A 5-HT3 receptor antagonist is primarily used to reduce nausea or vomiting during chemotherapy but the drug is finding immune, neurotoxic, pain, skin and other applications. Tropisetron started as an anti-nausea but is finding many other applications Pain - Tropisetron reduces receptor activity associated with serotonin’s ability to enhance pain, fear and anxiety. 5-HT3 receptor antagonists both block serotonin’s pain facilitating properties andincrease GABA availability. Tropisetron Might Work in Fibromyalgia and/or Chronic Fatigue Syndrome Because of its neuroprotective, immune modulating and its ability to reduce pain and sensory gating issues and enhance cognition. Tropisetron helped to normalize cardiac autonomic nervous system functioning and reduced ‘pain perception’ in a 2007 study. Forty-five percent of patients in a large 2004 trial reported having ‘good’ to ‘very good’ results in a large 2004 retrospective fibromyalgia study. Fifty percent of FM patients in a small trial reported Tropisetron had a good or very good influence on their pain with serum substance P levels dropping in the responders. Reduced activation of brain regions associated with pain production occurred in another small Tropisetron study. Forty percent of participants reported a greater than 35% reduction of pain in a large 2001 Tropisetron fibromyalgia trial. The number of tender points and sleep and dizziness were also significantly improved.