Limited evidenceGut health

Lactobacillus Brevis

Best known as a GABA-producing species, which is why it is sold for calm and sleep. The human trials that exist are mostly dental, and the one mood study did not show better cognitive performance.

Evidence last reviewed: August 2026

What the science says

Oral and dental health Limited evidence
A double-blind, randomized, placebo-controlled trial of L. brevis CD2 in healthy adults reported improvements in oral health markers, and a separate trial found effects on caries-related variables in dental plaque. Small trials of one strain.
Mood and GABA Limited evidence
A double-blind, placebo-controlled crossover study of GABA-producing lactobacilli found a change in cognitive reactivity to negative mood without any improvement in cognitive performance. Bacterial GABA production in the gut has not been shown to raise brain GABA in humans.
Digestive symptoms Limited evidence
No adequately powered randomized trial has tested L. brevis alone for IBS, bloating or constipation.

Dosage & safety

Studied doseTrial doses vary by strain, roughly 1–10 billion CFU per day; CD2 oral studies used lozenges dissolved in the mouth.

SafetyWell tolerated. Do not rely on it for anxiety or insomnia in place of evidence-based treatment. Standard caution for live probiotics in severe immunosuppression or critical illness.

Scientific references

Levilactobacillus brevis CD2 as a multifaceted probiotic to preserve oral health: results of a double-blind, randomized, placebo-controlled trial in healthy adults
Altamura S, Lombardi F, Augello FR, Barone A, Giannoni M, Cinque B, Pietropaoli D — J Transl Med, 2025
The Probiotic Effects of Lactobacillus brevis CD2 on Caries Related Variables of Dental Plaque Biofilm
Campus G, Cagetti MG, Lehrkinder A, Alshabeeb A, Caimoni N, Lingström P — Int Dent J, 2025
Gaba-producing lactobacilli boost cognitive reactivity to negative mood without improving cognitive performance: A human Double-Blind Placebo-Controlled Cross-Over study
Casertano M, Dekker M, Valentino V, De Filippis F, Fogliano V, Ercolini D — Brain Behav Immun, 2024

Where to buy

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