Quick answer

Ask your pharmacist or doctor before combining. Official sources document four supplements for proton pump inhibitors such as omeprazole: vitamin B12, B complex, magnesium and iron. Here the medicine lowers the nutrient, not the other way around: the omeprazole label cites poor B12 absorption after more than 3 years and rare low magnesium.^1,2,3

Key facts

The omeprazole label says daily use of an acid-suppressing medicine for a long time, such as more than 3 years, may lead to poor absorption of vitamin B12.¹
Low blood magnesium has been reported rarely after at least 3 months of use, mostly after a year, and doctors may check magnesium before and during long-term use.²
NIH lists proton pump inhibitors among the medicines iron can interact with.⁴
MedlinePlus names iron supplements and St. John's wort as nonprescription or herbal products that may interact with omeprazole.³

What do proton pump inhibitors do, and why do nutrients come up?

Proton pump inhibitors reduce stomach acid. MedlinePlus, using omeprazole as its example, says prescription omeprazole is used for acid reflux and the damage it can cause to the esophagus, for conditions in which the stomach makes too much acid, and for ulcers in the stomach or intestine.³

Stomach acid does more than digest food, and that is the thread through this page. The omeprazole label links long-term acid suppression to poor absorption of vitamin B12, and NIH says the acid matters for absorbing nonheme iron. In these four entries the direction is mostly the medicine lowering a nutrient, not a supplement misbehaving with the medicine.^1,5

Do proton pump inhibitors lower vitamin B12?

Your doctor may want to check on you

Proton pump inhibitors such as omeprazole and lansoprazole reduce stomach acid, which the body needs to release B12 from food. The omeprazole label says daily use of any acid-suppressing medicine for a long time, such as more than 3 years, may lead to poor absorption of B12.^1,6,7

On the medicine's label

NIH explains that stomach acid frees B12 from the protein it is attached to in food, and that B12 in supplements is not attached to protein and does not need that first step. The label's wording is about long daily use, so a person who has taken one of these medicines for years has a different question from someone on a short course. Ask your pharmacist whether B12 should be checked.^1,6,7

Your doctor may want to check on you

Daily use of acid-reducing medicines such as omeprazole over a long time, for example more than 3 years, can reduce how much vitamin B12 the body absorbs from food. The omeprazole label notes rare reports of B12 deficiency.^8,9

On the medicine's label

The B complex entry is the same concern seen through a different product, since B complex supplements usually contain B12. NIH puts the usual B12 amount in a B complex at 50 to 500 mcg and notes that the share absorbed falls as the amount rises.⁹

Can a proton pump inhibitor cause low magnesium?

Your doctor may want to check on you

Proton pump inhibitors such as omeprazole and esomeprazole can cause low blood magnesium when taken for a long time, usually more than a year. The omeprazole label says this has been reported rarely after at least three months and that doctors may check magnesium before and during long-term use.^2,10,11

On the medicine's label

This one concerns a blood level, not a supplement problem. In the reported cases, most people needed magnesium replacement and had to stop the medicine. MedlinePlus also asks people to tell their doctor if they have ever had low magnesium, calcium or potassium. Whether a magnesium supplement belongs in that picture is a question for the prescriber.^2,3

Does a proton pump inhibitor change how iron supplements work?

Two official pages name this pair. NIH's iron fact sheets list proton pump inhibitors among the medicines iron can interact with, and MedlinePlus names iron supplements as a nonprescription product that may interact with omeprazole.^3,4,5

Your doctor may want to check on you

Proton pump inhibitors such as omeprazole and lansoprazole lower stomach acid, which can reduce how much nonheme iron is absorbed. Years of use did not deplete iron in people whose stores were normal, but people with low iron who take these medicines may respond less well to iron supplements.^4,5

Reported in studies

Iron appears on the levothyroxine page too, for a different reason: there it binds the tablet, while here it is the acid-lowering medicine that changes how iron is absorbed.¹²

What about calcium, zinc or other supplements with a proton pump inhibitor?

MedlinePlus's omeprazole page names two nonprescription or herbal products that may interact: iron supplements and St. John's wort. It also asks people to tell their doctor about low vitamin B12 and about thin, weak bones.³

The sources checked do not address calcium, zinc or other supplements. That is not a finding either way, so ask your pharmacist.

Why does every entry say 'monitor' instead of 'avoid'?

The four proton pump inhibitor entries, with how each is known^1,2,5
Supplement	What the entry describes	How it is known	Label shown
Vitamin B12	Long daily use may lead to poor absorption from food	On the medicine's label	Your doctor may want to check on you
B complex	The same B12 concern, in a combined product	On the medicine's label	Your doctor may want to check on you
Magnesium	Rare low blood magnesium after months or years of use	On the medicine's label	Your doctor may want to check on you
Iron	Less nonheme iron absorbed, with no depletion in people whose stores were normal	Reported in studies	Your doctor may want to check on you

Monitor means a doctor may want to check on you. It is not an instruction to avoid a supplement. Three of the entries rest on the omeprazole label and one on studies, and none is merely expected.

What to ask your pharmacist if you take a proton pump inhibitor

How long have I taken this medicine, and does that change whether my B12 or magnesium should be checked?
Do any of my supplements contain B12, iron or magnesium?
Is the heartburn product I use a proton pump inhibitor or a different kind of acid reducer?³
Do I take iron or St. John's wort, which MedlinePlus names for omeprazole?³

Questions people ask

What supplements should you avoid with proton pump inhibitors?

The sources checked do not tell people to avoid a supplement. They document four entries, vitamin B12, B complex, magnesium and iron, mostly because the medicine can lower them. MedlinePlus also names iron supplements and St. John's wort as products that may interact with omeprazole.^1,2,3

What vitamins should you not take with proton pump inhibitors?

The vitamin entries are vitamin B12 and B complex. The concern is the medicine lowering how much B12 the body absorbs from food after long daily use, so ask your pharmacist whether to have B12 checked.^1,8

Which supplements interact with proton pump inhibitors?

NIH and the omeprazole label document B12, magnesium and iron, and MedlinePlus names iron supplements and St. John's wort for omeprazole. The sources checked do not address other supplements, which is not a finding either way, so ask your pharmacist.^2,3,7

Can omeprazole cause low vitamin B12?

The omeprazole label says daily use of any acid-suppressing medicine for a long time, such as more than 3 years, may lead to poor absorption of vitamin B12. Ask your doctor whether a blood test is right for you.¹

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This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.