Evidence C · Moderate
Water-soluble
Chronic (weeks)
A classic combination of amino acids with distinct mechanisms: L-Arginine is a nitric oxide precursor (via NO synthase) and a substrate of the urea cycle; L-Ornithine is the "regenerator" of the urea cycle, responsible for ammonia clearance (NH₃) — which builds up during prolonged endurance and contributes to central fatigue.
Dose1 level teaspoon (3.1 g)
L-Arginine2.25 g per dose
L-Ornithine750 mg per dose
TimingFasted (morning or pre-sleep)
Why it makes sense for ultramarathon runners
- Ammonia clearance (Ornithine): in long races (4h+), muscles produce ammonia from amino acid breakdown. Ornithine before or after the race speeds up recycling via the urea cycle, reducing central fatigue.
- Recovery: arginine + ornithine pre-sleep may support tissue repair during the peak window of endogenous GH.
- Supplemental NO: although L-Citrulline/Nitrosigine is superior for NO (escaping the first-pass effect), high-dose arginine (2.25g) still contributes marginally.
- Endogenous creatine synthesis: arginine is one of the 3 amino acids in creatine synthesis (together with glycine and methionine).
Product in use: LE Arginine Ornithine Powder
Life Extension's Arginine Ornithine Powder is an unflavored powder:
- 2.25 g of L-Arginine HCl per teaspoon (3.1 g)
- 750 mg of L-Ornithine HCl per teaspoon
- 48 doses per 150 g bottle
- No additives (HCl is simply the stabilized form of the amino acid)
How to take (3 practical protocols)
- Focus on muscle recovery (most common): 1 teaspoon pre-sleep, fasted (≥2h after dinner). Takes advantage of the nighttime GH peak and the urea cycle's "free time".
- Focus on endurance / ammonia clearance: 1 teaspoon 60–90 min before long workouts (extended Z2 or runs >2h).
- Focus on protein synthesis: 1 teaspoon in the morning, fasted, 30 min before breakfast.
⚠️ Take fasted: arginine absorption competes with other amino acids for the same intestinal transporter (the y+L system). Taking it with a protein-rich meal drastically reduces the plasma peak.
Difference vs. NitroVasc/Nitrosigine
NitroVasc Boost (Nitrosigine®) and LE Arginine Ornithine Powder act on related pathways but are not redundant:
- NitroVasc: acute, pre-workout, focused on vasodilation and O₂ cost.
- Arginine+Ornithine: chronic, fasted, focused on recovery and ammonia clearance.
- They coexist well — using NitroVasc pre-workout and Arg+Orn pre-sleep causes no adverse interaction.
Evidence limitations
- NO via Arginine: poorly effective in healthy humans due to the hepatic "first pass" (Citrulline is better).
- Endogenous GH: oral doses >5g of arginine transiently raise GH, but the effect is abolished during exercise.
- Direct performance: modest to nonexistent effect in trained individuals.
- Subjective recovery (RPE, fatigue): stronger evidence in endurance.