L-ornithine is a non-essential amino acid, which your body can make from arginine. It’s found in very low concentrations in food and the highest natural source is freshwater clams.
L-ornithine administration increases ketone bodies and free fatty acids and promotes lipid metabolism (fat oxidation), as well as lowers blood ammonia levels by activating the urea cycle and increases ammonia detoxification from the liver. (1, 2, 3)
L-ornithine is not an amino acid that is incorporated into proteins, and doesn’t aid directly in muscle protein synthesis. (4) The release in growth hormone (GH) that it causes, stimulates muscle protein synthesis (MPS), so ornithine acts indirectly on muscle.
Anti-cortisol, anti-fatigue, pro-sleep
400mg/day of l-ornithine is shown to reduce stress, relieve fatigue, promote sleep and lower cortisol and anger. (5, 6) This is possibly because it binds with GABA receptors. Even as low as 200mg with 100mg caffeine (1 cup) is enough to improve mood and relieve fatigue. Workers report more energy, vigor, and willingness to work even late in the day, which displays its long-lasting effect, as well as a synergistic effect with caffeine. Caffeine is known to increase dopamine which has a positive effect on mood.
L-ornithine also significantly reduced the subjective feeling of fatigue during and after exercise. (7)
Growth hormone and muscle gains
Ornithine alone and in combination with arginine increases GH and IGF-1 and lowers IGFBP3. (8, 9)
Taking 2g each of arginine and ornithine pre-workout has been shown to result in significantly greater gains in total strength and lean body mass. Urinary hydroxyproline (an indicator of muscle catabolism) was also significantly lower post-workout. These changes were evident after just 5 weeks of high-intensity strength training. (8) With aerobic exercise, ornithine doesn’t seem to improve exercise, but does increase the ability to buffer ammonia. (8)
Extras and dosing
Ornithine increases wound healing in mice by enhancing wound breaking strength and collagen deposition. (10)
For improving energy during the day and for better sleep I recommend starting at 500mg in the morning and 500mg before bed.
If you have some serious ammonia buildup issues, take 2g each of citrulline, arginine and ornithine before bed each night.
If serious muscle gains are desired, take 2.5g pre-workout and 5g before bed each day. Cycle this routine 5 days on 2 days off.