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Psychobiotics: A Revolution in Psychiatry

Psychobiotics are microbes that lift your mood. Psychiatry needs them now.

What are psychobiotics? Despite their somewhat sinister-sounding name, psychobiotics are microbes that can lift your mood and decrease anxiety. The word was coined by Psychiatrist and researcher Dr. Ted Dinan and colleague John Cryan, Chair of Anatomy and Neuroscience at University College Cork, in Ireland. These prolific investigators have pioneered research into the gut-brain axis, along with other scientists from fields as disparate as microbiology, immunology, psychiatry, endocrinology, gastroenterology, and neurology. Researching the gut-brain axis requires a surprising diversity of disciplines.

Yogurt can be a source of psychobiotics.
Source: Nensuria/iStock

What is depression?

There are many reasons for people to feel depressed or anxious. Bereavement, for one, often leads people into depression. That is normal and expected, as long as it doesn’t linger too long.

There are many treatments for people with depression, including psychoactive drugs that attempt to rebalance the neurotransmitters used by brain cells to communicate with each other. These drugs tend to target dopamine and serotonin centers of the brain, because these areas of the brain seem to be involved in happiness and motivation. There is also cognitive behavioral therapy, which has had a great track record for many people.

But there is a growing appreciation for the damage that can result from a “leaky gut”, a phenomenon that allows toxins and bacteria to enter the bloodstream. Once that happens, the heart diligently pumps these pathogens to every organ in the body, including the brain.

There is a barricade, called the blood-brain barrier, that keeps pathogens out of the brain, but we now have evidence that this barrier can be breached, creating a “leaky brain” analogous to the leaky gut. In extreme cases, this leads to brain inflammation that can deeply disturb the affected person, causing anxiety, confusion, hallucinations and sharp personality changes.

But inflammation can also lead to garden-variety depression and anxiety. It is not a small problem. The comorbidity of depression and gut disease can be as high as 75%. It looks similar to “ordinary” depression, but the cause lies in the gut, not the brain. This is the gut-brain axis, which initially popped out of the first germ-free mouse experiments by Nobuyuki Sudo in 2004.

Germ-free mice changed everything

Sudo found that mice born and raised with no bacteria behaved differently than normally germy mice. It was a stunningly simple, but powerful, observation.

At that time, we were just beginning to realize that gut bacteria were, for the most part, beneficial to us. That was a huge break from the "kill all germs" philosophy. But just what those microbes were doing in our gut was a big mystery. Germ-free mice presented a golden opportunity to investigate.

When Sudo realized that germ-free mice had a different reaction to stress, it was confounding. How in the world could bacteria affect behavior? Sudo then introduced normal gut bacteria to the mice and discovered something else: he could fix their stress response, but only if he inoculated them before they were three weeks old – the equivalent of a human teenager. After that, the window of opportunity slammed shut.

Since then, researchers have shown that this is not just happenstance or a mere association. The relationship is causal. An astounding series of experiments have shown that you can transmit depression by transferring microbes. Most of these studies use fecal transfers, and some have gone from humans to mice, thus demonstrating cross-species causality. In general, feces from depressed animals will make the recipient depressed as well. From a psychiatric point of view, that is truly revolutionary.

What is the mechanism?

Although much more research needs to be done, there are some good theories about how microbes manage to pull off such a feat. One tantalizing piece of evidence is that if you cut the vagus nerve that connects the gut to the brain, many of these effects disappear – implying that at least some of the psychoactive properties of microbes are transmitted by that meandering nerve bundle.

Another shocker is that bacteria know how to make neurotransmitters all on their own. Microbes don’t have brains, of course, but they may use neurotransmitters like dopamine and serotonin to communicate with each other, just like neurons do. They may also be communicating with us as well. There is accumulating evidence that microbes could even be using these chemicals to affect our cravings, another spooky instance of mind control.

Studies show that psychobiotics can improve the mood of even healthy individuals, implying that inflammation may not be the whole story. More research is needed to fill in the gaps in our understanding, but the field is moving quickly.

Can we control our microbes to improve our mood?

The research so far has indicated that healing a leaky gut can go a long way toward improving mood. The best way to do that is to support psychobiotics such as Bifidobacteria longum and Lactobacillus rhamnosis that nourish the gut lining. How do you support them? That turns out to be fairly easy: increase your consumption of fiber and ferments.

Fiber refers to chains of sugar molecules that our body can’t break down, but our microbes can. Properly fed, these beneficial microbes produce substances like butyrate that are excellent gut salves.

Fiber is found in veggies and fruit, two food categories that have dropped precipitously from western diets. Vegetables like artichokes, asparagus, onions, garlic, and beans are full of fiber. So are fruits like berries. An important source of psychobiotics is fermented food like sauerkraut, pickles and yogurt (unsweetened).

Refined sugar and junk food, on the other hand, support pathogenic microbes that may lead to leakiness.

The bottom line

Not all psychological problems start in the gut, and some amount of depression and anxiety is normal and healthy. For those with long-term depression, antidepressants are still popular and effective tools. Still, as Dr. Dinan has found with many of his patients, a psychobiotic alternative has great promise and possibly fewer side effects.

The beauty is that you can try fiber or ferments yourself with a trip to the grocery store. Psychobiotics are complex, involving all bodily systems, and everyone is different due to unique genes, environments, diets and antibiotic history. So pay attention to your psychobiotic adventures and take notes about what works for you.

If you are already being treated by a psychiatrist, make sure to talk to them about diet changes. But even if you are already on a drug regimen, keeping your gut in good shape will never hurt.

If you are a psychiatrist, the lesson of psychobiotics is that it might be wise to check on your patient’s gut as well as their mind. As strange as it seems, microbes affect our moods, and simply eating better could change your life.


Dinan, Timothy G., Catherine Stanton, and John F. Cryan. “Psychobiotics: A Novel Class of Psychotropic.” Biological Psychiatry 74, no. 10 (November 15, 2013): 720–26.

Sudo, Nobuyuki, Yoichi Chida, Yuji Aiba, Junko Sonoda, Naomi Oyama, Xiao-Nian Yu, Chiharu Kubo, and Yasuhiro Koga. “Postnatal Microbial Colonization Programs the Hypothalamic–Pituitary–Adrenal System for Stress Response in Mice.” The Journal of Physiology 558, no. 1 (2004): 263–75.

Abautret-Daly, Aine, Elaine Dempsey, Adolfo Parra-Blanco, Carlos Medina, and Andrew Harkin. “Gut-Brain Actions Underlying Comorbid Anxiety and Depression Associated with Inflammatory Bowel Disease.” Acta Neuropsychiatrica 30 (March 8, 2017): 1–22.

Kelly, John R., Yuliya Borre, Ciaran O’ Brien, Elaine Patterson, Sahar El Aidy, Jennifer Deane, Paul J. Kennedy, et al. “Transferring the Blues: Depression-Associated Gut Microbiota Induces Neurobehavioural Changes in the Rat.” Journal of Psychiatric Research 82 (November 2016): 109–18.

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