Definitely a matter for medical evaluation.
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I did not find specific info re XR's and regular's half-lives, but did find this: "Effexor XR provides a slower rate of absorption, but the same extent of absorption compared with the immediate-release tablet." The XR version evens out the amount in your system over the course of the day; that may mean the half-life of some of the drug is extended, but that's probably just a few hours.
You will know if you are tapering too fast–withdrawal symptoms are the big tip off. Only you can decide if they're tolerable, or not. If not, the recommendation is to go back to the level where you felt good, stabilize at that dose for weeks (or even months) before tapering again (you may want to taper less than 10% from this point on).
If you dropped from 150 to 37.5 over some weeks, you are tapering too fast–feeling like cr*p is the big tip off. Ping-ponging on/off from one day to the next is just putting you into withdrawal over and over. The recommendation is to go back to the level where you felt good (that may be 75mg, or even 112.5mg), stabilize there for weeks, or even months before tapering (only 5-10%, or even less) again. Going slooowww is your friend! There's no point rushing the process if you ultimately can't get off Effexor because the withdrawals are too awful.
Is your doctor on board? He can help you taper off Effexor by prescribing a different formulation–changing from extended-release to regular release, or from capsules to tablets (I was on 25mg tablets that could be cut), or specifying a certain brand (@farm_mom found Teva had the most consistent size and number of beads within a capsule–helpful to those counting and throwing out beads to taper). Or your doctor can write a prescription for a compounding pharmacy to make tapered doses for you (the extra cost may well be worth it because you can glide down in incremental amounts, rather than make rather large jagged drops).
Sun, Nov 3 11:19pm · Tips on minimising withdrawal symptoms from Effexor (aka Venlafaxine) in Depression & Anxiety
Very few, if any doctors have any idea how to get a patient off Effexor and usually recommend far too quick tapers. If you read all the posts on this forum, the most successful way to get off Effexor is to go very slowly–which means tapering by very small reductions (5-10%, or even less) and staying at each new level for quite a while (weeks, or months) before tapering again. The longer you have taken Effexor and the higher your dose, the longer your taper should take. Ping-ponging on and off Effexor every few days just puts you into withdrawal over and over again. Reducing SLOOWWWLY significantly minimizes the unpleasant (and sometimes debilitating) withdrawal effects. Tapering in just weeks can be very uncomfortable and often unsuccessful. Read why and how better to get off Effexor here–
OTC medications and supplements can help with some of the withdrawal symptoms (click on my name and read my past posts for some). Here's a good article re how to mitigate withdrawal effects with supplements (fish oil may be more helpful than krill oil; I also take GABA; do not take L-tryptophan while still on Effexor)–https://www.4mind4life.com/effexor-withdrawal-symptoms.
Ask your doctor about a "Prozac bridge"–"The only way doctors know to soften the blow when withdrawing from short half-life drugs [Effexor is such] is to add fluoxetine (Prozac). The half-life of Effexor is 5 hours and 99% of it is out of your body in one day. Prozac's half-life is 4 to 6 days and it takes 25 days for 99% of it to be out of your body. Essentially, the Prozac cushions the effect of no Effexor and lets you "ride out" the withdrawal process. You can add 20mg of Prozac to any other antidepressant and then get off the [original drug]. Once the [original drug] is gone, you can taper off the Prozac. This works because fluoxetine (Prozac) has a long half-life making it much easier to get off of than drugs like [Effexor].–https://natashatracy.com/treatment-issues/withdrawal/antidepressants-effexorpristiq-venlafaxinedesvenlafaxine/. See also https://www.depressionforums.org/forums/topic/107532-coming-off-of-effexor-with-prozac-bridge/.
Sun, Oct 27 5:10pm · Tips on minimising withdrawal symptoms from Effexor (aka Venlafaxine) in Depression & Anxiety
Not quite 18 years at 25mg daily regular release for hot flashes.
Sat, Oct 26 3:25pm · Tips on minimising withdrawal symptoms from Effexor (aka Venlafaxine) in Depression & Anxiety
Sandi–Getting off Effexor is HARD! My last dose after tapering over two+ months from a 25mg tablet was 4/14/18–I still am struggling with the withdrawal effects!
You tried really hard. You figured out this attempt is not working. You've got a plan to deal with the now. You might try again later. "Better to have tried and failed, than never to have tried at all." Others on here have gone back to the drawing board; we're all trying to figure out how to get off this stuff. Hope you are feeling better soon.
Sun, Oct 6 10:59pm · Tips on minimising withdrawal symptoms from Effexor (aka Venlafaxine) in Depression & Anxiety
I was taking Effexor/venlafaxine for hot flashes, not other issues. I found great relief from the withdrawal symptoms (fear, agitation, anxiety and insomnia) by supplementing with L-tryptophan, GABA, ashwaganda, l-methylfolate and fish oil five times per day and about three days per month 1/2 of 5mg valium. Over fifteen months, I am now down to two doses of supplements per day. You can click on my name and read past posts to see my list of supplements and dosages.
Sat, Aug 10 2:49pm · Tips on minimising withdrawal symptoms from Effexor (aka Venlafaxine) in Depression & Anxiety
Failure doesn't come into it; how you respond (or don't) to a medication isn't a character flaw. Antidepressants are VERY powerful and are DESIGNED to mess with your head–of course, it's going to take some time and real effort to get off them and YES, sometimes, you find out you do need to be on them.
@sandij has a good point about ping-ponging on/off other ADs over a short period of time although I certainly understand how awful the anxiety and agitation/restlessness can be–I wanted mine to stop NOW. I did not use Prozac, but was prescribed Valium to take as needed and started taking a LOT of supplements. You can click on my name and go back and read my posts.
I was on 25mg Effexor for 18 years for hot flashes. It's only NOW–16 months after my last tapered dose–that I feel NORMAL. AND that's with me still taking supplements (L-tryptophan, GABA, ashwaganda, fish oil and L-methylfolate). I haven't been posting here for a couple of weeks because feeling normal has been so STARTLING that I keep waiting for "the other shoe to drop." My husband asked if I was going to discontinue one set of supplements because I'm doing so well–honestly, I'm afraid to mess with success right now! (Although I probably will after a few more weeks of normalcy as taking all this stuff is not cheap.)