Taking L-arginine pills in these amounts doesn’t raise the levels of L-arginine or related molecules in your blood or urine, because your body breaks them down too quickly before they can get into your system.

In healthy adult participants, compare plasma L-arginine, urinary nitrate, and cGMP levels after 7 days of oral L-arginine (1.6 g twice daily) versus placebo and versus another 7-day period of L-arginine (1.0 g three times daily), with washout periods between arms, measuring outcomes via standardized blood and urine assays.

Compare changes in plasma L-arginine, urinary nitrate, and cGMP over 14 days in healthy adults receiving either L-arginine 1.6 g twice daily, L-arginine 1.0 g three times daily, or placebo, with baseline and endpoint measurements using validated assays.

Track the absorption, distribution, and presystemic metabolism of orally administered L-arginine using stable isotope-labeled L-arginine to quantify how much reaches systemic circulation versus is metabolized in the gut or liver.

Measure plasma and urinary biomarkers in healthy adults self-reporting daily L-arginine intake at 1.6 g BID or 1.0 g TID over 4 weeks, comparing to non-supplementing controls.

Demonstrate that L-arginine is extensively metabolized in human intestinal cells and hepatocytes before entering systemic circulation, using tissue explants or cell lines exposed to physiologic concentrations.