The early signs of ovarian cancer can be confused with irritable bowel syndrome (IBS).

BBC: Ovary cancer signs 'confusion'

McCain can be combative and irritable in his town-hall meetings.

NEWYORKER: On the Bus

Similarly, a former college athlete who becomes angry and irritable in his 40s could be suffering a midlife crisis or delayed reaction to head injuries sustained decades earlier.

WSJ: Confusing Medical Ailments With Mental Illness

My favorite illustration of this is a study written up by Harvard placebo researcher Ted Kaptchuk and colleagues in 2008 in the British Medical Journal. 262 patients with severe irritable bowel syndrome were randomly assigned to either be on a waiting list, to get fake acupuncture, or to get fake acupuncture accompanied by lots of warm talk.

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