Table 1.

Summary of studies testing the effects of probiotic supplements on mood. Effect on mood is indicated with: + for a positive effect on mood, − for a negative effect on mood, and / for no effect on mood. Abbreviations: LDB, Light Dark Box; SDT, Step Down Test; FST, Forced Swim Test; SPT, Sucrose Preference Test; PSS, Perceived Stress Scale; BAI, Beck Depression Inventory; BDI, Beck Anxiety Inventory; HADS, Hospital Anxiety and Depression scale; POMS, Profile of Mood State.

Subject, Study Design and Model	Probiotic	Dose and Administration	Treatment Duration	Effect on Mood		Reference
Animal Studies
Male AKR mice with parasite-induced (Trichuris muris) chronic gastrointestinal inflammation	Bifidobacterium longum NCC3001 and Lactobacillus rhamnosus NCC4007	Gavaged daily, dose not specified	10 days	Reduction in anxiety-like behaviors in the LDB	+	[29]
Immunodeficient (B and T cell-deficient) male and female Rag 1−/− mice	L. rhamnosus R0011 and Lactobacillus helveticus R0052	109 CFU/mL in drinking water daily	4 weeks	Probiotic supplement normalized deficits in anxiety in LDB tests	+	[38]
Male C57BL/6 mice with liver inflammation-induced sickness behavior and brain inflammation	Commercial mixture VSL#3: L. casei, L. plantarum, L. acidophilus and L. delbrueckii subsp. Bulgaricus, B. longum, B. breve and Bifidobacterium infantis, Streptococcus salivarius subsp. Thermophiles. Strains unspecified	1.7 billion bacteria/day, gavaged daily	10 days	Prevention of a decrease in social interaction	+	[37]
Male AKR mice with chemically induced colitis	B. longum NCC3001 -	100 µL of 1 × 1010 CFU	7 days	A probiotic supplementation reduced anxiety-like behavior in SDT, but only when the vagus nerve was intact	+/	[39]
Male Sprague Dawley Rats	B. bifidum W23, B. lactis W52, L. acidophilus W37, L. brevis W63, L. casei W56, L. salivarius W24, L. lactis W19, L. lactis W58	4.5 g (2.5 × 109 CFU/g) of freeze-dried powder in 30 mL of tap water per cage (2 rats) daily	10 weeks	A probiotic mix decreased depressive-like behavior in FST	+	[35]
Male Sprague Dawley rats following maternal separation stress	B. infantis 35624	1 × 1010 live bacterial cells/100 mL drinking water	55 days	A probiotic supplement ameriorated MSS induced depressive-like behavior in FST	+	[40]
A probiotic given alongside 3 weeks of restraint stress in male Sprague Dawley rats	L. helveticus ns8	109 CFU/mL live bacteria in drinking water	3 weeks	Probiotic ameliorated stress-induced depressive-like behavior in SPT, and anxiety like behavior in EPM	+	[41]
Male BALB/c mice	L. rhamnosus JB-1	109 CFU, gavaged daily	28 days	Decreased anxiety-like behaviors in the EPM	+	[36]
Male Sprague Dawley rats	L. casei 54-2-33	104 CFU/mL in drinking water	14 days	Increase in anxiety-like behavior in the OFT and no difference in anxiety-like behavior in the EPM	−	[42]
Male Sprague Dawley rats	B. infantis 35624	1 × 1010 live bacterial cells/100 mL drinking water	14 days	No decrease in depressive-like behaviors in FST	/	[43]
Human Studies
Healthy adult men	L. rhamnosus JB-1	109 CFU, probiotic capsule, daily	8 weeks	No reduction in subjective stress measure, depression or anxiety scores on the PSS, BAI or BDI scales or improve cognitive measures	/	[44]
Healthy men and women	L. helveticus R0052 and B. longum R0175	3 × 109 CFU probiotic capsule daily	30 days	Reduction in depression and anxiety scores (HADS). In a subset of people with low baseline urinary cortisol, the perceived stress scores were also reduced by the probiotic	+	[47,48]
Healthy men and women	B. bifidum W23, B. lactis W52, L. acidophilus W37, L. brevis W63, L. casei W56, L. salivarius W24, and Lactococcus lactis (W19 and W58)	2.5 × 109 CFU probiotic capsule daily	4 weeks	Reduction in participant’s cognitive reactivity to sad mood	+	[49]
Men and women with chronic fatigue syndrome	L. casei Shirota	8 × 109 CFU probiotic capsule daily	2 months	Improved anxiety (BAI) but not depressive (BDI) symptoms	+/	[50]
Healthy men and women	Milk drink containing probiotic L. casei Shirota	6.5 × 109 CFU in a milk drink		Improvement in mood in POMS only in those who already had low mood	+/	[51]
Men and women with irritable bowel syndrome	Yohgurt containing Lactobacillus paracasei, ssp. paracasei F19, L. acidophilus La5 and B. lactis Bb12 (Cultura; active)	5 × 107 cfu/mL × 200 mL milk drink, daily	8 weeks	The probiotic yoghurt drink did not improve mood scores in HADS	/	[45]
Men and women with diagnosed depression	B. bifidum, L. acidophilus, and L. casei (strains not specified)	L. acidophilus (2 × 109 CFU/g), L.casei (2 × 109 CFU/g), B. bifidum (2 × 109 CFU/g), amount not specified	8 weeks	Reduction in symptoms of depression I BDI, along with fasting plasma insulin, glutathione, and C-reactive protein	+	[46]