The hydrochloride salt form of tropisetron, a selective, competitive serotonin 5-hydroxytryptamine type 3 (5-HT3) receptor antagonist, with antinauseant and antiemetic activities. Tropisetron competitively binds to and blocks the action of serotonin at 5HT3 receptors peripherally on vagus nerve terminals located in the gastrointestinal (GI) tract as well as centrally in the chemoreceptor trigger zone (CTZ) of the area postrema of the central nervous system (CNS). This results in the suppression of chemotherapy- and radiotherapy-induced nausea and vomiting.