**6. Conclusions**

To determine to what extent the microbiome plays a role in the pathophysiology of ADHD, further studies are needed. We discussed several triggers that have been associated with ADHD, how these correlate with an altered microbial composition, and thus, how various microbes might act as possible biomarkers for ADHD. Further research, on the microbial composition of ADHD patients using large, well-diagnosed cohorts is needed in order to find future conclusive biomarkers and therapeutic methods to treat ADHD.

**Author Contributions:** Conceptualization, S.B.-L. and M.H.M.; Methodology, S.B.-L. and M.H.M.; Validation, M.H.M.; Formal Analysis, S.B.-L., and M.H.M.; Investigation, S.B.-L., and M.H.M., Resources, S.B.-L. and M.H.M.; Data curation, S.B.-L.; Writing—Original Draft Preparation, S.B.-L.; Writing—Review and Editing, S.B.-L. and M.H.M.; Visualization, S.B.-L.; Supervision, M.H.M.; Project Administration, M.H.M. and S.B.-L.

**Funding:** This research received no external funding.

**Acknowledgments:** We thank David Wolfer for helpful discussions and for critically reading this manuscript.

**Conflicts of Interest:** The authors declare no conflict of interest.
