Abstract
Context:
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.
Objective:
A systematic review and meta-analysis was conducted to determine the antidepressant effects of 5-hydroxytryptophan in depressed patients.
Data sources:
MEDLINE (via PubMed) and Google Scholar were searched from inception to May 2018.
Data extraction:
Thirteen investigations were included in the systematic review (using PRISMA guidelines), and 7 in the full meta-analysis (pre-registered on PROSPERO: CRD42018104415).
Data analysis:
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).
Conclusion:
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.
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