Taking a specific amount of citrulline powder every day for a week can raise levels of certain amino acids in your blood, but it doesn’t change other important blood or urine markers like insulin or albumin.

A double-blind, placebo-controlled RCT in healthy adults (n≥30) receiving either oral citrulline (0.18 g/kg/day) or placebo for 7 days, with plasma amino acids (citrulline, arginine, ornithine) and biomarkers (albumin, transthyretin, insulin, IGF-1) measured at baseline, day 4, and day 7, and urinary nitrate collected over 24-hour periods at each time point.

A within-subject crossover trial in healthy adults where each participant receives citrulline (0.18 g/kg/day) and placebo in random order, separated by a 14-day washout, with plasma and urinary biomarkers measured at the end of each 7-day period to detect changes specific to citrulline intake.

A prospective cohort study in healthy adults where participants self-select into citrulline-supplemented (0.18 g/kg/day for 7 days) or non-supplemented groups, with biomarkers measured before and after the intervention period under controlled conditions.

A case-control study comparing plasma and urinary biomarker levels in healthy adults who recently took citrulline (0.18 g/kg/day for 7 days) versus those who did not, with retrospective confirmation of intake and timing.

A series of individual cases where healthy adults take citrulline (0.18 g/kg/day for 7 days) and have serial plasma and urinary biomarker measurements to document changes within each person.