Orotic Acid

What is Orotic Acid?

Orotic acid is a pyrimidine carboxylic acid, formula C5H4N2O4, molecular weight 156.1, that your liver and every dividing cell makes on demand while building the pyrimidine bases of DNA and RNA. It was first isolated from cow milk whey, hence the name. Average cow milk runs about 0.62 mmol per liter, roughly 96 mg, so a glass supplies 20 to 25 mg without anyone marketing it.

For part of the mid twentieth century it was labeled vitamin B13, on the strength of animal growth-factor work that was measuring something the animals already made themselves. The designation was dropped. Labels still print it.

Almost nobody buys it alone. It is sold as the anion half of a mineral salt, and the case for those products rests entirely on what the orotate is said to do for the mineral attached to it.

Common Names

• Orotic acid, orotate

• Vitamin B13 (obsolete designation)

• 6-carboxyuracil, uracil-6-carboxylic acid

Primary Active Compounds

• Magnesium orotate dihydrate, about 6.6 percent magnesium by weight

• Lithium orotate, about 3.8 mg elemental lithium per 100 mg of salt

Key Nutritional Note

Orotic acid is not a vitamin and not essential. There is no recommended intake and no biomarker of insufficiency. There is a biomarker of excess, and hospitals use it.

Everything else here follows from that one asymmetry.

Primary Functions & Benefits

Orotic acid's real job is internal, not nutritional.

• It is the committed pyrimidine intermediate. Orotate reacts with PRPP to form OMP, decarboxylated to UMP, from which UTP, CTP, and every other pyrimidine nucleotide follows.

• In hypoxic cardiac tissue, added orotate raises nucleotide and glycogen levels in animals. That is the story behind magnesium orotate's cardiac marketing.

In the mineral salts, orotate is a poorly soluble counter-ion, so the salt dissolves slowly and plausibly causes less osmotic gut effect than fast-dissociating magnesium salts. That is a formulation property, not a transport mechanism, and marketing copy conflates the two.

Who Should Take Orotic Acid

The honest list is short, and none of it is about the orotate.

• People prescribed magnesium orotate as a magnesium source. It is a licensed medicine in parts of Europe as Magnerot.

• People with severe heart failure whose cardiologist adds magnesium, and who accept that one 79-patient trial is the entire supporting dataset.

• Nobody needs orotic acid as a nutrient. No population or condition leaves the body unable to make enough.

If you are considering an orotate because a label said it absorbs better, read section 12.

Who Should AVOID or Use Caution

Contraindications

• Anyone with a suspected urea cycle disorder, especially ornithine transcarbamylase deficiency. Supplemental orotic acid corrupts the most useful diagnostic test they have.

• People taking prescription lithium. Adding an over-the-counter lithium salt is uncontrolled dosing of a drug with a narrow therapeutic window.

• Pregnancy and breastfeeding. EFSA noted the absence of developmental toxicity data on orotic acid.

Use Caution

• Significant liver disease. Chronic gram-level orotic acid has never been studied for effects on human liver lipids.

• Reduced kidney function, if considering lithium orotate. Lithium clearance is renal, and impaired clearance is the standard route to toxicity.

• Stacking products. EFSA calculated that combining marketed orotates could push daily orotic acid intake past 11 grams.

Critical Safety Point

If you take an orotate and later present with confusion, vomiting, or hyperammonemia, say so. Elevated urinary orotic acid is how clinicians work out which enzyme failed, and your supplement makes that test uninterpretable.

Recommended Dosages

There is no established intake because there is no requirement. These are the doses used and sold.

Magnesium orotate, clinical trials

6,000 mg daily for one month, then 3,000 mg for eleven months, in the MACH heart failure trial. At 6.56 percent magnesium, 3,000 mg supplies about 197 mg of magnesium and about 2,500 mg of orotic acid.

Magnesium orotate, consumer products

Typically 500 to 1,500 mg of salt per serving, or 33 to 100 mg of magnesium. Many labels print only salt weight.

Lithium orotate, consumer products

Usually 100 to 130 mg of salt per capsule, roughly 4 to 5 mg of elemental lithium. A 900 mg dose of lithium carbonate supplies about 169 mg, so the supplement is 2 to 5 percent of a psychiatric dose.

Duration

The longest controlled human exposure on record is 12 months, in 40 patients. Multi-year gram-level intake has no safety data.

Timing & Administration

• Magnesium orotate dissolves slowly, so take it with food and split it across the day. Splitting also reduces the gut load.

• Lithium orotate is taken once daily. If you take it, take it at a fixed time, because serum lithium interpretation depends on hours since the last dose.

Benefits of Taking Orotic Acid

Graded by what human evidence supports.

• Magnesium orotate in severe congestive heart failure has one positive controlled trial. Stepura and Martynow randomized 79 NYHA class IV patients on optimal therapy, International Journal of Cardiology, 2009. One-year survival was 75.7 percent against 51.6 percent on placebo, p under 0.05.

• It was single-center and has never been replicated. It also carries a confound rarely mentioned: 197 mg of magnesium is an ordinary dose, given to a population where depletion is common. That may be a magnesium result in an orotate label.

• Exercise duration improved in a 1998 double-blind pilot of 14 coronary patients at 3 g daily. Fourteen patients is a pilot, not a finding.

• The same dose for 90 days did nothing for idiopathic male infertility in a randomized placebo-controlled study of 20 men, Magnesium Research 2003.

• Lithium orotate has no completed human efficacy trial. Zinc, calcium, and copper orotates have none either.

Potential Negatives & Side Effects

• Gastrointestinal upset and loose stools, usually from the mineral. Orotate salts tend to be gentler than magnesium oxide or citrate.

• Label opacity. A bottle listing "magnesium orotate 500 mg" is stating salt weight, not the 33 mg of magnesium you get. That is the most common practical harm here, people believing they are magnesium-replete on a token dose.

• For lithium orotate, the absence of the monitoring that accompanies the prescription drug. Prescribed lithium comes with serum levels, thyroid panels, and renal checks. The supplement comes with none, and users often do not know their product contains a drug.

Deficiency Symptoms

Orotic acid is not an essential nutrient, so there is no deficiency state to describe. Humans synthesize it continuously as a normal intermediate in de novo pyrimidine biosynthesis, and no diet, illness, or life stage creates a shortfall. Elevated levels signal disease rather than sufficiency, reversing the usual logic of these articles.

What orotic acid addresses

• Nothing, as a nutrient. No clinical picture follows from low intake, because intake is irrelevant to supply.

• The only orotic acid disorder is the inability to use it. Hereditary orotic aciduria, reported in roughly 20 people worldwide, is a UMP synthase defect in which orotic acid piles up because the next enzyme is missing. The treatment, approved in 2015, is uridine triacetate, given downstream of the block. More orotic acid would be backwards.

Bottom line

If a label implies you might be low in vitamin B13, it is describing a condition that does not exist in human medicine.

Toxicity Symptoms

At high intake

• The dominant preclinical signal is hepatic steatosis. Rats fed 1 percent orotic acid develop fatty liver reliably, first reported by Standerfer and Handler in 1955 and used ever since as a standard steatosis model.

• That model is species-dependent, and the qualification matters. Korycka-Dahl and colleagues fed rhesus monkeys the same 1 percent diet for 10 weeks and found normal liver lipids and normal hepatic morphology, Journal of Dairy Science, 1979. Rats are unusually sensitive because orotic acid blocks their hepatic VLDL secretion.

• Human data at supplemental doses are absent. Nobody has fed gram-level orotic acid to people and imaged their livers. The rodent finding neither establishes human risk nor rules it out.

• Animal studies also show tumour promotion at 0.5 to 2 percent of the diet. That is promotion in already-initiated tissue, not initiation.

• Acute lithium toxicity is documented. Pauzé and Brooks reported an 18-year-old who took 2.16 g of lithium orotate, Journal of Medical Toxicology, 2007, with nausea, vomiting, and tremor at a serum lithium of 0.40 mEq per liter, well under the usual 1.5 mEq per liter threshold.

Signs to reduce or stop

• Nausea, tremor, unsteady gait, slurred speech, or excessive thirst and urination on any lithium product. Stop and get a serum lithium level.

• Unexplained ALT or AST rises on chronic gram-level use.

General note

The realistic hazard is not one large dose. It is chronic gram-level intake of a compound with a 50 mg per kg per day no-effect level, bought by people who think it is a vitamin, from a shelf that also sells an unmonitored psychiatric drug.

How Orotic Acid Works

Pyrimidines are the C, T, and U letters of the genetic alphabet, and cells build them backwards from purines. A purine base is assembled directly on its ribose sugar. A pyrimidine ring is built whole first, then handed a sugar. Orotic acid is that finished ring.

Carbamoyl phosphate and aspartate condense in the cytoplasm and cyclize to dihydroorotate. That crosses to the inner mitochondrial membrane, where dihydroorotate dehydrogenase oxidizes it to orotate. Orotate returns to the cytoplasm and meets PRPP, an activated ribose phosphate. UMP synthase then does the last two steps in one enzyme: it attaches the sugar to make orotidine monophosphate, then decarboxylates that to UMP, from which every downstream pyrimidine comes. One consequence matters clinically. When the urea cycle backs up, carbamoyl phosphate escapes into this pathway and orotic acid pours into urine. Hence the test.

Now the part that undercuts the delivery premise. An orotate mineral salt is an ionic pair, and orotic acid's carboxyl group has a pKa near 2. Stomach acid sits at pH 1.5 to 3. There the orotate anion picks up a proton, the salt comes apart, and the mineral is released as a free hydrated cation into the same pool it would enter from any other salt. Hajek, Munthe and Licht laid this out for lithium orotate in the British Journal of Psychiatry in 2026, noting that no study has shown a stable lithium orotate complex in physiological fluids and that the orotate and the carbonate have comparable pharmacokinetics after oral dosing. Nieper's carrier has to survive the stomach to do its job. The chemistry says it does not.

Synergistic Supplements

• Vitamin B6 with magnesium is a genuine pairing, and applies to magnesium orotate as to any magnesium salt.

• Uridine, not orotic acid, is the useful pyrimidine precursor in humans. It enters salvage downstream of the enzyme that fails in hereditary orotic aciduria, which is why it is the approved drug and orotic acid is not.

Stacking multiple orotate salts produces no additive benefit. It does produce additive orotic acid.

Interactions & What NOT to Take

• NSAIDs, ACE inhibitors, ARBs, and thiazide diuretics all reduce lithium clearance. A Dutch case in Tijdschrift voor Psychiatrie in 2017 describes a 38-year-old woman whose team withheld metronidazole and naproxen because she reported taking lithium, before finding it was an internet lithium orotate supplement and her serum level was under 0.05 mmol per liter.

• Teriflunomide and leflunomide inhibit dihydroorotate dehydrogenase, the enzyme immediately upstream of orotate.

• Tetracyclines, fluoroquinolones, bisphosphonates, and levothyroxine bind divalent minerals. Separate by two hours.

• Before any urine organic acid panel or ammonia workup, stop the product and tell the clinician.

Special Considerations

Hans Nieper died in 1998. His program, which paired orotates with laetrile, calcium EAP, and a theory that geopathic earth radiation caused cancer, drew an FDA import alert in August 1986, and in 1993 the FDA seized and destroyed illegally manufactured Nieper orotate products. That does not make orotate chemistry wrong. It explains why the transport claim was never put through the trials that would have settled it.

Lithium orotate deserves separate handling because the stakes differ. Interest surged after Aron and colleagues published in Nature in August 2025, showing lithium is depleted in the brains of people with mild cognitive impairment and that lithium orotate, chosen because it binds amyloid less than other salts, prevented pathology in mice. A 2023 study found it blocked amphetamine-induced hyperlocomotion in mice at a tenth the dose of lithium carbonate. Both are mice. The human data amount to a nine-participant imaging study at 5 mg daily that measured brain lithium but no clinical outcome, and a 211-person survey where side effects and withdrawal were commoner than expected.

Research Status & Evidence Quality

Strong Evidence For

• Urinary orotic acid as a discriminator in urea cycle disorders. Elevated in ornithine transcarbamylase deficiency, citrullinemia, and argininemia, normal in carbamoyl phosphate synthetase deficiency, which makes it diagnostic rather than merely abnormal.

• Orotic acid as an inducer of hepatic steatosis in rats at 1 percent of the diet.

Moderate Evidence For

• Magnesium orotate as a usable, well-tolerated magnesium source with less osmotic gut effect than soluble salts.

Emerging / Preliminary Evidence For

• Magnesium orotate in severe heart failure. One trial, 79 patients, unreplicated for over fifteen years.

• Low-dose lithium for cognitive protection. Mouse data plus epidemiology, no completed human trial of the orotate salt.

Research Limitations

• No controlled human absorption study compares any orotate salt against another salt of the same mineral. The founding claim of the category is untested after fifty years.

• Where orotate salts have been compared in animals, the result went the wrong way. Zinc orotate was absorbed more slowly than zinc sulfate in rabbits in 1982, being the least soluble salt tested.

• EFSA has twice found that safety at proposed use levels cannot be established, in 2009 across ten mineral orotates and again in July 2025 for magnesium orotate dihydrate.

Summary & Key Takeaways

Orotic acid is a real molecule doing real work, and none of that work depends on you eating any. Your cells make it, use it within seconds, and normally never let it accumulate. When it does accumulate and spills into urine, something upstream has broken. Selling it as a nutrient inverts that meaning. Selling it as a delivery vehicle asks you to accept a mechanism never shown in a human and argued against by basic chemistry.

Bottom Line

Magnesium orotate is a reasonable magnesium salt with one unreplicated heart failure trial and a lot of carrier weight. Every other orotate is a normal mineral dose sold at a premium for a transport claim from 1970s Hannover. Read the label for elemental content, not salt weight, and judge the product on its mineral.

Key Safety Points

• Lithium orotate is a drug sold as a supplement, with no serum levels, thyroid checks, or renal monitoring. Do not combine it with prescription lithium.

• Disclose orotate use before any metabolic or hyperammonemia workup, or you invalidate the test.

• Rats fed 1 percent orotic acid get fatty liver. Rhesus monkeys on the same diet did not. Humans have not been studied at these doses, and anyone calling it proven safe or proven harmful is past the evidence.

Special Note

There is a tell worth carrying to other shelves. When a supplement's selling point is the carrier rather than the active ingredient, ask what happens to that carrier in stomach acid. If the pair comes apart at pH 2, you did not buy a delivery system. You bought the mineral, plus several hundred milligrams of something nobody had a reason to make you swallow.