A new field of research suggests that the gut microbiome may influence mood, mental health, and the nervous system's vitality. But is the supplement market way ahead of the evidence?

What are psychobiotics?

“Psychobiotics refer to probiotics that, when ingested in appropriate amounts, have a benefit to the brain and mental health,” explains Philip Burnet, associate professor in the department of psychiatry at the University of Oxford.

“We’ve proposed adding prebiotics​—foods or their components that feed beneficial bacteria already in the gut—to that list.” (Most prebiotics are indigestible carbohydrates like fiber.)

But so far, the evidence that any psychobiotics work is scanty. And some mood supplements—like Lifted Mood Boosting Probiotic and Renew Life Mood & Stress Probiotic—disclose their probiotics’ genus and species, but not the strains, so it’s impossible to know what they contain.

That leaves only a few strains that have been tested on mood. For example:


Garden of Life probiotics

“Promotes emotional well-being & relaxation,” reads the label of Garden of Life’s Mood+. The supplement contains Lactobacillus helveticus R0052 and Bifidobacterium longum R0175. (The label lists 14 other bacteria, but doesn’t identify their strains.)

Do those two popular strains work?

Only one (company-funded) study has tested them in people with what the researchers called “low mood.” Among 79 New Zealanders who had some symptoms of depression but weren’t on antidepressants, those who took the probiotic for two months fared no better than the placebo takers. (Somehow, Garden of Life’s website forgot to mention those results.)

In people without mood disorders, a handful of small studies—nearly all industry-funded—haven’t found much.

For example, in one study of questionable quality, 55 French adults were randomly assigned to take the two strains or a placebo. After a month, the probiotic takers reported a greater drop in only 5 out of 20 scores of depression, anxiety, stress, and coping ability than the placebo takers. But it’s not clear that those differences translate to “emotional well-being & relaxation.”

Other probiotics have come up empty. For example, Lactobacillus rhamnosus JB-1 reduced anxiety in mice. But when John Kelly, a lecturer in clinical psychiatry at Trinity College Dublin, randomly assigned 29 men without mood disorders to take a placebo or L. rhamnosus JB-1 for a month each, he found no effect on mood, anxiety, stress, or sleep.

“There’s a potential for probiotics to improve mental health, but the small studies haven’t been followed up with larger, better studies,” says Gregor Reid, professor of microbiology and immunology at Western University in Ontario. “Researchers aren’t taking the next step.”


“You can’t bottle feelings like this, but they are available in a sachet,” says the British ad for Bimuno. “Experts have shown that a healthy gut can help you feel good.”

Bimuno contains galacto-oligosaccharides. They’re chains of two to five sugar units (saccharides) that our digestive enzymes can’t break down, so they end up in the large intestine, where bacteria feed on them. That makes galacto-oligosaccharides a prebiotic.

“Unlike probiotics that contain just a few strains of bacteria, prebiotics feed and amplify many strains of your gut bacteria,” Burnet explains.

Only a few studies have looked at Bimuno’s effect on mood.

In a small trial funded by the company, Burnet randomly assigned 45 adults without mood disorders to take 5½ grams of Bimuno, a second prebiotic, or a placebo every day.

“We found that three-week administration of Bimuno didn’t change people’s mood,” says Burnet. “But it did affect one of the mechanisms that underlie mood.”

That is, people who took Bimuno tended to focus for 20 milliseconds longer on positive than on negative words compared to the placebo takers.

Would that lead them to “feel good” over time? Seems like a stretch.

Few studies have tested other prebiotics on people. And even if future research finds that prebiotics can lift your mood, they’ll never be a substitute for a healthy diet.

“Some people want to sprinkle a prebiotic supplement on their burger and fries and say that they’re healthy,” says Burnet. “But you’re better off eating a diet rich in many types of fiber.”

And don’t expect psychobiotics to replace antidepressants or other medications for mood disorders, he adds.

“Maybe psychobiotics will make drugs work better for some people. But that hasn’t been shown yet.”