Mirtazapine for gastrointestinal and neuropsychological symptoms in older adults with irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common and potentially modifiable contributor to excess disability, morbidity, and poor quality of life. Clinical trials of medications for IBS have largely been in younger adults. Yet, a growing number of adults aged 65 and older are living with IBS. No data exist to guide clinicians in the safe and effective use of medications (e.g., anticholinergics, anti-spasmodics, and tricyclic antidepressants (TCA)) for IBS in the geriatric population. These medications—especially anticholinergics and TCAs—carry a high risk of adverse effects (ADE) in older adults because of age-associated decline in drug metabolism and the high prevalence of multiple chronic conditions. Five or more medications (polypharmacy) are frequently used to treat common psychiatric and medical comorbidities of IBS: anxiety, depression, insomnia, migraine headache, diarrhea, nausea, poor appetite, pruritus/skin atopy, and fibromyalgia. These neurological and psychiatric comorbidities reflect shared pathogenic mechanisms and bidirectional crosstalk of high inflammation, alteration of gut microbiota, and dysregulation of multiple gastrointestinal and central nervous system-active neurotransmitters (e.g., serotonin, neuropeptides). Currently, these IBS-associated conditions are treated with multiple medications—which increase the risk of adverse drug–drug interactions. One way to reduce the number of medications used for IBS-associated conditions is the use of one medication that treats many or all of these conditions—Mirtazapine. In this perspective article, we present evidence from basic science, case series, observational and epidemiological studies, clinical studies, and clinical trials supporting mirtazapine, a noradrenergic and specific serotonergic receptor antagonist—with 5-hydroxytryptamine-2 and 3 antagonism, as a potential pharmacotherapeutic intervention for the myriad symptoms and conditions associated with IBS. Specifically, we found evidence of mirtazapine’s role in treating diarrhea, insomnia, migraine headache, nausea, and poor appetite. We propose a large randomized controlled trial to study mirtazapine as a potential one-stop treatment for multiple IBS symptoms, with the potential to reduce polypharmacy and ADEs, especially in the geriatric population.