## 4 Discussion
Notably, studies reporting significant stress reduction effects were primarily conducted in participants experiencing high baseline stress levels or engaging in unhealthy dietary habits [40; 72; 73; 78; 79; 84; 85; 86], like the findings in the study by [PERSON] et al. [40], which also observed greater benefits of psychobiotic intervention in individuals with elevated stress levels. This suggests that initial gut health may play a crucial role in mediating the effectiveness of psychobiotic interventions. Participants with gut microbiota imbalances or heightened stress levels at baseline appeared to benefit the most, showing improvements in stress hormone levels, anxiety symptoms, and self-perceived stress. Conversely, studies conducted in healthy or low-stress populations often yielded null results, implying that the therapeutic potential of psychobiotics may depend on pre-existing gut dysbiosis or stress-related imbalances. In relation to adaptogens, the vast majority of studies have demonstrated significant reductions in stress biomarkers, anxiety symptoms, and self-perceived stress [87; 88; 89; 90]. In the systematic review by [PERSON] et al. [55], which analyzed 56 human and animal studies on adaptogens, it was concluded that natural adaptogens enhance the body's ability to resist stress-induced changes, providing several beneficial effects. Similarly, our systematic review found homogeneous results, with most studies reporting a significant decrease in stress biomarkers, anxiety symptoms, and/or self-perceived stress following adaptogen treatment [87; 88; 89; 90]. Regarding participant characteristics in studies showing positive effects, most included healthy individuals without any significant medical conditions [88; 89; 90], while a smaller number focused on participants experiencing high levels of stress or undergoing stressful situations [87; 91]. Among adaptogens, _W. somifera_ emerges as the most frequently studied and effective one, with its consistent efficacy across varying baseline stress levels highlighting its broad applicability. These findings align with previous research demonstrating its positive effects in reducing stress and cortisol levels [61; 87; 96]. Therefore, it can be hypothesized that _W. somifera_ plays a particularly beneficial role in the treatment of stress and anxiety symptoms. While the precise mechanisms of action of adaptogens are not yet fully understood, evidence suggests that Ashwagandha root extract influences the HPA axis and key stress mediators, leading to modulations in cortisol levels [89; 97]. These results are similar to those found in animal studies; in this sense, reduction in anxiety and stress indicators show the following: In domestic dogs, Ashwagandha root extract significantly reduced stress-related signs, including a decrease in urine cortisol-to-creating ratio and improvements in fear and anxiety domains as measured by behavioral assessments [98]. Similarly, in Wistarrats, Ashwagandha demonstrated significant anxiolytic effects, improving anxiety- and depression-like behaviors and reducing stress hormones such as cortisol [99]. Regarding limitations, this review highlights several areas for improvement in future research. One of the primary challenges is the heterogeneity in psychobiotic substances and adaptogen formulations as well as the variability in participant characteristics. These factors complicate direct comparisons and limit the generalizability of findings. Additionally, the small sample sizes across studies reduce statistical power and compromise the reliability of the results, emphasizing the need for larger and more diverse cohorts. Another key limitation is the lack of long-term follow-up assessments. While many studies report reductions in stress biomarkers and self-reported stress levels during intervention periods, it remains unclear whether these benefits are sustained after treatment discontinuation.