Use of probiotics to benefit mood is a recent advancement in the scientific literature, first proposed in 2005 when researchers suggested its use as an adjuvant treatment (add-on treatment) to standard care for major depressive disorder.1 In 2013, scientists defined psychobiotic as, “a live organism that, when ingested in adequate amounts, produces a health benefit in patients suffering from psychiatric illness,” recommending probiotics as a novel class of psychotropic (mind-altering) treatment.2 Probiotics have been found to act as delivery vehicles for neuroactive compounds (compounds that stimulate the nervous system),3 and certain probiotic strains actually secrete neuroactive compounds.4,5

In animal models the probiotic Bifidobacterium infantis was found to increase the serotonin precursor tryptophan.6 Serotonin is the feel-good hormone, and many antidepressant medications work by increasing the availability of serotonin. Might probiotics one day fill the role of antidepressant? Time will tell. So far the studies indicate that it’s a good possibility. In another animal model, Bifidobacterium infantis was found to normalize immune response, reverse negative behavioral effects, and restore norepinephrine levels induced by stress.7 Lactobacillus rhamnosus has been found to reduce anxiety and alter expression of GABA (gamma-aminobutyric acid) receptors in another animal model.8 GABA is a calming neurotransmitter that has a counterbalancing effect to anxiety.

Human studies have also found benefit for probiotics on mood. In one study, individuals who took a combination of the probiotics Lactobacillus helveticus and Bifidobacterium longum for 30 days experienced reduced psychological distress and decreased cortisol levels (cortisol is released under stress) when compared to those who took placebo.9 Another human study found that healthy individuals who consumed a probiotic yogurt for three weeks and who had the lowest mood at the beginning of the study reported that they were happy rather than depressed after taking the probiotic.10 And in a study of patients with chronic fatigue syndrome, those taking Lactobacillus casei three times daily for two months experienced an improvement in anxiety when compared to those taking placebo.11

Also interesting to note, similar to antibiotics, antipsychotic medications have been found to alter the gut microbial balance by decreasing the amount of Actinobacteria (of which Bifidobacterium is a member) and Proteobacteria and increasing the number of Firmicutes.12 Likely not coincident, these individuals also gained weight—increases of Firmicutes have been found to be associated with weight gain.

The gut-brain connection is very interesting. As we continue to learn more about how our gut microbes affect mood, it is clear that probiotics—or psychobiotics as these researchers have termed them—will play an important role in managing or possibly even preventing mood disorders. I’ll keep you posted as we learn more.


  1. Logan AC, Katzman M, “Major depressive disorder: probiotics may be an adjuvant therapy.” Med Hypotheses. 2005;64(3):533-8.
  2. Dinan TG, Stanton C, and Cryan JF, “Psychobiotics: a novel class of psychotropic.” Biol Psychiatry. 2013 Nov 15;74(10):720-6.
  3. Lyte M, “Probiotics function mechanistically as delivery vehicles for neuroactive compounds: Microbial endocrinology in the design and use of probiotics.” Bioessays. 2011 Aug;33(8):574-81.
  4. Schousboe A, Waagepetersen HS, “GABA: homeostatic and pharmacological aspects.” Prog Brain Res. 2007;160:9-19.
  5. Roshchina VV, “Evolutionary Considerations of Neurotransmitters in Microbial, Plant, and Animal Cells.” In: Lyte M, Freestone PPE, editors. Microbial Endocrinology:Interkingdom Signaling in Infectious Disease and Health. New York: Springer, 17–52.
  6. Desbonnet L, Garret L, Clarke G, et al., “The probiotic Bifidobacteria infantis: An assessment of potential antidepressant properties in the rat.” J Psychiatr Res. 2008 Dec;43(2):164-74.
  7. Desbonnet L, Garret L, Clarke G, et al., “Effects of the probiotic Bifidobacterium infantis in the maternal separation model of depression.” Neuroscience. 2010 Nov 10;170(4):1179-88.
  8. Bravo JA, Forsythe P, Chew MV, et al., “Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve.” Proc Natl Acad Sci USA. 2011 Sep 20;108(38):16050-5.
  9. Messaoudi M, “Assessment of psychotropic-like properties of a probiotic formulation (Lactobacillus helveticus R0052 and Bifidobacterium longum R0175) in rats and human subjects.”
  10. Benton D, Williams C, Brown A, “Impact of consuming a milk drink containing a probiotic on mood and cognition.” Eur J Clin Nutr. 2007 Mar;61(3):355-61.
  11. Rao AV, Bested AC, Beaulne TM, et al., “A randomized, double-blind, placebo-controlled pilot study of a probiotic in emotional symptoms of chronic fatigue syndrome.” Gut Pathog. 2009 Mar 19;1(1):6.Davey KJ, O’Mahoney SM, Schellekens H, et al., “Gender-dependent consequences of chronic olanzapine in the rat: effects on body weight, inflammatory, metabolic and microbiota parameters.” Psychopharmacology (Berl). 2012 May;221(1):155-69.
  12. K.J. Davey, S.M. O’Mahoney, H. Schellekens, et al., “Gender-dependednt consequences of chronic olanzapine in the rat: effects on body weight, inflammatory, metabolic and microbiota parameters.” Psychopharmacology 221, no. 1 (May 2012):155–69.