Complex sentence: As of 2015 tramadol was not approved in the United States for fibromyalgia and there was some evidence based on three trials weak in statistical power and study design that tramadol might be useful as a second line treatment.
Split into simpler sentences: As of 2015 tramadol was not approved in the United States for fibromyalgia. There are three small trials with weak study design that tramadol might be useful as a second line treatment.