Iron Supplements vs Infusion: Which is Better?


An iron deficiency can cause significant side effects like fatigue, headaches, and more.

While the long-term solution is to simply incorporate more iron-rich foods in your diet, that takes a long time to correct a deficiency.

Instead, doctors will typically prescribe either iron supplements or an iron IV infusion, depending on the severity and individual patient preferences.

Is An Iron Infusion Better Than Supplements?

If a doctor wants to be really confident about correcting an iron deficiency, they will usually give an iron infusion.

One study compared the effectiveness of 2 types of IV iron infusions with an iron supplement. They found that (1):

The mean ferritin level differences were significantly higher at 4 weeks in the FCM (injection) vs oral iron group…

Ferritin is a reliable marker for iron levels, and both IV groups had similar levels.

In this case, ferritin levels were 166 µg/L in the first injection group, compared to 145 µg/L in the supplement group.

A similar difference in hemoglobin levels is shown in the graph below.

effect of oral iron supplements vs IV injections

One important note is that the total cost of treatment was similar in each group. This will obviously depend on the healthcare in your area though.

Another randomized, controlled trial compared an IV to oral iron in anemic patients (2). Injections were given once every 14 days, while supplements were taken 3 times per day for 56 days.

Again, the IV group had better outcomes:

The proportion of patients achieving the primary outcome (Hb increase ≥1 g/dL) was greater in the IV iron treatment group than in the oral iron treatment group (44.3% vs. 28.0%).

Clearly oral supplements did work for some people, and it’s not an all-or-nothing result (i.e. increasing iron levels by less than the goal is still progress), but IV injections were better.

One important note: These studies used the lowest quality oral iron supplements. For example, they used ferrous sulfate in the first study. Other forms of iron that are becoming more popular in commercial iron supplements like chelated iron and carbonyl iron absorb more easily and produce fewer side effects.

Unfortunately I haven’t come across a study comparing IV injections to either of those forms, but the results may be much closer.


Current research suggests that IV iron injections are more effective on average than oral supplements to increase iron levels.

Iron Infusion vs Supplements: Side Effects and Convenience

In reality, patients that go with iron supplements may experience better or worse results than the ones we saw in the study results above.

This has to do with 2 main factors that affect the outcome of treatment. Let’s look at them one at a time.

Side Effects of Iron Supplements

Iron infusions used to contain high-molecular-weight iron, which caused frequent adverse effects.

However, modern iron infusions use forms of low-molecular-weight iron, which rarely produce side effects. 

A systematic review found that IV injections of iron produce significantly fewer side effects than oral supplements (3).

If you’re curious, I’ve gone into much greater detail on why oral iron supplements often cause:

The reason that this is so important is because if someone experiences side effects, they are much less likely to follow the treatment, or at least follow it as they are supposed to (4).

This of course affects the result.


One reason that IV injections are often more effective in real life is because they are less likely to cause side effects than oral supplements, so patients continue with the full treatment course.

Convenience of Injections vs Supplements

How convenient a treatment method is will also affect the compliance of a patient, and the best treatment is one that a patient will actually follow through with.

There’s no clear “winner” here, as some people prefer supplements, and some prefer injections.

On one hand, injections are less frequent, usually once every few weeks or even months. However, many people don’t like needles, and getting to a physician’s office may not be convenient.

Supplements can be convenient since you can order or buy them easily over the counter. And while you should consult a doctor to confirm an iron deficiency, that’s not always possible, and iron supplements can be a useful solution. However, taking multiple supplements per day is inconvenient, and some people have trouble swallowing pills (although liquid forms are available).

So it really comes down to the individual.


Before prescribing either iron supplements or an infusion, a doctor must weigh personal preferences and the potential for side effects to maximize the results of the chosen treatment.

Neither Iron Supplements or Infusions are Long-Term Solution

Iron deficiency anemia is quite common, but it’s important to recognize that supplements or infusions are not a good long-term solution in the majority of cases.

Instead, it’s important to try to include more iron-rich foods in your diet, especially if you’re on a plant-based diet where getting iron can be more difficult. That will let you maintain healthy iron levels, leading to higher energy levels.

One of the dangers of iron supplements or injections is that iron levels can actually get too high and cause chronic inflammation. This can raise the risk of several diseases like cancer and heart disease.

Again, that’s why iron supplementation in any form should be done under the guidance of a medical professional whenever possible.

About the author

Dale Cudmore

Your friendly neighborhood vegan from Toronto. Chemical engineer turned semi-professional soccer player and freelance nutrition writer. I've been vegan for years and try to make life easier for others by sharing what I've learned.