Verified Supplement Data

Third-Party Tested Vitamin C Supplements

Buy Nature Made Vitamin C 500 mg: it is on USP’s Verified list (500 mg tablet, listed by name) and costs $0.08 a day. Only 3 of the 14 vitamin C products we checked are on a testing list.

By Erin Rose Updated November 3, 2026 How we score

Our recommendation

Buy Nature Made Vitamin C 500 mg

USP lists this exact tablet. One tablet gives 500 mg and costs $0.08 a day, less than the other two products on a list.

Buy on Amazon · $7.49

Which vitamin C supplements are third-party tested? (3)

An outside program checked each of these and lists it by name. Tap a badge to see the program.

  1. Our pick

    Nature Made Vitamin C 500 mg

    USP Verified

    500 mg of vitamin C in 1 tablet. USP lists the 500 mg tablet by name.

    $0.08
    list price a day

    Buy on Amazon · $7.49

  2. Nature Made Vitamin C 1000 mg

    USP Verified

    1,000 mg of vitamin C in 1 tablet. USP lists the 1,000 mg tablet by name.

    $0.16
    list price a day

    Buy on Amazon · $8.53

  3. Liposomal form

    Codeage Liposomal Vitamin C+

    NSF/ANSI 173

    1,500 mg of vitamin C in 3 capsules. Comes with elderberry and quercetin. NSF lists Liposomal Vitamin C+. A 2-pack of 180-capsule bottles.

    $0.67
    list price a day

    Buy on Amazon · $63.99

Cost a day = each brand’s list price divided by the servings in the pack, one serving a day, checked October 19, 2026. The Amazon price on the button can differ. We count a listing only when it names the same product.

Also on a testing list

These vitamin C products are on a list too. USP read from its September 22, 2026 snapshot; NSF/ANSI 173 from its August 25, 2026 snapshot.

Cost a day of tested vitamin C

Nature Made Vitamin C 500 mg costs $0.08 a day. That is the lowest cost a day of the 14 products we compared.

If you want 1,000 mg at once, Nature Made Vitamin C 1000 mg costs $0.16 a day, the same per 1,000 mg as two 500 mg tablets ($0.16). The body absorbs less as the dose goes up. A 200 mg dose was fully absorbed in an NIH study of 7 healthy men, and less of 500 mg and above (Levine 1996), so a smaller tablet is enough for most adults.

Not on a testing list (11)

We also checked these 11. We did not find them on a USP or NSF list.

  1. Nature’s Bounty Vitamin C 1000 mg

    Not on a testing list

    1,000 mg of vitamin C in 1 caplet.

    $0.12
    list price a day

    Buy on Amazon · $6.97

  2. NOW C-1000 with Bioflavonoids

    Not on a testing list

    1,000 mg of vitamin C in 1 capsule. Comes with citrus bioflavonoids.

    $0.13
    list price a day

    Buy on Amazon · $18.50

  3. NOW C-1000 Buffered

    Not on a testing list

    1,000 mg of vitamin C in 1 tablet. Buffered tablet.

    $0.20
    list price a day

    Buy on Amazon · $19.84

  4. Solgar Vitamin C 1000 mg

    Not on a testing list

    1,000 mg of vitamin C in 1 tablet.

    $0.12
    list price a day

    Buy on Amazon · $10.42

  5. Thorne Vitamin C with Flavonoids

    Not on a testing list

    500 mg of vitamin C in 1 capsule. NSF lists other Thorne vitamin C products, not this one.

    $0.26
    list price a day

    Buy on Amazon · $23.00

  6. Doctor’s Best Vitamin C 1000 mg

    Not on a testing list

    1,000 mg of vitamin C in 1 veggie capsule. Q-C form.

    $0.17
    list price a day

    Buy on Amazon · $18.99

  7. Bluebonnet Vitamin C 1000 mg

    Not on a testing list

    1,000 mg of vitamin C in 1 vegetable capsule.

    $0.22
    list price a day

    Buy on Amazon · $29.56

  8. Pure Encapsulations Ascorbic Acid

    Not on a testing list

    1,000 mg of vitamin C in 1 capsule. Hypoallergenic capsule.

    $0.25
    list price a day

    Buy on Amazon · $22.50

  9. American Health Ester-C 1000 mg

    Not on a testing list

    1,000 mg of vitamin C in 1 capsule. Ester-C form, with citrus bioflavonoids.

    $0.23
    list price a day

    Buy on Amazon · $17.00

  10. Core Med Science Liposomal Vitamin C

    Not on a testing list

    1,000 mg of vitamin C in 3 softgels. NSF lists Core Med’s plain 500 mg capsule, not this liposomal softgel.

    $0.83
    list price a day

    Buy on Amazon · $24.99

  11. LivOn Lypo-Spheric Vitamin C

    Not on a testing list

    1,000 mg of vitamin C in 1 packet. Liposomal packet.

    $1.43
    list price a day

    Buy on Amazon · $43.95

What does each program check?

ProgramWhat it tells you
NSF/ANSI 173Checks that what the label says is in the bottle, and that lead, mercury, arsenic and cadmium stay under set limits. It does not screen for banned substances.
USP VerifiedChecks that the tablet holds the vitamin C on the label in the stated amount, that it breaks down so the body can use it, and that contaminants such as lead stay under set limits.

How to check your own bottle

  1. Look for the USP Verified mark or the NSF mark on the bottle.
  2. Search USP’s list or NSF’s list for the exact product name and strength. A brand’s 500 mg tablet can be listed while its 1,000 mg gummy is not.
  3. Read the Supplement Facts for vitamin C in mg per serving. For liposomal products, check how many capsules make a serving.
  4. Pick a dose that fits what you need, and stay under the 2,000 mg upper limit. See the dosage guide.

Comparing on more than testing? See the best vitamin C supplement, or how the forms compare.

Questions

Which vitamin C supplements are third-party tested?

Nature Made Vitamin C 500 mg and Nature Made Vitamin C 1000 mg are on USP’s Verified list. Codeage Liposomal Vitamin C+ is on NSF/ANSI 173. The other 11 we checked are on no public list. Other products are also listed, such as Thorne Vitamin C 1,000 mg capsules (NSF/ANSI 173) and Kirkland Signature Vitamin C 1000 mg tablets (USP).

Is Nature Made vitamin C USP Verified?

Several Nature Made vitamin C products are, and USP lists each by name: the 500 mg and 1000 mg tablets, a 500 mg with rose hips caplet, 500 mg softgels, chewables and gummies. Check that your bottle is one of those, since a brand can have products that are not listed.

Is Thorne vitamin C third-party tested?

Some of it is. NSF/ANSI 173 lists Thorne Vitamin C 1,000 mg and 500 mg capsules and Thorne High Potency Vitamin C powder. The Thorne product we compare, Vitamin C with Flavonoids, is not on that list, so we count it as not listed.

What is the difference between third-party tested and certified?

A brand can pay a lab to test its own batches and then say “third-party tested.” A program such as USP or NSF lists the exact product after its own review and audits. Search the program’s list for the product name; that is the check that counts.

Is Codeage Liposomal Vitamin C+ worth the price?

Only if you want a liposomal capsule. It costs $0.67 a day for 1,500 mg, about 8 times a Nature Made Vitamin C 500 mg tablet, and NSF lists it by name. Plain ascorbic acid in a tablet is fully absorbed at 200 mg (Levine 1996, 7 men); see the forms compared.

How much vitamin C do I need?

Adults need 75 mg (women) to 90 mg (men) a day, and the adult upper limit is 2,000 mg (NIH). A 500 mg tablet already covers that. If you have had kidney stones, ask your doctor before taking large doses. See the dosage guide.

Sources

  1. USP Verified Dietary Supplements and NSF/ANSI 173: each program’s own list, searched by product name. USP as of its September 22, 2026 snapshot, NSF/ANSI 173 as of its August 25, 2026 snapshot.
  2. NIH Office of Dietary Supplements. Vitamin C fact sheet for health professionals (updated July 31, 2025).
  3. Levine M, et al. “Vitamin C pharmacokinetics in healthy volunteers: evidence for a recommended dietary allowance.” Proc Natl Acad Sci USA. 1996. PubMed 8623000