## 4 Discussion  
The growing interest in non-pharmacological treatments for stress and related conditions has positioned psychobiotics and adaptogens as promising alternative interventions. This systematic review assesses their efficacy in alleviating stress-related psychophysiological symptoms, with particular attention to measurable improvements in stress and anxiety outcomes. It also explores which specific bacterial strains and herbal compounds are most consistently associated with beneficial effects, contributing to a more nuanced understanding of their therapeutic potential. A distinctive strength of this review lies in its dual examination of both psychobiotics and adaptogens--two emerging but often separately studied approaches--which allows for a broader perspective on microbiota- and plant-based strategies for stress regulation. This comprehensive scope contributes to a more integrated understanding of their potential benefits and limitations. As highlighted in the review by [PERSON] et al. [94], psychobiotics have demonstrated beneficial effects in addressing stress and anxiety in both animal and human studies, improving psychological and neurochemical profiles. Specifically, animal studies have provided compelling evidence for the potential of psychobiotics to modulate behavior and brain function through gut-brain axis mechanisms. Thus, chronic administration of specific strains such as _Bif. longum_ 1714 and _L. rhamnus_ JB-1 has been shown to reduce anxiety-like behaviors and improve stress responses in mice, including lowering corticosterone levels and enhancing performance in behavioral tests such as the elevated plus maze and forced swim test. On the other side, _L. helevicus_ NS8 and _L. plantarum_ have demonstrated effects on increasing neurotransmitter levels, including dopamine and serotonin in brain regions like the prefrontal cortex. In our systematic review, nine of the included studies reported positive treatment effects, showing significant improvements in stress biomarkers, anxiety-related symptoms, and self-perceived stress [71; 72; 73; 75; 78; 79; 84; 85; 86], suggesting a potential regulatory role of psychobiotics in stress response. Regarding the specific psychobiotic strains used in studies reporting positive effects, a diverse range of formulations was observed, including multi-strain probiotics and psychobiotic-enriched diets. However, most of the studies reviewed focused on strains from _Bif._ and _L._ families, which predominantly exhibited beneficial outcomes [71; 73; 75; 78; 79; 85]. This suggests that strains within these families may be particularly effective in mitigating stress and improving psychological well-being. These psychobiotics have also been consistently linked to reduced gastrointestinal discomfort and improved mental health outcomes, aligning with findings from [PERSON] et al. [45]. The effectiveness of psychobiotics for stress reduction varies considerably across the literature [47; 49; 51; 52] as well as in the studies analyzed in this review, with nearly half reporting no significant improvements in stress-related outcomes. For instance, _Bif. Breve_, _L. gasseri_, and _L. paracasei_[75; 78; 79; 86] have been associated with reductions in cortisol levels and self-reported stress, highlighting their potential utility in stress management. Additionally, _B. longum_ 1714 has been demonstrated to alleviate anxiety symptoms in human studies [39] and has shown to reduce salivary cortisol output and perceived stress levels [71], while another study did not show any effects [76]. Similarly, _L. plantarum_ PS128(tm) significantly reduced cortisol levels, self-perceived stress, and both trait and state anxiety in individuals experiencing high stress [85]. In contrast, _L. plantarum_ 299v did not produce any significant changes in patients diagnosed with major depression [81]. It is worth noting that although previous research has provided growing evidence of the positive effects of psychobiotics on mood-related disorders [36; 95], the mechanisms of action remain unclear.