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Norden raises a potentially serious problem that may arise from the consumption of tryptophan-free amino acid mixtures. Tryptophan-free amino acid mixtures will cause a rapid but transient depletion of plasma tryptophan in humans, and this can indeed lead to a depressive relapse during the time that plasma tryptophan is low. Psychiatric patients taking antidepressant drugs should be warned about consumption of such amino acid mixtures without first consulting a physician.
However, there are several reasons why a depressive relapse after use of over-the-counter amino acid mixtures may not be very likely to occur. Tryptophan has not been removed from all nutritional supplements. The Food and Drug Administration is allowing the use of tryptophan in other forms (Paul David, regulatory management officer, Food and Drug Administration, oral communication, March 24,1992). Many nutritional supplements have bypassed the use of tryptophan by incorporating a source of protein (such as soy) that naturally contains
Delgado P, Charney DS, Price LH. Risk of Tryptophan Depletion Following Amino Acid Supplementation-Reply. Arch Gen Psychiatry. 1993;50(12):1000–1001. doi:10.1001/archpsyc.1993.01820240084011