Frequent readers of this newsletter know I caution against antibiotic overuse.

Sadly, it’s common for doctors to prescribe antibiotics even when they’re not 100 percent sure the patient has a bacterial infection.

Indeed, research has shown that antibiotic use can result in a host of harmful side effects, including the spread of drug-resistant infections.1 In addition, antibiotics are linked with an increased risk of conditions related to chronic inflammation, including cancer, obesity, and cardiovascular disease.2

And now, researchers have found yet another troubling side effect that will have you thinking twice before filling that antibiotic prescription…

According to new research published in the journal PLOS ONE, long-term use of antibiotics in midlife may lead to cognitive decline in women later in life.3

Researchers understand that antibiotic use could alter the gut microbiome as they kill bacteria of all kinds—even the good ones.

What’s more, these changes to your gut microbiome can last for months or years after exposure to the antibiotics.

The micro-organisms that reside in the GI tract are already known to affect cognition directly.

Still, the evidence linking antibiotic use with cognition was slim until now.

Antibiotics May Influence Cognition 

Researchers from Massachusetts General Hospital and Harvard Medical School examined data from the 2009 Nurses’ Health Study II which includes 15,129 female nurses with an average age of 54.7.4

The team focused on a questionnaire that included antibiotic use over the past four years and the reason for their use. These women also completed a computerized at-home cognitive assessment for dementia an average of seven years after the course of antibiotics.

Top reasons for antibiotic prescriptions included respiratory infection, urinary infection, acne, chronic bronchitis, and dental treatments.

It turns out that compared to non-antibiotic users, women who took antibiotics for at least two months in midlife had lower cognitive scores seven years later.

“We observed that antibiotic use in midlife was significantly associated with subsequent poorer scores for global cognition, learning, and working memory, and psychomotor speed and attention on a cognitive assessment administered a mean of seven years later,” the researchers wrote. “Given the profound effect of antibiotic use on the gut microbiome —the gut-brain axis could be a possible mechanism for linking antibiotics to cognitive function.”

The study authors note that the research provides a better understanding of potential cognitive complications of antibiotic use throughout life. However, the study did have its limitations.

For example, while the study drew from a vast body of data, the information was self-reported by participants. Additionally, participants provided no information on specific antibiotic types.

What’s more, it may be suggested that women who reported long-term antibiotic use were more likely to have chronic conditions with generally poorer health, which might be related to overall cognition.

My Takeaway 

The U.S. Centers for Disease Control and Prevention reminds us that antibiotics are warranted in some circumstances, specifically for bacterial infections. However, they are not effective for treating viruses, such as the common cold.5

If your doctor suggests an antibiotic, ask follow-up questions. If your medical team isn’t sure that the medication is justified, discuss alternatives.

Like many healthcare decisions, there is a risk-benefit calculation that is largely based on a person’s individual medical situation. Carefully weigh your potential benefits against potential risks in your situation.

In the meantime, there’s a long list of things that you can do daily to promote brain health. Regular exercise tops the list, as well as eating a diet rich in nutrients, fresh fruits and vegetables.

Avoid processed foods, smoking and excessive alcohol consumption. Nurture healthy, meaningful relationships, get a handle on stress and make getting regular sleep a priority.

These are all proven modifiable risk factors for dementia that you can address every day through easy and affordable lifestyle changes.

And of course, when it comes to the gut microbiome, experts suggest probiotic supplements may help mitigate the residual damage from antibiotics. I recommend probiotic supplements for everyone whether you’re taking antibiotics or not.


  1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3760005/ 
  2. https://academic.oup.com/eurheartj/article/40/47/3838/5477431 
  3. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0264649 
  4. https://nurseshealthstudy.org/about-nhs 
  5. https://www.cdc.gov/antibiotic-use/q-a.html 

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