Twelve patients with obsessive—compulsive disorder were studied after the administration
of a mixture of amino acids devoid of tryptophan (TRP) or a mixture containing all the
essential amino acids, in a double-blind, crossover design. The TRP-free mixture caused a
marked depletion of plasma TRP. After TRP decrease, mean ratings of obsessions and
compulsions, measured by Visual Analogue Scales (VAS) ratings, did not worsen. In
contrast with other reports in literature, TRP depletion also failed to alter mood in our …