Especially because you have been on it so long, I would urge you to discuss a weaning-off schedule with your doctor, and research thoroughly as to what you could expect.
I'm almost at the end of weaning off of Effexor after 12 years, and it's going well (SO much better than I expected, after all the horror stories I had heard/ read.). But I was prepared, and also have the ready assistance of my med pros who said to call if anything out of the ordinary happens.
It's definitely worth taking the time do do it this way. I undertook my schedule with a lot of confidence.
Keep in mind, too (anyone reading this): Some meds cannot be reduced simply by halving or quartering them---if they are contained within extended release capsules, this means that once the capsule is broken open, the medication will take a different path through your system. I know from speaking with another friend through her changeover that this was a huge mistake for her to do! She suffered unnecessarily for a few weeks before going about it the recommended way.
(((Huggs!!))) I wish you success with your change. Sending best wishes!