When Taking Antibiotics, What Happens to Our Mood?

As a therapist who teaches how the mind and body work together, I want to share something you might not hear often: your gut—and the tiny organisms that live in it—can affect your mood more than you might think. And one thing that alters your gut is antibiotics. This doesn’t mean antibiotics are bad or you should refuse them when you need them. But it does mean that being aware of the “after-effects” can help you protect your mental health.

The Link Between Antibiotics & Mood

A large study from the UK found that people who had taken antibiotics had a higher chance of having depression or anxiety later on. The more times they had taken antibiotics, the higher the risk. Specifically, one course of antibiotics raised the odds of depression by about 20–25 %. With repeated courses, the risk went up more. Read more.

Another review of many studies found that antibiotic exposure may increase the risk of depression and anxiety by disturbing the gut’s microbiome—the community of bacteria living in our intestines. Read more.

Let’s break that down into what it means, how it might work, and how you can use that knowledge in your life or therapy practice.

Why Might Antibiotics Affect Mood?

Here are three big reasons we believe the connection exists:

1. The Gut-Brain Axis: Our gut and brain talk to each other through nerves (like the vagus nerve), through immune signals, and through chemicals that bacteria in the gut make. If the gut’s bacteria change, this messaging can shift too. One review said people with depression or anxiety often have different gut microbes than people who don’t. Read more.

2. Antibiotics Disrupt Gut Bacteria: Antibiotics kill or inhibit bacteria—good ones and bad ones. When the community of gut microbes is changed (what we call dysbiosis), it may tilt toward more inflammation or less healthy regulation of mood. Animal studies show antibiotics can lead to “depression-like” or “anxiety-like” behavior in mice by altering gut microbes. Read more.

3. Repeated Exposure = Greater Risk: That UK study showed that one course of antibiotics already raised risk, but multiple courses raised it more. For example: one course was associated with an adjusted odds ratio (AOR) of ~1.23 (so about a 23% increase) for some antibiotics. With 2-5 courses, AOR went up to ~1.40; with more than 5, ~1.56. Read more.

This suggests dose or exposure matters—not just “ever took antibiotics,” but how many, how often.

What Does It Mean for Therapy and Functional Mental Health

From my perspective as a therapist specializing in holistic/functional mental health, this is a really helpful conversation. Here are some practical angles:

• Psychoeducation: When I work with clients, especially those with anxiety or depression, we talk about all the systems involved: nervous system, gut, sleep, nutrition. Knowing that antibiotic use is a possible factor helps us widen the scope of what we watch.

• Tracking history & exposures: I ask about antibiotic history, infections, gut symptoms, digestion, maybe probiotic use. Knowing how many antibiotic courses someone has had can offer clues about their resilience or gut-brain regulation.

• Gut support as part of mental health care: Since we can’t always avoid antibiotics (and we shouldn’t when they are needed), we can strengthen the gut-brain axis: probiotics/prebiotics, fiber-rich foods, stress-reduction, sleep, movement. Even though the research isn’t definitive, it’s low risk and high benefit.

• Integration with therapy of mood: When I see clients whose mood challenges seem poorly explained, I may consider gut-brain health, antibiotic exposure, diet, inflammation—especially if they had lots of antibiotics or gut issues.

• Self-regulation for clinicians and clients: Because the gut-brain connection involves the nervous system, practices like grounding, breathwork, safe relational attunement also help protect the whole system—not just the brain.

Important Notes & Caveats

• These studies show association, not that antibiotics always cause depression or anxiety. It’s not deterministic. Many people take antibiotics and do not develop mood disorders.

• The cited odds ratios (for example ~1.23 for one course) are averages in large populations; individual risk varies.

• Other factors matter: the infection being treated, overall health, genetics, diet, stress, sleep, other medications. Some researchers point out that some of the risk could come from the infection rather than the antibiotic. Read more.

• Much of the microbiome research is still emerging—especially how specific bacterial species relate to mood. So we treat this as promising, not settled.

• The research is mainly observational, meaning we see patterns, not direct cause-and-effect yet.

What I Suggest for Clients & Therapists

1. Ask about antibiotic history. Especially multiple courses.

2. Support gut health proactively.

   • Include fiber-rich foods (vegetables, legumes, whole grains).

   • Include fermented or probiotic foods (yogurt, kefir, kimchi) or probiotic supplements if appropriate (in consultation).

   • Reduce unnecessary antibiotic use (always consult physician).

3. Monitor mood following antibiotic courses. If a client reports a mood dip after antibiotics, we take that note and support them with extra regulation tools.

4. Address lifestyle factors alongside gut/brain health: Sleep, movement, stress regulation, social connection. These buffer the whole system.

5. Use therapeutic tools that address the nervous system and gut-brain regulation: e.g., slow diaphragmatic breathing, orienting to safety in the body, relational attunement, somatic noticing.

6. Collaborate with medical/primary care providers when necessary. If a client is having repeated infections and multiple antibiotic courses, it’s worth coordinating to see if there are gut health, immune, or lifestyle modifications that can reduce the need.

Final Thoughts

The idea that “what happens in the gut affects the mind” might sound a little new or surprising. But the research is accumulating—and as a functional-mental-health therapist I find it helpful because it opens additional doors for healing: we don’t only talk about thoughts and feelings, but about systems—gut, brain, immune, nervous system.

If someone has had multiple antibiotic courses and they are struggling with depression or anxiety, I don’t just say: “let’s talk about feelings”; I might also say: “let’s talk about your gut, your microbiome, how your body regulates, what support you need there.”

It’s not about blaming antibiotics. It’s about empowering clients: our biology is interlinked, and the more we see the connections, the more places we can heal from. If you or a client finds that mood began (or worsened) after a course of antibiotics—or several—then it’s valuable to explore that history, support gut-brain health, and integrate it into the therapy plan.

Here are the key studies to explore:

• Lurie I, Yang YX, Haynes K, Mamtani R, Boursi B. “Antibiotic exposure and the risk for depression, anxiety, or psychosis: a nested case-control study.” J Clin Psychiatry. 2015;76(11):1522-1528. https://pubmed.ncbi.nlm.nih.gov/26580313/

• “Antibiotics and mental health: The good, the bad and the ugly.” Frontiers in Pharmacol. 2023; (PMC article) https://pmc.ncbi.nlm.nih.gov/articles/PMC9796968/

• “Antibiotic use and the development of depression: A systematic review.” PubMed. 2023. https://pubmed.ncbi.nlm.nih.gov/36502554/

• “Gut Microbiota in Anxiety and Depression – PubMed Central.” 2023. https://pmc.ncbi.nlm.nih.gov/articles/PMC12044767/