Effects of 5-hydroxytryptophan on distinct types of depression: a systematic review and meta-analysis.

Abstract

Serotonergic dysfunction, including reduced central serotonin levels, is associated with different psychiatric syndromes, including depression. As a serotonin precursor, 5-hydroxytryptophan has long been used as a nonpharmacological treatment for depression. A systematic review and meta-analysis was conducted to determine the antidepressant effects of 5-hydroxytryptophan in depressed patients. MEDLINE (via PubMed) and Google Scholar were searched from inception to May 2018. Thirteen investigations were included in the systematic review (using PRISMA guidelines), and 7 in the full meta-analysis (pre-registered on PROSPERO: CRD42018104415). Analyses revealed a depression remission rate of 0.65 (95% confidence interval [CI], 0.55-0.78; remission rate [k] = 13), and this was confirmed by the questionnaire results, which revealed a large Hedges' g (1.11; 95%CI, 0.53-1.69). Methodological variability (in treatment duration, type of depression studied, experimental design, 5-hydroxytryptophan dosage) contributes to heterogeneity in the results (I2 = 76%, τ2 = 0.379). In addition, the OHAT (Office of Health Assessment and Translation risk of bias rating) tool suggested that, on the whole, current studies are relatively weak (few include placebo groups). Further trials should overcome these limitations by using placebo-controlled studies that include patients with well-defined depression diagnoses, along with strong characterization of psychological and physiological patient characteristics.