(Please note I do think Effexor worked for me in helping stop very severe depression and stave off mild anxiety for a number of years).
That said, I give you the result and suggestions from my many years of taking and at least a couple times a year suddenly stopping Effexor XR. (btw, people above who are taking *over* 150mg of Effexor, I would have a serious conversation with your doctor about whether the side effects outweigh the symptoms)
I have 100% experienced these symptoms every time I don't take effexor for more than 1 day. I have been taking for years and just recently decided to permenantely stop. Fortunately, I knew what was coming from times I either couldn't afford my script or just forgot to take it, so I did taper off and prepare myself. Make no mistake, you can't just stop taking this sort of medication abbruptly and not expect to have side effects. It directly influences very important chemical levels in your brain, and the system that keeps that in check cannot fully "fix the situation" in 24 hours - or in effexor's case about 2 weeks (different for everyone though). Effexor is a long term medication - especially if you're taking XR. Just like withdrawal, your body's chemical regulation can't be thrown as far off by short bursts of dosing - unlike having it in your system 24 hours a day (which is essentially the goal of the XR).
Here are some things to keep in mind:
1.) If you aren't taking it because you can't afford it, go to your doctor and ask them for samples. It is well known how severe withdrawal symptoms are from effexor, and they will try to help. My doctor gave me a months worth of samples one time because I couldn't afford my script and withdrawal was making me too sick to work or sleep well. I've even had my pharmacist give me a bunch of generics (now that they're out) b/c I couldn't afford my XR script that month.
2.) Plan at least 4 weeks ahead if you want to stop. If you get XRs, you can open them and reduce the amount of little balls inside to taper off without changing your prescription. There are the exact same number in every pill, and they are directly proportional to the dose. So half of the little pellets in a 150mg Effexor XR = 75mg Effexor XR. You can buy some cheap time release medication (like vitamin C) and dump out those pellets to make new smaller effexor pills. That way if your script is 150, and your tapering off, your 150 script would last at least twice as long. Taper down as slowly as you want or can tolerate. Being a little tough and tolerating some symptoms will go a long way towards speeding up time you get to take your last effexor.
2.) I've only found 3 (or 4) things that help with withdrawal symptoms, in order of effectiveness: Xanax, Vicodin, Amino Acids (lots of high quality protein and Omega 3,5,7) Cannabis (but certainly the least effective, not worth pursuing if you don't already use it). Now, I know that sounds like a line up of abused substances (aside from protein and EFAs), but it's my honest experience and if you want to feel better without taking any more effexor I would reccomend you try them. Both of them are potent medications but you only have to take low doses for a couple weeks (in my personal experience) to help quite a bit. I took 2-3mgs per day for alprazolam and 2 5/500 Vicodins a day during the first week of stopping cold turkey and it really did help me a.) sleep and b.) function during the day. I wasn't going to take any more than that because the last thing you want to do is get dependent on something else, although I will say I've taken both xanax and pain killers (oxycontin and pure oxycodone) (after ACL surgery) and withdrawal from those is a joke compared to effexor. You feel sad or get a headache.
I keep saying that half the people I see who are "addicted" to painkillers are either drama queens or just looking for attention - the withdrawal symptoms from effexor put them all to shame.