DOSEGUY

Vitamin C

most data

Also seen as: Injectable, Ascorbic Acid

The Dose Guy’s verdict
Sep 1, 2026
5 sources

Everyone has an opinion on vitamin C, and most of them are too generous. At normal oral doses it does real, small things: shortens colds modestly, supports iron uptake, nudges blood pressure down. Fine. The problem is the megadose and IV claims. Three trials of intravenous vitamin C in critical illness have now landed, and all three showed harm, not benefit. The ceiling for this compound is a lot lower than the marketing suggests.

Would I take it?Oral is fine. IV is hype.

What it is

Vitamin C is the water-soluble ascorbate your body cannot make and must get from food or supplementation. It works as an antioxidant, supports collagen synthesis, and aids iron uptake from plant foods. The biology is real and well mapped.

The reason the dose conversation matters more here than with most vitamins is pharmacokinetics. Oral absorption saturates: bioavailability is complete at a 200 mg dose but drops at 500 mg and above, and plasma concentration plateaus around 1000 mg daily no matter how much you swallow. Intravenous vitamin C bypasses that plateau entirely, reaching plasma concentrations far higher than any oral regimen can produce. That gap is why IV clinics sell it as a different drug, and why the IV trials matter so much. Higher is not always better.

What the research shows

The oral data is solid and modest. The IV data is now in, and it is bad:

Regular vitamin C supplementation shortened common-cold duration by 8% in adults and 14% in children, but did not reduce cold incidence in the general population.Cochrane 2013 · meta-analysis · common-cold trials
In marathon runners, skiers, and soldiers in subarctic conditions, regular vitamin C supplementation halved common-cold incidence, pooled RR 0.48.Cochrane 2013 · 5 exertion trials · n=598
In ICU patients with sepsis, intravenous vitamin C at 50 mg/kg every 6 hours produced worse outcomes: death or persistent organ dysfunction at day 28 occurred in 44.5% of the vitamin C group versus 38.5% on placebo.NEJM 2022 · LOVIT RCT · n=872
In severe burn injury, 28-day mortality was 15.0% with intravenous vitamin C and 7.6% with placebo. The trial stopped early at the first interim analysis.VICTORY 2026 · phase 3 RCT · n=238
After cardiac arrest, intravenous vitamin C at 10 g daily produced less improvement in organ-function scores than placebo, with worse renal function and neurological outcomes.VITaCCA 2026 · phase 2 RCT · n=273
Total vitamin C intake of at least 1000 mg daily was associated with incident kidney stones in men, HR 1.43. The association was not found in women or from dietary sources alone.Am J Kidney Dis 2016 · prospective cohorts · n=197,271

Realistic protocols

For the oral floor, which is what most people should care about: eat your fruit and vegetables, and if you want a supplement, 200 to 500 mg daily is the sweet spot where absorption is still efficient and you are well above deficiency without pushing into kidney-stone territory. Going past 1000 mg daily adds nothing to plasma levels and starts adding urinary oxalate, which is the stone risk.

If you train hard or live under physical stress, the cold-incidence data gets more interesting. Marathon runners, skiers, and soldiers in subarctic conditions saw their cold risk cut roughly in half with regular supplementation. For everyone else, it shortens the cold you catch by less than a day and does not prevent it.

Skip the IV drip. Three trials in critical illness, LOVIT in sepsis, VITaCCA after cardiac arrest, VICTORY in severe burns, all showed harm signals. The evidence does not support routine intravenous vitamin C in sepsis, alone or combined with hydrocortisone and thiamine. The pharmacologic-dose story is over.

Daily oral200–500 mgFull absorption, well above deficiency, below the stone-risk line.
Upper limit1000 mg/dayPlasma saturates here. Past this you are paying for oxalate, not benefit.
IVSkip itThree large RCTs showed harm in critical illness. The hype is over.

Side effects

Oral vitamin C at reasonable doses is very safe. The risks show up at high doses and via IV:

commonGI upset, diarrhea, and nausea at oral doses above 2000 mg. The gut is telling you to stop.
monitorKidney stones: in men, supplemental vitamin C at 1000 mg or more daily carried a 19% higher stone risk. Total intake at the same threshold carried a 43% higher risk. No association in women or from dietary sources alone.
monitorUrinary oxalate rises measurably with supplementation above 1000 mg. No effect on urinary citrate or calcium.
unknownIV vitamin C in critical illness showed harm signals across three major trials. Whether those signals extend to the elective wellness IV drip is unknown, but the direction is not encouraging.

Where to buy

PCT.zone–
$1 / 500mg vial$0.002/mg
✓ verified Sep 12
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Disguised Research–
$54.99 / unit
⚠ ⚠ Unreachable since Sep 11
✓ verified Sep 8
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