L-Ornithine

Urea cycle amino acid, adjunct for hyperammonaemia

ATC code: A16AA-L-ORNITHINE (L-Ornithine)

Brand names – supplements

NOW Foods L-Ornithine, Solgar L-Ornithine, Doctor's Best L-Ornithine

Supplements are not tested in clinical trials and are not registered as medications.

Mechanism of action

Ornithine participates in the urea cycle, the body's main pathway for ammonia disposal. Combined with aspartate it forms L-ornithine-L-aspartate (LOLA), which activates ornithine transcarbamylase and promotes ammonia conversion into urea in hepatocytes and into glutamine in perivenous hepatocytes and muscle. This mechanism underlies LOLA use in hepatic encephalopathy. Free L-ornithine as monotherapy is less studied; oral bioavailability is lower than for the aspartate combination.

Indications

Hepatic encephalopathy

Adjunct

Clinical hepatology uses not free L-ornithine but the combined drug L-ornithine-L-aspartate (LOLA). and in their joint 2014 guideline included LOLA as an adjunct option for overt hepatic encephalopathy in cirrhosis, in addition to lactulose and rifaximin. A Cochrane review in 2018 pooled 36 RCTs and found reduced mortality and improved psychometric tests with moderate certainty; the authors noted risk of bias in part of the studies. Self-administered consumer L-ornithine from iHerb does not substitute the hepatologist's prescription; the decision on LOLA is taken by the doctor after assessing the encephalopathy grade and liver function.

Sources

Cochrane: L-ornithine L-aspartate for prevention and treatment of hepatic encephalopathy in people with cirrhosis (2018)

Marketing claims without evidence base

The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.

Weight loss

Not recommended

L-ornithine is heavily marketed on iHerb and in sports shops as a fat burner and energy aid through effects on the urea cycle, creatine synthesis and growth hormone release. rejected the proposed health claims for L-ornithine in 2011 (increase in muscle mass and reduction of body fat): the submitted data did not establish a causal relationship. There are no high-quality weight loss RCTs in healthy subjects. The standard is dietary control, physical activity and, when indicated, pharmacological or bariatric care. If weight loss matters, discuss the plan with an endocrinologist or dietitian and consider a second opinion before buying L-ornithine for this purpose.

Sources

EFSA: Scientific Opinion on the substantiation of health claims related to L-ornithine and increase in muscle mass and reduction of body fat mass (2011)

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Safety

Contraindications

Hypersensitivity to ornithine
Severe renal failure (creatinine above 3 mg/dL)
Inherited urea cycle disorders

Serious adverse effects

Worsening hyperammonaemia in inherited urea cycle defects
Allergic reactions

Common adverse effects

Nausea and abdominal pain
Diarrhoea at doses above 6 g/day
Headache

PregnancyFDA C

FDA Category C. Safety of pharmacological doses in pregnancy has not been studied. In hepatic encephalopathy during pregnancy the hepatologist and obstetrician decide on LOLA.

Breastfeeding

Compatible. Ornithine is present in human milk and dietary protein. Therapeutic doses in a lactating woman with hepatic encephalopathy are assessed individually.

Calculate RID

Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.

Frequently asked

What is L-Ornithine used for?

L-Ornithine is evaluated for the following indications with varying evidence strength: Hepatic encephalopathy (evidence tier B), Weight loss (evidence tier D). See the full indication matrix with dosing and citations above on this page.

What are the side effects of L-Ornithine?

Common side effects of L-Ornithine (≥ 1 in 100): Nausea and abdominal pain, Diarrhoea at doses above 6 g/day, Headache. See the Safety section for uncommon and serious reactions.

Is L-Ornithine safe during pregnancy?

FDA category C. FDA Category C. Safety of pharmacological doses in pregnancy has not been studied. In hepatic encephalopathy during pregnancy the hepatologist and obstetrician decide on LOLA.

Is L-Ornithine compatible with breastfeeding?

Compatible. Ornithine is present in human milk and dietary protein. Therapeutic doses in a lactating woman with hepatic encephalopathy are assessed individually.

Who should not take L-Ornithine?

L-Ornithine is contraindicated in: Hypersensitivity to ornithine; Severe renal failure (creatinine above 3 mg/dL); Inherited urea cycle disorders. Full list in the Safety section.

Mechanism of action

Indications

Hepatic encephalopathy

Adjunct

Sources

Cochrane: L-ornithine L-aspartate for prevention and treatment of hepatic encephalopathy in people with cirrhosis (2018)

Safety

Contraindications

Hypersensitivity to ornithine
Severe renal failure (creatinine above 3 mg/dL)
Inherited urea cycle disorders

Serious adverse effects

Worsening hyperammonaemia in inherited urea cycle defects
Allergic reactions

Common adverse effects

Nausea and abdominal pain
Diarrhoea at doses above 6 g/day
Headache

PregnancyFDA C

FDA Category C. Safety of pharmacological doses in pregnancy has not been studied. In hepatic encephalopathy during pregnancy the hepatologist and obstetrician decide on LOLA.

Breastfeeding

Compatible. Ornithine is present in human milk and dietary protein. Therapeutic doses in a lactating woman with hepatic encephalopathy are assessed individually.

Calculate RID

Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.

Frequently asked

What is L-Ornithine used for?

What are the side effects of L-Ornithine?

Common side effects of L-Ornithine (≥ 1 in 100): Nausea and abdominal pain, Diarrhoea at doses above 6 g/day, Headache. See the Safety section for uncommon and serious reactions.

Is L-Ornithine safe during pregnancy?

FDA category C. FDA Category C. Safety of pharmacological doses in pregnancy has not been studied. In hepatic encephalopathy during pregnancy the hepatologist and obstetrician decide on LOLA.

Is L-Ornithine compatible with breastfeeding?

Compatible. Ornithine is present in human milk and dietary protein. Therapeutic doses in a lactating woman with hepatic encephalopathy are assessed individually.

Who should not take L-Ornithine?

L-Ornithine is contraindicated in: Hypersensitivity to ornithine; Severe renal failure (creatinine above 3 mg/dL); Inherited urea cycle disorders. Full list in the Safety section.