Antidepressants as Potential Antimicrobials: Current Evidence, Challenges, and Implications for Antimicrobial Resistance

Background/Objectives: Antimicrobial resistance (AMR) is a major global health threat that has outpaced the development of new antibiotics. Drug repurposing has emerged as a promising strategy for identifying alternative antimicrobial therapies. Antidepressants have attracted interest because experimental studies suggest they possess off-target antimicrobial activity, although growing evidence indicates they may also promote antimicrobial resistance. This review critically examines both the therapeutic potential and risks of antidepressant–microbial interactions. Methods: A structured narrative review was conducted using literature identified from major biomedical databases. Experimental, animal, microbiome, environmental, and clinical studies were synthesized according to antidepressant class, antimicrobial mechanisms, interactions with conventional antibiotics, microbiome modulation, and antimicrobial resistance. Results: Experimental evidence demonstrates that several antidepressants inhibit bacterial and fungal pathogens through mechanisms including membrane disruption, oxidative stress induction, efflux pump inhibition, and biofilm interference. Some agents also enhance the activity of conventional antibiotics. However, current evidence is largely preclinical. Multiple studies indicate that antidepressants may also promote antimicrobial resistance through reactive oxygen species-mediated mutagenesis, efflux pump activation, horizontal gene transfer, microbiome dysbiosis, and environmental exposure. Conclusions: Antidepressants represent both a promising drug-repurposing opportunity and a potential contributor to antimicrobial resistance. Although their antimicrobial properties are encouraging, current evidence remains predominantly preclinical, and clinically effective and safe antimicrobial dosing has not been established. At present, their antimicrobial use should be regarded as proof-of-concept rather than a clinically validated therapeutic strategy. Further pharmacokinetic, pharmacodynamic, animal, and clinical studies are required before routine antimicrobial application can be considered.