Vitamin C and medications.
Vitamin C is in the Distil supplement database, evidence Grade A. The page below lists every medication we have explicitly assessed it against.
Vitamin C is a cofactor for collagen synthesis and an antioxidant, and it has one particularly useful interaction: it markedly improves the absorption of non-haem iron from plant foods, which helps vegetarians and vegans. On colds, the Cochrane review of the trials found that taking it regularly did not reduce how often people catch one, though it did tend to make colds modestly shorter and less severe. The everyday dose is 500 to 1,000mg, and splitting it across the day absorbs better than one large hit. Smokers need a little extra because smoking depletes it. If collagen is the point, take it alongside collagen peptides, since the body cannot build collagen without it. That is a pairing instruction rather than a reason to take vitamin C for your skin on its own: no trial in our database measures a skin, hair or nail outcome for it. It also works in an antioxidant network with quercetin. The limits are about dose and kidneys. Above 2g a day it can raise kidney stone risk in predisposed people, and in established kidney disease high doses are best avoided, with intake capped around 500mg. Some prescription interactions are worth knowing. Large daily doses may make warfarin or acenocoumarol work less well, so if you take either your INR is worth watching rather than changing your vitamin C intake quietly; and vitamin C taken together with vitamin E has been reported to lower ciclosporin levels, which matters after a transplant. The main side effect is loose stools above a gram or so. For most people, a modest split dose with food covers the benefit comfortably.
Below are the 8 documented pairs we have explicitly assessed for Vitamin C: 3 amber and 5 green. The pairs cluster around 4 mechanisms: Reduced anticoagulant effect, Reduced immunosuppressant level, Absorption interference, and Beneficial combination. Every call is cited to either a clinical reference (PMID) or the British National Formulary. Anything not listed here is either still to be assessed or beyond our database scope. The checker beneath surfaces assessments by medication, and the missing-item form at the bottom of the page routes any uncatalogued medication into our next curation pass.
Documented interactions
Last reviewed 14 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.
Reduced anticoagulant effect
Amber Does Vitamin C interact with Acenocoumarol?
Vitamin C supplements have been linked in rare reports to a reduced effect of warfarin-type blood thinners like acenocoumarol, which could lower your INR. Neither report states the dose the person was taking, so we cannot point to a level below which it stops applying. Vitamin C from food is not the concern. If you take acenocoumarol and use a vitamin C supplement, keep the dose steady and mention it to your anticoagulant clinic.
Evidence: No direct study of this exact combination yet; the caution rests on a plausible mechanism or on reports involving a related medicine.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Amber Does Vitamin C interact with Warfarin sodium?
There are rare reports of vitamin C supplements making warfarin work less well, so your INR (the blood test that shows how thinned your blood is) drops below the level you need. In both published reports the INR came back up once the vitamin C was stopped. Neither report says how much vitamin C the person was taking, so we cannot point to a dose below which this stops applying. Vitamin C from food is not the concern. If you take a vitamin C supplement alongside warfarin, tell whoever manages your warfarin so your INR can be watched, keep the dose steady, and let them know before you start or stop it.
Evidence: Supported by human study data.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Reduced immunosuppressant level
Amber Does Vitamin C interact with Ciclosporin?
There is a report that vitamin C, taken together with vitamin E, lowered ciclosporin blood levels in heart transplant patients by around a third. Ciclosporin has to stay within a tight range to stop the body rejecting a transplant, so a drop like that matters. If you have a transplant or take ciclosporin for another reason, do not start a vitamin C supplement without talking to your transplant team, who can check your ciclosporin level if anything changes. The same report found no effect on tacrolimus.
Evidence: Limited human data, from small studies or case reports.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Absorption interference
Green Does Vitamin C interact with Esomeprazole?
Vitamin C and esomeprazole are worth knowing about rather than a problem. Vitamin C is less stable when the stomach is less acidic, and acid-lowering medicines like esomeprazole 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.
Green Does Vitamin C interact with Lansoprazole?
Vitamin C and lansoprazole are worth knowing about rather than a problem. Vitamin C is less stable when the stomach is less acidic, and acid-lowering medicines like lansoprazole 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.
Green Does Vitamin C interact with Omeprazole?
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.
Green Does Vitamin C interact with Pantoprazole?
Vitamin C and pantoprazole are worth knowing about rather than a problem. Vitamin C is less stable when the stomach is less acidic, and acid-lowering medicines like pantoprazole 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.
Beneficial combination
Green Does Vitamin C interact with Levothyroxine?
Vitamin C and levothyroxine can be a helpful pairing rather than a problem, especially if you have a stomach condition that lowers your stomach acid. Levothyroxine is absorbed better when the stomach is acidic, and taking it with vitamin C improved thyroid blood results in people whose levels had been hard to control. For most people with a normal stomach this makes little difference, and levothyroxine is still best taken on an empty stomach. If your thyroid levels have been difficult to settle, it is worth raising vitamin C with your prescriber rather than changing anything on your own.
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. Use the checker below to surface any medication, 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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