Taking a specific amino acid supplement called L-citrulline twice a day for a week can help improve a key balance in your blood that lets your body make more nitric oxide — a molecule that helps your blood vessels relax and work better.

A double-blind, placebo-controlled, parallel-group RCT in healthy adults with elevated ADMA (confirmed by baseline plasma measurement), where participants receive either 3 g L-citrulline twice daily or placebo for 7 days, with plasma L-arginine/ADMA ratio measured before and after intervention using standardized LC-MS/MS, and nitric oxide synthase substrate balance inferred from enzymatic activity assays.

A single-blind, randomized crossover trial in the same population, where each participant receives both L-citrulline (3 g twice daily) and placebo for 7 days each, separated by a 14-day washout, with plasma L-arginine/ADMA ratio measured at the end of each phase to assess within-subject change and confirm dose-response.

A prospective observational cohort study tracking healthy adults with elevated ADMA who self-select to take 3 g L-citrulline twice daily for 7 days, measuring plasma L-arginine/ADMA ratio before and after, with controls matched for baseline ADMA who do not supplement.

A case-control study comparing plasma L-arginine/ADMA ratios in individuals who have taken 3 g L-citrulline twice daily for 7 days (cases) versus those who have not (controls), matched for baseline ADMA levels and other covariates.

An in vitro study using human endothelial cells exposed to physiological concentrations of L-citrulline (equivalent to 3 g twice daily) to measure changes in intracellular L-arginine/ADMA ratio and nitric oxide synthase activity.