The Effects of 5-HTP and L-Theanine on Behavioral Stress Responses in Drosophila melanogaster

Millions of people are impacted by anxiety disorders; however, there is still limited scientific evidence and research regarding numerous over-the-counter supplements claiming they are effective for anxiety. Fruit flies, Drosophila melanogaster, share more than 60 percent of their disease-related genes with humans. Therefore, fruit flies can be used as an effective animal model for evaluating the behavioral aspects of stress reactions.

A critical gap in the existing literature is the lack of controlled, dose-dependent comparative evaluations of multiple dietary supplements on stress-related behavioral responses within a single experimental framework. This study investigated how varying dosages (2, 2.5, 3 ppm) of 5-HTP (5-hydroxytryptophan) and L-theanine (an amino acid naturally found in tea leaves) affected locomotor activity, thigmotaxis, and light startle response in Drosophila melanogaster. Six treatment groups and one control group (only received Drosophila food and water) were used to test the dietary supplements, 5-HTP and L-theanine, at three different concentrations.

Results showed clear dose-dependent effects from both the 5-HTP and L-theanine. As concentration increased, locomotor activity and light-startle response both decreased whereas thigmotaxis increased for both dietary supplements. However, L-theanine produced stronger effects than 5-HTP. The results support the use of Drosophila as a model organism for investigating the behavioral effects of both dietary supplements and provide a foundation for future research on stress-related neuromodulation.