- Has a clinically significant unstable illness, for example hepatic impairment or renal insufficiency, or a cardiovascular, pulmonary, gastrointestinal, endocrine, neurological, rheumatologic, immunologic, hematological, infectious, dermatological disorder or metabolic disturbance. NOTE: For the purposes of this study, the following conditions were considered unstable due to the potential impact on assessment of MDD response: pain disorder, chronic fatigue syndrome, fibromyalgia, and obstructive sleep apnea.