Supplements and Omeprazole.
Omeprazole, sold under the brand names Losec, Prilosec, is a proton pump inhibitor (PPI): it suppresses gastric acid production by inhibiting the H+/K+ ATPase pump.
Omeprazole is the most prescribed PPI in England at around 47 million items per year per NHSBSA, and the original drug of the class. Mechanism mirrors lansoprazole. Irreversible H+/K+ ATPase inhibition in gastric parietal cells, holding acid suppression for 12 to 24 hours per dose. Two omeprazole-specific points sit outside the class story. First, omeprazole inhibits CYP2C19 more strongly than lansoprazole, which matters for clopidogrel. Both the FDA and MHRA flag that omeprazole can reduce clopidogrel's antiplatelet effect by blocking its conversion to the active metabolite. Second, the same B12, magnesium, iron, and calcium absorption profile applies, but the heavier CYP2C19 footprint also touches some psychiatric medicines (diazepam, citalopram at higher doses). Annual blood work review on long-term PPI users is sensible. The alternative is the deprescribing pathway that NICE has been pushing since 2019.
Below are the 9 documented pairs we have explicitly assessed against Omeprazole in the Distil database: 8 amber and 1 green. The pairs cluster around 2 mechanisms: Absorption interference and CYP induction. Every call is cited to either a clinical reference (PMID) or the British National Formulary. Anything not on this list is either still to be assessed or beyond our database scope. The checker beneath surfaces assessments by supplement, and the missing-item form at the bottom of the page routes any uncatalogued supplement into our next curation pass.
Documented interactions
Last reviewed 15 June 2026. Each interaction below lists the evidence its assessment drew on: some rest on studies of the exact pair, others on mechanism evidence, where a citation may support one part of the reasoning rather than the exact combination. The evidence line on each entry says which.
Absorption interference
Amber Does Calcium interact with ?
Calcium carbonate, the most common supplement form, needs stomach acid to dissolve, so omeprazole can reduce how much calcium you absorb from it. Calcium citrate does not depend on stomach acid and is the better choice on a long-term PPI. If you stay on carbonate, taking it with food rather than on an empty stomach also helps.
Evidence: Supported by human study data.
Amber Does Iron interact with ?
Non-haem iron from supplements absorbs less well in a low-acid stomach, so chronic omeprazole use reduces iron uptake from a standard ferrous sulphate or ferrous fumarate tablet. Iron bisglycinate is less pH-dependent and a better choice on a long-term PPI. Always confirm ferritin is in the deficient range before supplementing iron.
Evidence: Supported by human study data.
Amber Does Magnesium interact with ?
Long-term omeprazole use is associated with low blood magnesium in about 1 in 5 chronic users. Supplementing magnesium is generally helpful, but if you have heart, kidney, or muscle symptoms on long-term omeprazole, ask your GP for a magnesium blood test.
Evidence: Supported by human study data.
Amber Does Magnesium Glycinate interact with ?
Long-term omeprazole use is associated with low blood magnesium in about 1 in 5 chronic users. Supplementing magnesium is generally helpful, but if you have heart, kidney, or muscle symptoms on long-term omeprazole, ask your GP for a magnesium blood test.
Evidence: Supported by human study data.
Amber Does Magnesium L-Threonate interact with ?
Long-term omeprazole use is associated with low blood magnesium in about 1 in 5 chronic users. Magnesium L-threonate is still elemental magnesium, so supplementing is generally helpful, but if you have heart, kidney, or muscle symptoms on long-term omeprazole, ask your GP for a magnesium blood test.
Evidence: Supported by human study data.
Amber Does Vitamin B Complex interact with ?
A B complex contains vitamin B12, and long-term omeprazole reduces stomach acid and slows how well your body absorbs B12 from food. After about two years of daily use, B12 deficiency becomes notably more likely, and a standard B complex dose may not fully offset it. If you take omeprazole long term, ask your GP about an annual B12 blood test.
Evidence: Supported by human study data.
Amber Does Vitamin B12 interact with ?
Long-term omeprazole use reduces stomach acid and slows how well your body absorbs vitamin B12 from food. After about two years of daily use, B12 deficiency becomes notably more likely. If you take omeprazole long term, ask your GP about an annual B12 blood test.
Evidence: Supported by human study data.
Green Does Vitamin C interact with ?
Vitamin C and omeprazole are worth knowing about rather than a problem. Vitamin C is less stable when the stomach is less acidic, and acid-lowering medicines like omeprazole modestly reduce the amount of vitamin C in your blood. The drop is small, it is the medicine affecting the vitamin rather than the other way round, and it does not stop you taking a vitamin C supplement. If anything, people on long-term acid-lowering treatment are the ones who may benefit most from keeping a good vitamin C intake.
Evidence: Supported by human study data.
CYP induction
Amber Does Ginkgo Biloba interact with ?
Ginkgo can speed up how the body clears omeprazole, which may make the omeprazole work less well. This tends to matter at higher ginkgo doses rather than the standard 120 to 240mg a day. If your reflux or ulcer symptoms are not well controlled while taking both, mention the ginkgo to your GP or pharmacist.
Evidence: Supported by human study data.
What this list does not say. Pairs not flagged here are not implicitly safe. They are either not yet in our database, or fall outside our inclusion scope (food-supplement interactions only; for drug-drug interactions, the BNF is authoritative). Use the checker below to surface any supplement, and submit a missing item if you take something we have not catalogued.
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How we grade severity, choose what's in scope, and what we exclude.
Every call on this page is reasoned. We publish the full rubric for severity tiers, the medication inclusion logic, the evidence grades we accept, and what we deliberately leave out. About three thousand words. Worth reading once if you use this tool more than occasionally.
Read the full methodologyA full supplement review, built around you, not a generic stack.
The free checker answers one interaction question at a time. A Distil report reviews the bigger picture: your goals, diet, medications, current supplements and any blood results you provide, then shows what appears worth keeping, changing, adding or leaving out.
- what your diet already covers, so you are not adding a capsule for something food is already handling
- which evidence-graded compounds are worth considering for your goals, and which were considered but left out
- what to keep, change or stop from what you already take, plus the order to introduce anything new
- how your medications and complete supplement stack fit together, with daily timing and a clear point for reassessment
The interaction check is one section of the full report. You also get the reasoning behind each recommendation and the evidence references used.
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