Safe Serotonin Levels

Q I read your article “5-HTP Facts and Fiction,” and was wondering … you say that the blood serotonin levels that cause heart problems from carcinoid tumors are far higher than can be achieved by supplementing with 5-HTP. My question is, by how much?

DAIMON, Quebec

A A lot has been learned about carcinoid tumors in the last 10 years. Yet there is no research implicating either 5-HTP or tryptophan ingestion in the generation of these tumors. What is know is that carcinoid tumors cause an alteration in the metabolism of tryptophan and an increased synthesis of serotonin, producing high 5-HIAA (a serotonin metabolite) urinary concentrations.1

Furthermore, patients suffering from a metastatic carcinoid tumor demonstrate irritability, aggression, and lack of impulse control, conditions associated with low levels of plasma tryptophan and presumably with low brain serotonin function. In rats, researchers have shown that a diet of low tryptophan results in higher stress responses and higher corticosterone production.2 In the same study, in humans suffering from metastatic carcinoid disease, the cerebral access of plasma tryptophan was impaired, thus rendering cerebral serotonin neurotransmission suboptimal and leading to hypercortisolism. This provides further support that low serotonergic function is a risk for developing stress-associated psychopathology.


  1. Lionetto L, Lostia AM, Stigliano A, Cardelli P, Simmaco M. HPLC-mass spectrometry method for quantitative detection of neuroendocrine tumor markers: vanillylmandelic acid, homovanillic acid and 5-hydroxyindoleacetic acid. Clin Chim Acta 2008 Dec;398(1-2):53-6.
  2. Tanke MA, Kema IP, Dijck-Brouwer J, Doornbos B, De Vries EG, Korf J. Low plasma tryptophan in carcinoid patients is associated with increased urinary cortisol excretion. Psychoneuroendocrinology 2008 Oct;33(9):1297-301.

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