It depends on what chemo you've had, to a great extent, and also what other meds you've been given.
If you're on Tax, then the dex is essential not only to ward off sickness but to ward off allergic reactions which could be very unpleasant. That's why you get so much, and have to start it the day before.
If you're on FEC then it's less of an issue, and also there are other anti-sickness meds that may work better in conjunction with dex.
This would be a good question to throw at the Helpline, so give them a ring and see what they say.
I'm on Emend (wonderful stuff!) and have cut right down on the amount of dex I take afterwards, because I have been able to manage ok without the full 3 times a day for 3 days thing and take much less.
