Abstract
Background and purpose:
Several studies have indicated that altered serotonergic neurotransmission may contribute to non-motor features commonly associated with Parkinson's disease (PD) such as apathy and depression. 5-hydroxytryptophan (5-HTP) is the intermediate metabolite of L-tryptophan in the production of serotonin. To date, there has been inconsistent research on the use of 5-HTP in PD. The purpose of this study was to compare the effects of 5-HTP with those of placebo on apathy and depressive symptoms in patients with PD.
Methods:
A single-center, randomized, double-blind placebo-controlled cross-over trial was employed; 25 individuals were subsequently enrolled into the study. Patients received placebo and 50 mg of 5-HTP daily over a period of 4 weeks. For the assessment of efficacy on depressive and apathy symptoms the Beck Depression Inventory-II (BDI-II), Hamilton Depression Rating Scale (HDRS) and Apathy Scale (AS) were respectively administered at screening, baseline and weeks 4, 8, 12 and 16. Primary efficacy outcomes were the comparison of 5-HTP to placebo in mean change from baseline to weeks 4, 8, 12 and 16 in total score on the AS, BDI-II and HDRS.
Results:
Repeated-measures analysis revealed a significant improvement of depressive symptoms during the 50-mg 5-HTP treatment compared with placebo as assessed by the HDRS. No effect of 5-HTP was seen on apathy symptoms assessed by the AS.
Conclusions:
This study provides preliminary evidence of clinical benefit of 5-HTP for treating depressive symptoms in PD. Larger studies with a longer treatment duration are needed to corroborate these early findings.
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