Specific amino acids, including arginine, lysine, and ornithine, can stimulate growth hormone release.  Some people increase ornithine consumption before exercise to increase growth hormone release and increase muscle mass and strength.

Oral amino acids in large doses are likely to cause stomach discomfort and diarrhea. This is why some users prefer an injectable over oral amino acids.

Intensive exercise also increases growth hormone release. In one study, increased ornithine before strenuous exercise increased growth hormone more than placebo.

L-ornithine does not make you sleepy, but it can reduce stress. In one study, L-ornithine consumption reduced cortisol levels, a marker for stress, and improved perceived mood and sleep quality. Participants also reported less anger and reduced fatigue.

In a clinical study, participants reported feeling less fatigue, hostility, and confusion after alcohol consumption when they took 400 mg of ornithine.

Taking 400 mg of ornithine improved mood and reduced salivary cortisol (a stress hormone) after alcohol consumption.

The study was small, but only enrolled “flushers” people who experienced negative side effects to alcohol consumption.

L-citrulline is converted to L-arginine in the body. L-arginine increases nitric oxide, a small molecule that relaxes smooth muscle lining blood vessels and increases blood flow.

Oral ED medications also increase nitric oxide. These medications increase blood flow into the penis, filling the corpora cavernosa, increasing pressure and producing an erection.

In one study, researchers found that supplementing with L-citrulline increased PGC‐1α levels, which resulted in increased skeletal muscle mass and prolonged time to muscle exhaustion.

In another study, cyclists who supplemented with L-citrulline had shorter race completion times and reported less muscle fatigue and better concentration after the race.

Both arginine and citrulline increase the production of nitric oxide, which increases blood flow into the muscle.  However, oral arginine intake is subject to first-pass and systemic metabolism, which means less is available in your body to impact nitric oxide production. Citrulline is not subject to first-pass metabolism and, therefore, more effectively increases nitric oxide.

In a randomized, controlled study, adding L-arginine to sildenafil improved erectile function more than sildenafil alone.

Both L-arginine and sildenafil increase nitric oxide production. Nitric oxide relaxes the smooth muscle lining blood vessels increasing blood flow into the penis, producing an erection.

The combination increased the rate of gastric upset, but no other side effects were increased in number or severity.

Both sildenafil and arginine can reduce blood pressure. Talk to your doctor before combining arginine and sildenafil.

Potential side effects from arginine supplementation are rare but may include:

• Stomach discomfort, nausea, stomach cramps
• Changes in stools
• Low blood pressure
• Fainting
• Changes in blood electrolytes levels
• Low back pain
• Flushing
• Headaches
• Numbness
• Restless legs
• Venous irritation and tissue death around the injection site
• Increased blood glucose levels
• Increased potassium levels