Let's take a minute to talk about your medication.  

This is Ondansetron ODT, and it is an orally-disintegrating tablet.  You should take your dose as directed by your doctor.  It is important to keep the tablet in the sealed package until needed.  When it is time for your dose, you should peel the backing off the package, instead of pushing the tablet through it, and make sure your hands are dry.  Also, you should allow the tablet to dissolve, then swallow your saliva.  Drinking water with your dose may cause a headache in some patients, so it is not recommended.  

Ondansetron helps prevent and treat nausea and vomiting.  You'll probably start feeling better in about 30 minutes, but it can take a little longer for full effects to occur.  

Ondansetron is usually well tolerated, but some side effects may occur, like headaches, fatigue, or constipation. These are normal and should go away.   But, if these or other side effects become reasons you want to stop taking this medicine, please talk to your doctor or pharmacist.  

For best results, take Ondansetron as directed, and follow your doctor's advice for dietary changes that may also help you feel better.