We have previously reported that dietary supplementation with up to 5.0 g/d of l-tryptophan (l-Trp) for 21 d has no adverse effects, judging from the levels of general blood variables, in healthy women. We performed a randomized, double-blind, placebo-controlled, crossover intervention study in 17 apparently healthy Japanese women. The subjects were randomly assigned to receive a placebo (0 g/d) or 1.0, 2.0, 3.0, 4.0, or 5.0 g/d of l-Trp for 21 d each with a 5-wk washout period between trials.

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... e examined the 24-h urine profiles on days 21 (1 d before starting l-Trp), 7, 14, and 21 to determine whether administration of l-Trp at doses of up to 5.0 g/d affects time-dependent urinary excretion of l-Trp or its metabolites in healthy women. The urinary excretion of l-Trp, kynurenic acid, 3-hydroxykynurenine, xanthurenic acid, 3-hydroxyanthranilic acid, quinolinic acid, N 1 -methylnicotinamide, N 1 -methyl-2-pyridone-5-carboxamide, and N 1 -methyl-4-pyridone-3-carboxamide increased in an l-Trp dose-dependent manner on day 7. The amount of urinary excretion of these compounds was unchanged on days 14 and 21. The urinary excretion of serotonin, 5-hydroxyindole-3-acetic acid, 2-oxoadipic acid, and nicotinamide was unaffected by l-Trp at any of the doses tested. l-Trp doses had weak effects on the urinary excretion of kynurenine and anthranilic acid. Based on these findings, we conclude that there are no time-dependent effects of l-Trp administration in urinary excretion of l-Trp metabolites. Additionally, l-Trp and its metabolites do not accumulate in the body.