From: assesment and treatment of patients with M.E/C.F.S:clinical guidelines for psychiatrists. By Eleanor Stein MD FRCP(C) "Drug Dosage and Drug Sensitivity It is widely accepted that some patients with ME/CFS are more sensitive to the adverse effects of medication than most healthy people. They share this trait with chronic pain and fibromyalgia patients......SSRIs which are generally well tolerated for the treatment of depression and anxiety are not tolerated by a subgroup of ME/CFS patients. The mechanism of these reactions is unknown." I have had this problem, having had a catastrophic reaction to Citalopram 3 years ago, which took me nearly a year to recover from. Does anyone here know why this happens or what is going on physiologically to cause this. Also does anyone have any more info on the "subtype" she refers to? Any other experiences of this? Justyx.