What Is Ornithine & How Can It Benefit Endurance Performance?

We are all familiar with amino acids, like the BCAAs, that help with muscle repair. But did you know there are other amino acids that do not create proteins and serve other vital roles in the body besides helping you to recover. Ornithine, or L-Ornithine, is one of these amino acids and supplementing with it may provide both health and athletic performance benefits.  In this article we will discuss what L-Ornithine is, the benefits it can provide to athletes, proper dosage and timing, and if it is safe.

Fast Facts On Ornithine

  1. Ornithine is one of the amino acids that play a role in the Urea Cycle. This cycle helps rid our bodies of toxic ammonia by converting it to urea for excretion.
  2. Supplementing with ornithine helps rid our bodies of excess ammonia and can provide both health and athletic performance benefits.
  3. Standard dosing for l-ornithine is 2-6 grams daily.
  4. Ornithine HCL is the most bioavailable form of ornithine and the one used in most research studies.
  5. In higher doses ornithine may cause diarrhea.

What Is L-Ornithine?

Ornithine is one of the amino acids that play a role in the Urea Cycle (Citrulline and Arginine are the other two).  This cycle helps rid our bodies of toxic ammonia by converting it to urea for excretion. When supplemented, L-Ornithine appears to reduce ammonia levels and therefore may provide some unique health and athletic performance benefits.

Ornithine For Health

As it relates to health, Ornithine seems to be an effective supplement for individuals with a clinical liver condition or chronic cardiovascular disease. Both these conditions are characterized by high ammonia concentrations in the body and L-Ornithine helps the body get rid of this excess toxic compound.

Furthermore, Ornithine (when taken beforehand) may help after a heavy night of drinking alcohol and lessen the symptoms of a hangover.  Alcohol increases ammonia in the body while ornithine can reduce it.

What Is The Proper Dose Of L-Ornithine For Health?

Most research demonstrates that an effective dose of l-ornithine for health is 2-5 grams daily.

Ornithine For Athletic Performance

When athletes exercise, ammonia in skeletal muscle begins to accumulate and induces muscular fatigue.  This ammonia accumulation is exacerbated when endurance exercise goes over 45 minutes. Because Ornithine is able to decrease ammonia concentrations in the blood, it is effective at enhancing endurance performance especially as the duration of exercise increases.

What Is The Proper Dose Of L-Ornithine For Performance?

2 grams of Ornithine ingested 45-60 minutes before endurance exercise.

Research On Ornithine And Athletic Performance

A 2008 study conducted by Sugino et al. discovered that subjects who supplemented with 2 grams of ornithine 6 days prior to a cycle ergometer test (2 hours at 80% VO2 max) were able to reduce perceptions of fatigue by 52% compared to placebo.  Researchers also noted a decrease in serum ammonia concentrations in the subjects who supplemented with l-ornithine relative to placebo.

Another study conducted in 2010 by Demura et al. discovered that subjects who consumed ornithine hcl before an incremental, exhaustive bicycle ergometer test increased their ability to buffer ammonia accumulation both during and after exercise.

What Is The Best Form Of Ornithine?

The majority of research examining the benefits of ornithine have used ornithine hcl (hydrochloric acid). It is theorized that combining ornithine with an acid makes it more bioavailable in the body compared to free form l-ornithine.

Is Ornithine Safe/Are There Any Side Effects?

Ornithine appears to be a very safe supplement. However, in higher doses (above 6 grams), ornithine may cause diarrhea. This is especially true when combined with higher doses of arginine that can cause nitric oxide production in the colon.

The Bottom Line On L-Ornithine

Based on the available research, ornithine appears to be an effective supplement that can confer performance benefits in athletes. This is especially true for endurance athletes who may exercise strenuously for over 45 minutes. 2 grams of ornithine (as ornithine hcl) should be ingested 45-60 minutes before exercise to reduce ammonia accrual in the body.


Sugino, T., Shirai, T., Kajimoto, Y., & Kajimoto, O. (2008). L-ornithine supplementation attenuates physical fatigue in healthy volunteers by modulating lipid and amino acid metabolism. Nutrition research28(11), 738-743.

Demura, S., Yamada, T., Yamaji, S., Komatsu, M., & Morishita, K. (2010). The effect of L-ornithine hydrochloride ingestion on performance during incremental exhaustive ergometer bicycle exercise and ammonia metabolism during and after exercise. European journal of clinical nutrition64(10), 1166.