Probiotics May Lift Your Mood in Just Two Weeks, Study Finds

The study, published in npj Mental Health Research, followed 88 healthy participants with no prior mental health diagnoses. Half of the participants received probiotics, while the other half took placebos. Over four weeks, the participants completed standard mental health questionnaires at the start and end of the study. In addition, they provided daily reports on their emotional states. This daily self-reporting proved crucial in detecting subtle emotional changes that traditional assessments often miss.

The results were striking. While improvements in mood were not immediately apparent, the probiotics started showing their beneficial effects around the two-week mark. This timing is comparable to how long it takes for antidepressants to begin showing signs of effectiveness. These results suggest that probiotics may influence emotional regulation through similar pathways as antidepressants, including the vagus nerve, which is the primary connection between the gut and the brain, and their anti-inflammatory effects.

Probiotics, also called good bacteria, are best known for supporting gut health. However, past research has suggested that they may offer more than just digestive benefits. They have been linked to improvements in immune function, reduced inflammation, and potential protection against various conditions such as obesity, osteoporosis, and gum disease. Additionally, a growing body of research has explored their role in mental health, with studies showing that probiotics may help alleviate symptoms of depression and anxiety.

Katerina V.-A. Johnson and Laura Steenbergen from Leiden University, Institute of Psychology, Leiden, The Netherlands, build on this foundation by providing more evidence that probiotics can positively impact mental health by reducing negative feelings and improving mood. Unlike many traditional studies that rely solely on pre- and post-intervention assessments, this study’s daily mood tracking revealed subtle emotional shifts that would likely have been overlooked by conventional methods. This suggests that daily self-reporting is a valuable tool in detecting the nuanced effects of probiotics on emotional regulation.

The study’s findings help resolve some of the inconsistencies in previous research, where the effects of probiotics on mental health have been mixed. By using a randomized, double-blind, placebo-controlled design, the researchers were able to offer more robust evidence that probiotics have a measurable impact on mood. While other significant changes were not observed, improving mood among probiotic users is a promising step forward in understanding the potential mental health benefits of gut bacteria.

Ultimately, this research highlights the role of probiotics in promoting mental well-being, especially in the general population. The ability to target specific individuals who may derive the greatest benefit from probiotics could lead to more personalized and effective mental health strategies in the future.

"With this new evidence, probiotics are emerging as a promising tool not only for gut health but also for supporting emotional and mental well-being, offering an accessible and natural alternative for those looking to boost their mood and reduce negative feelings," the authors concluded.

Reference:

Johnson, K. V., & Steenbergen, L. (2025). Probiotics reduce negative mood over time: The value of daily self-reports in detecting effects. Npj Mental Health Research, 4(1), 1-9. https://doi.org/10.1038/s44184-025-00123-z