Why is it that anti depressants work for fibromyalgia?

Who said they do?: Anti-depressants not proven "to work" for #fibromyalgia. One anti-depressant has purported benefit in "some" fibromyalgia patients. Opiate medications relieve fibromyalgia pain, but are "officially" unapproved in fibromyalgia. Just because drug is "approved" for a condition does not mean way it works is "known". Many "approved" drugs later withdrawn for uncovered harm, e.g., viox, thalidomide.