**4. Conclusions**

Cleaning up the gut microbiota by transplanting a totally new human gut microbiota in one shot, which is referred to as FMT, is likely to strongly improve the efficacy and maintains the effect over time. The safety and acceptability have been recently improved with capsule administration that should be evaluated in future clinical trials for the treatment of major depression and schizophrenia. Future trials should confirm the effectiveness and identify responder profiles in the context of personalized medicine.

**Author Contributions:** Conceptualization, G.B.F., J.-C.L. and L.B.; methodology, G.B.F.; resources, G.B.F.; data curation, G.B.F.; writing—original draft preparation, G.B.F., J.-C.L. and L.B.; writing—review and editing, G.B.F., J.-C.L., L.B., S.H., C.L., T.K., P.-L.S.D.V., P.-M.L., P.A., E.G.; supervision L.B.; funding acquisition, G.B.F. and L.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was funded by Hôpitaux Universitaires de Marseille (HUM), grant number AORC-2018.

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