Granisetron, has antiemetic properties because of:
Granisetron is 5-HT3 antagonist and is 10 times more potent than ondansetron, and probably more effective during the repeat cycle of chemotherapy. The weak 5-HT4 blockade seen with ondansetron  has not been detected in granisetron. lts plasma t½ is longer (8-12 hrs) and it needs to be given only twice on the day of chemotherapy.
Dopaminergic receptor — blocking actions
Gabamimetic actions
Gaba-inhibitory actions
Serotonin receptor-blocking action