn’s disease, heavy periods, or kidney disease - IV iron bypasses your gut entirely. Options like ferric carboxymaltose (Ferinject) or iron sucrose (Venofer) are given in clinics. One infusion can replace months of pills. Side effects? Rare, but possible. You’ll need a specialist to manage this.

What to Consider When Choosing

Here’s a simple way to decide:

• Start with ferrous sulfate if you’re on a tight budget and have no history of stomach issues.
• Switch to ferrous fumarate if sulfate gave you nausea or constipation.
• Try ferrous gluconate if you need something gentle and can wait 3-4 months for results.
• Go for iron bisglycinate if you’ve tried everything else and still can’t tolerate iron.
• Ask about IV iron if your levels stay low despite months of oral supplements.

Also, take your iron on an empty stomach if you can - it absorbs better. But if that makes you sick, take it with a small amount of food. Avoid calcium, antacids, tea, or coffee within 2 hours - they block absorption.

And always get your levels checked again after 3 months. Iron isn’t something you take forever. Once your hemoglobin is back up, your doctor may switch you to a maintenance dose or stop it entirely.

Real Stories, Real Results

One woman in Chester, 42, had been taking ferrous sulfate for 8 months. Her iron was still low. She switched to bisglycinate. Within 6 weeks, her energy returned. No bloating. No constipation. She’s now been on it for 14 months and her ferritin is normal.

A man in Liverpool, 68, with acid reflux, couldn’t absorb any oral iron. His doctor gave him an IV infusion. Within 3 weeks, his fatigue vanished. He didn’t need pills again for a year.

These aren’t rare cases. They’re common outcomes when people stop forcing a supplement that doesn’t suit them.

Bottom Line

Ferrous sulfate isn’t broken - it just isn’t the right fit for everyone. The best iron supplement is the one you can take without pain, without skipping days, and without giving up. Whether it’s fumarate, gluconate, bisglycinate, or even IV iron, there’s an option that matches your body - not just your prescription pad.

Don’t suffer through side effects thinking it’s normal. Ask your doctor about alternatives. Your gut - and your energy - will thank you.