Review of: Dickerson F et al, Bipolar Disord 2018. doi:10.1111/bdi.12652 [Epub ahead of print]

Type of study: Randomized double-blind placebo-controlled trial

Probiotics, the so-called “good” bacteria in the gut flora, have become popular as a natural treatment for various disorders. They are taken as capsules or through food sources like yogurt, vinegar, and fermented foods. Of relevance to psychiatry, some have theorized the existence of a “gut-brain axis,” in which probiotics influence mood and behavior through the vagus nerve and the endocrine and immune systems. Probiotics have shown promise in small studies of anxiety, depression, cognition, and weight loss, and this trial tested whether a daily probiotic could lower the rate of rehospitalization after a manic episode.

The authors randomized 66 patients to receive either a probiotic or placebo as an adjunct to their usual medications after discharge from a hospital stay for mania. The probiotic capsule contained two bacterial strains that are found in breast milk and thought to modulate immune function: Bifidobacterium lactis bb-12 and Lactobacillus rhamnosus GG.

After 6 months, the rate of rehospitalization was 3 times lower in patients who took probiotics (8 of 33, 24%) compared to those taking placebo (24 of 33, 73%). However, probiotics had no effect on manic and depressive symptoms (measured monthly using the YMRS, BPRS, and MADRS scales). No significant side effects were reported in this study.

TCPR’s Take
The study is small and needs replication, and while probiotics apparently reduced rehospitalization, the lack of benefit for actual mood symptoms reduces our confidence in the results.

Probiotics have potential benefits for medical conditions that often accompany bipolar disorder, like metabolic and irritable bowel syndromes. On the other hand, they may not be safe for everyone. While we await further confirmation of their risks and benefits, these “healthy bacteria” should be avoided in people who are pregnant, immunocompromised, or at high risk of infection, where probiotics pose known risks. The specific strains used in this study have a good safety record in humans, and they are available on Amazon as USANA-108 probiotic sticks and Culturelle Baby Grow and Thrive liquid.