As most everyone else has suggested: I wouldn't take that big of a decrease right off the bat. I'd start off gradually... 15%-25% less each month. I myself am currently tapering off of my prescribed Vicoprofen & Dilaudid medications for my chronic shoulder pain. This is how my doctor and I have been doing it and it's worked extremely well, with little withdrawal symptoms (most days that is):
Original Scripts: (120) 7.5mg Vicoprofen | (120) 8mg Dilaudid
1st Month Taper: (120) 7.5mg Vicoprofen | (120) 2mg Dilaudid
2nd Month Taper: (120) 7.5mg Vicoprofen | (120) 2mg Dilaudid - didn't change this month's scripts, as the drop from 8mg to 2mg Dilaudid was pretty rough
3rd Month Taper: (90) 7.5mg Vicoprofen | (90) 2mg Dilaudid
4th Month Taper: (60) 7.5mg Vicoprofen | (60) 2mmg Dilaudid
I'm currently on my 4th month of tapering. Next month I'll probably get lowered to 30 of each script. It's a slow process but it's completely worth it because like I said I'm having minimal withdrawals. Admittedly, I also have Xanax and Clonodine scripts for "as needed" symptoms... but I don't have to take them every day. Usually just on the occasional rough day, or at night if I'm having trouble sleeping. But my point is this: start off slower than you're planning... especially if your meds are a legit monthly script from a doctor. Talk with him and get on the same game plan if you think it'll help.