Home Ingredients Cupric Oxide
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Cupric Oxide

Evidence Level
Limited
2 Clinical Trials
4 Documented Benefits
2/5 Evidence Score

Cupric oxide (copper(II) oxide, CuO) is a cheap, high-elemental copper compound containing roughly 80% copper by weight, which makes it look impressive on a Supplement Facts label. It is widely used as a low-cost copper source in mass-market multivitamins. Critical honest framing: despite its high copper percentage, cupric oxide is poorly soluble and poorly bioavailable. Animal feeding studies show its copper is essentially unavailable for absorption, and a Journal of Nutrition editorial concluded it should not be used as a copper supplement for animals or humans. It is the cautionary 'looks good on the label, barely absorbed' form.

Studied Dose RDA 0.9 mg/day elemental copper; UL 10 mg/day. Mass-market multivitamins often list 0.5–2 mg copper as cupric oxide, but absorbed copper is far lower.
Active Compound Copper(II) oxide, CuO — poorly soluble inorganic compound; high elemental copper (~80%) but very low bioavailability

Benefits

High elemental copper on the label

Cupric oxide contains roughly 80% copper by weight, more than any common nutritional form, so a tiny amount satisfies a large label claim at low cost. This is the main reason manufacturers choose it, though the label number does not reflect absorbed copper.

Supported by Trial 1, Trial 2

Inexpensive copper for fortification

As a cheap, stable, odorless powder, cupric oxide is convenient to blend into mass-market multivitamins. It can contribute to a product's stated copper content, but better-absorbed forms are preferable when the goal is actually raising copper status.

Supported by Trial 2, Trial 1

Provides copper only if it dissolves

Copper is essential for antioxidant, iron-handling, and connective-tissue enzymes. Cupric oxide can in principle supply that copper, but only the small fraction that dissolves and is absorbed contributes, which is why more soluble forms are generally recommended.

Supported by Trial 1, Trial 2

Stable, shelf-friendly ingredient

Cupric oxide is chemically stable and does not readily oxidize other nutrients in a blend, which helps formulation shelf life. Its drawback is the same property that makes it stable also makes it poorly soluble and poorly absorbed in the gut.

Supported by Trial 1, Trial 2

Mechanism of action

1

Poor solubility limits absorption

Cupric oxide is largely insoluble in water and only sparingly soluble in stomach acid, so little ionic copper is released for uptake by the intestinal CTR1 transporter. Bioavailability depends on dissolution, and CuO dissolves too poorly to deliver much copper.

2

Near-zero measured bioavailability

In controlled chick feeding studies measuring liver copper accumulation, cupric oxide provided essentially no bioavailable copper compared with copper sulfate, while cuprous oxide and copper-lysine matched sulfate. The defect is specific to cupric oxide.

3

Copper enzyme roles when absorbed

Any copper that is absorbed supports ceruloplasmin, copper-zinc superoxide dismutase, lysyl oxidase, and cytochrome c oxidase. The limitation with cupric oxide is delivery, not the downstream biochemistry of copper itself.

Clinical trials

1
Cupric oxide bioavailability essentially zero — feeding study
PubMed

Two-week chick feeding trial comparing copper bioavailability of cupric oxide, cuprous oxide, and a copper-lysine complex against copper sulfate, using liver copper accumulation as the endpoint.

Young chicks (controlled feeding).

Cuprous oxide and copper-lysine furnished copper as efficiently as copper sulfate, but cupric oxide provided no bioavailable copper to the chicks. This directly demonstrates that the high elemental percentage of cupric oxide does not translate into absorbable copper.

2
Authoritative position: do not use cupric oxide
PubMed

Journal of Nutrition editorial reviewing the accumulated evidence on cupric oxide copper bioavailability in animals and humans.

Evidence review/editorial.

The editorial concluded that the copper in analytical-grade cupric oxide is unavailable for absorption, with bioavailability relative to copper sulfate not significantly different from zero, and stated plainly that cupric oxide should not be used as a copper supplement for either animals or humans.

Side effects and drug interactions

Common Potential side effects

Poorly absorbed, so it may fail to correct or maintain copper status despite a high label dose.
Relying on cupric oxide for copper while taking zinc raises the risk of copper deficiency.
Copper deficiency can cause anemia, low white blood cells, and nerve problems over time.
People with Wilson's disease must still avoid all supplemental copper, including cupric oxide.
Any absorbed excess copper above the 10 mg/day upper limit can stress the liver.

Important Drug interactions

High-dose zinc further reduces the already-low copper uptake from cupric oxide.
Antacids and acid-suppressing drugs lower stomach acid, worsening cupric oxide dissolution.
Copper chelators (penicillamine, trientine) for Wilson's disease are opposed by any copper source.
Because absorption is poor, cupric oxide is a weak choice for correcting drug-induced copper loss.

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Frequently asked questions about Cupric Oxide

What is cupric oxide (copper oxide)?

Cupric oxide is an inexpensive inorganic copper form often found in multivitamins. However, it is poorly absorbed, so despite its high copper content on paper, little is actually taken up by the body.

Is copper oxide a good supplement form?

Not really. Cupric oxide is one of the least bioavailable copper forms, which is why it is sometimes described as a filler in cheap multivitamins. Chelated forms like copper bisglycinate or copper gluconate are better absorbed.

How much cupric oxide should I take?

Copper needs are small (about 900 mcg per day RDA). Because cupric oxide is poorly absorbed, the listed amount overstates what you actually get. If copper supplementation matters to you, choose a more absorbable form.

Is cupric oxide safe?

It is considered safe at the small amounts in supplements, mainly because so little is absorbed. The bigger issue is effectiveness rather than safety; for meaningful copper intake, a better-absorbed form is preferable.

What is Cupric Oxide?

Cupric oxide (copper(II) oxide, CuO) is a cheap, high-elemental copper compound containing roughly 80% copper by weight, which makes it look impressive on a Supplement Facts label. It is widely used as a low-cost copper source in mass-market multivitamins.

What is Cupric Oxide used for?

Cupric Oxide is researched primarily for Immune Support, Antioxidant, and Cardiovascular. Cupric oxide contains roughly 80% copper by weight, more than any common nutritional form, so a tiny amount satisfies a large label claim at low cost.

What is the recommended dosage of Cupric Oxide?

The clinically studied dose is RDA 0.9 mg/day elemental copper; UL 10 mg/day. Mass-market multivitamins often list 0.5–2 mg copper as cupric oxide, but absorbed copper is far lower. Always follow the product label and check with a healthcare provider for personal advice.

Is Cupric Oxide safe, and does it have side effects?

For most healthy adults, Cupric Oxide is well tolerated at studied doses. Reported effects can include: Poorly absorbed, so it may fail to correct or maintain copper status despite a high label dose. Relying on cupric oxide for copper while taking zinc raises the risk of copper deficiency. It may also interact with some medications. Cupric Oxide is not right for everyone, so check with a healthcare provider first if you are pregnant or breastfeeding, have a medical condition, or take prescription medication.

Does Cupric Oxide interact with any medications?

Possible interactions include: High-dose zinc further reduces the already-low copper uptake from cupric oxide. Antacids and acid-suppressing drugs lower stomach acid, worsening cupric oxide dissolution. If you take prescription medication, check with a pharmacist or doctor before using it.

How strong is the scientific evidence for Cupric Oxide?

NutraSmarts rates the evidence for Cupric Oxide as Limited (2 out of 5). It is backed by 2 clinical trials and 3 cited references summarized on this page. A higher rating reflects more, larger, and better-designed human studies.

References(3 citations)

Evidence ratings on NutraSmarts are based on the totality of human clinical research, with emphasis on randomized controlled trials, meta-analyses, and systematic reviews. The references below directly support claims made throughout this page.

  1. Baker DH. Cupric oxide should not be used as a copper supplement for either animals or humans. J Nutr. 1999;129(12):2278-9. doi: 10.1093/jn/129.12.2278.PubMedUsed to support: Editorial concluding cupric oxide copper is essentially unavailable for absorption (relative bioavailability near zero) and should not be used as a copper supplement — the core honest-framing source.
  2. Baker DH, Odle J, Funk MA, Wieland TM. Research note: bioavailability of copper in cupric oxide, cuprous oxide, and in a copper-lysine complex. Poult Sci. 1991;70(1):177-9. doi: 10.3382/ps.0700177.PubMedUsed to support: Feeding study showing cupric oxide provided no bioavailable copper to chicks while cuprous oxide and copper-lysine matched copper sulfate — direct evidence of poor cupric oxide absorption.
  3. Turnlund JR, Keyes WR, Anderson HL, Acord LL. Copper absorption and retention in young men at three levels of dietary copper by use of the stable isotope 65Cu. Am J Clin Nutr. 1989;49(5):870-8. doi: 10.1093/ajcn/49.5.870.PubMedUsed to support: Provides the human copper-absorption baseline for well-absorbed dietary copper, against which cupric oxide's near-zero bioavailability is the cautionary contrast.