The present invention relates to a method for treating, ameliorating, reversing and/or preventing autism or an autism spectrum disorder (ASD) via the administration of a formulation, a pharmaceutical preparation or a pharmaceutical composition comprising or consisting of: (a) a rifaximin (optionally a XIFAXAN, XIFAXANTA or NORMIXT), an extended intestinal release (EIR) rifaximin, a rifamycin derivative, a rifampicin (or rifampin) (optionally RIFADIN), a rifabutin (optionally MYCOBUTIN), a rifapentine (optionally PRIFTIN), a rifalazil, a bicozamycin, or a mixture or combination thereof, or (b) a rifaximin (optionally a XIFAXAN, XIFAXANTA or NORMIX) and at least one additional antimicrobial or antibiotic agent, wherein optionally the at least one additional antimicrobial or antibiotic agent comprises a vancomycin, a metronidazole (optionally FLAGYLTM, METROTM), a tinidazole (optionally FASIGYN, SIMPLOTAN, TINDAMAX) or a combination thereof
