According to a commentary, functional somatic syndromes are groups of symptoms without a clear medical explanation (also known as medically unexplained symptoms) including chronic fatigue syndrome, fibromyalgia, and irritable bowel syndrome concomitantly; pain is commonly reported. They represent a major challenge in terms of diagnosis and treatment. No strong evidence base exists beyond the experience and expertise of practitioners.
It notes that one important reason to be cautious about the result is that there are no comparable studies of imipramine. Another reason is the small size of the trial- in this trial, only 47 patients experienced clinically useful benefit. It suggests the bottom line is that “a substantial minority of people with complex multiple functional syndromes do very well with low dose imipramine at doses much lower than the usual antidepressant dose of 200–400 mg daily.”