Antibiotics are among the most commonly prescribed medicines worldwide. In the UK the average person is estimated to take 70 antibiotic courses during their lifetime [1].

Antibiotics contribute to antibiotic resistance but it is also a concern with respect to the detrimental effect that antibiotics can have on the gut microbiome since the majority of antibiotics are not very specific and kill beneficial bacteria as well as the target pathogenic bacteria.

Antibiotic treatments in humans are associated with an increased risk of psychological disorders such as depression and anxiety [2,3]. Furthermore, antibiotic exposure during early life is linked to higher mood and anxiety disorders, as well as behavioural difficulties in childhood [4.5].

In animals, the gut microbiome has been found to alter emotional behaviour and there is a growing number of human studies linking the microbiome to emotion and personality [6, 7].

A team from Leiden, in the Netherlands, recently investigated whether recent antibiotic exposure influences emotional processing of 105 young healthy adult volunteers [1].

Various mechanisms mediate the interaction between the gut microbiome and the brain, including communication via neural signalling, most notably the vagus nerve, and the immune and endocrine systems.

They aimed to assess potential physiological changes in both the immune system (by measuring salivary immunoglobulin A levels) and in heart rate / heart rate variability.

They found that individuals who have taken antibiotics in the past 3 months show a stronger emotional bias towards sadness or depression; they pay more attention to negative/sad facial expressions.

It is known that people who pay more attention to negative emotions have a higher risk of developing mental illnesses such as depression and anxiety.”

On the other side, studies have shown that people who have an infection treated with anti-fungal or antiviral drugs do not have such an increased risk of depression.