How long does prozac stay in your system

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Postby e8andrew » Thu Jun 09, 2005 1:14 am

I was taking Prozac for about a month, I missed about three days the weekend before last and have not taken any since last friday, anyone know how long it is supposed to stay in your system? I know it must be somewhat dependent on the person but just wondering how long on average before one is Prozac free?

Many Thanks

Andrew
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Postby One Small Voice » Thu Jun 09, 2005 1:33 am

Well, being as I'm still here watching out for someone I might as well answer :)


Prozac has an official 'approximate' half life of "between 48 and 72 hours" (why the huge difference beats me!)

Taking a middle line of say 60 hours seems to be the easiest thing for calculation.

Half life is how long it takes HALF of whats in your body to leave.
The next half life takes HALF of whats left in your body to leave. (that would then be a quarter left).
Next half life takes HALF of that quarter to leave your body (leaving an eighth).
Next half life takes HALF of that eighth to leave your body (leaving one sixteenth).
Next half life takes HALF of that sixteenth to leave your body (leaving a ... um... 32 part of the original dose)
Final half life takes half of that remainder leaving a 64th negligible trace of the original dose).


So basically with a half life of 60 hours (which is 2 and a half days), on average you mutliply it by 6 for an estimate of it near enough leaving the body.

SO... 6 times x 2.5 days half life = 15 days?? before its left the body.


Is that right? I'm absolutely shattered and its hard to concentrate.


Going to the other extremes, 6 times a half life of 48 hours (2 days) = 12 days before its left the body.

Or 6 times 70 hours (approximately 3 days) = 18 days before its left the body.


If you're tthinking withdrawal symptoms, its possible for the REDUCTION to cause them - it doesn't have to be left entirely out of the body though thats more usual.


Hope that helps, and if the person I'm looking out for hasn't come back and need a bit more reassurance once I've posted this, then I'm off to bed :)

Nite.
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Postby e8andrew » Thu Jun 09, 2005 3:56 am

For some reason my thread was put up twice :?:

Yeah, it helps a lot, thanks for the physiology/maths lesson as well. Maybe ~15 days would have sufficed but I do very much appreciate the extra details :D .

I assume when it is less and less in my system the effects of it are also reduced relative to this. Maybe only time will tell, I'll see in a few weeks time.

Hope you sleep well

take care

Andrew
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Postby BEwildered » Thu Jun 09, 2005 11:23 am

I read it has the longest half life of any SSRI which I thought was more like 9 days plus. And that when the maths are worked out it takes about 30 days for it to be out of your system completely.

The long half life is why it is recommended if people find feel ill stopping some of the other ones.

So I haven't taken one for about 5 weeks and it only just must be out of me. There seem to be conflicting reports about 1/2 lives.
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Postby One Small Voice » Thu Jun 09, 2005 1:33 pm

BEwildered wrote:I read it has the longest half life of any SSRI which I thought was more like 9 days plus. And that when the maths are worked out it takes about 30 days for it to be out of your system completely.

There seem to be conflicting reports about 1/2 lives.


I've seen conflicting reports too. The half life I put was taken from an expert psychopharmacologist, so I tend to use that one. The thing is, so many things can alter the speed it leaves the body that its only a very rough guide anyway.

LOL now its getting even more confusing. According to that half life given for Prozac, it takes between 12 and 18 days to leave the body, (APPROXIMATELY). Not five weeks. I think you might have multiplied the already multiplied half life?






Hi Andrew,

I explained it that way so you understood how it works and then can calculate it with any drugs half life LOL. Saves having someone reading it and asking... why 6 times?? and then having to go through it again, thats happened a lot in the past so now I just explain the lot all in one go :lol:

Once understood it just leaves remembering that a drug leaves the body in approximately 6 times the half life given.

Half life of any drug is always only approximate, because illness, age, other medications, general metabolism etc all can effect the rate. But I still don't know why prozac is given such a wide figure. With Effexor for instance, half life is simply put as 5 hours, Seroxat is put at 21 hours, sertraline at 26 hours, etc. A mystery.

Slept well thanks :)
Last edited by One Small Voice on Thu Jun 09, 2005 4:03 pm, edited 1 time in total.
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Postby BEwildered » Thu Jun 09, 2005 3:15 pm

Here's that 5 weeks thingy - or one of them:

Fluoxetine has a long half-life (takes 5 weeks to be excreted fully). This is a disadvantage if patients require the drug to be swapped to another, but is useful in patients who occasionally forget their medication. Also helps to prevent any discontinuation syndrome on stopping.

from http://www.ncl.ac.uk/nnp/teaching/management/drugrx/antdep.html


- and another:

drug generic name company type max mg/day Half life, hrs

Prozac fluoxetine Dista SSRI 7 to 9 DAYS
Approx. 7% of people have difficulty metabolising fluoxetine and it then increases rapidly

from ...http://www.clinical-depression.co.uk/anti_depressants/withdrawal/half_life.html


So perhaps it depends on the initial dosage and all those other things.
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Postby One Small Voice » Thu Jun 09, 2005 3:29 pm

BEwildered wrote:Here's that 5 weeks thingy - or one of them:

Fluoxetine has a long half-life (takes 5 weeks to be excreted fully). This is a disadvantage if patients require the drug to be swapped to another, but is useful in patients who occasionally forget their medication. Also helps to prevent any discontinuation syndrome on stopping.

from http://www.ncl.ac.uk/nnp/teaching/management/drugrx/antdep.html


- and another:

drug generic name company type max mg/day Half life, hrs

Prozac fluoxetine Dista SSRI 7 to 9 DAYS
Approx. 7% of people have difficulty metabolising fluoxetine and it then increases rapidly

from ...http://www.clinical-depression.co.uk/anti_depressants/withdrawal/half_life.html


So perhaps it depends on the initial dosage and all those other things.



Yes, there's quite a lot of different statements by different institutions on half life of drugs, I wouldn't worry about it too much. The important thing on that is knowing that Prozac has the longest half life and efexor, then seroxat, is the shortest (out of the SSRIs) - to know enough to be on your guard re withdrawal.


You might have a good point about the initial dosage (or even dosage generally maybe), it might well be one of the factors that determine how fast/slow its metabolized. Have you looked into it? Could be worth doing :)


I'm editing this one - I remembered and I looked for the article I'd seen before re why theres a difference in prozac (fluoxetine) half life ranges, and it might explain as well why different scientific literature gives such different periods for the half life?


"The severity and frequency of the syndrome differs among SSRIs, with variation being attributed to differing pharmacokinetic profiles, more specifically to the individual half-lives and existing metabolites of the drugs. Fluoxetine, which has a half-life of 24 hours and an active metabolite (norfluoxetine) with a half-life of 7 days, causes fewer adverse events upon treatment interruption than paroxetine, which has a half-life of 21 hours and no active metabolite.

Therefore, SSRIs with short elimination half-lives or those without active metabolites are more likely to cause a discontinuation syndrome due to more rapid systemic clearance of the drug from the body. (4) Hence, the clinical advantages and disadvantages of using an SSRI with a long half-life and/or presence of an active metabolite with a long half-life should be considered in individual situations"


Having said that, that one's half life (taking either figure) ALSO differs from other figures given.

Maybe there's a simple answer - that working out a half life is not an exact science (which would bring it into line with the rest of science involving SSRIs lol).


http://www.informedpharmacotherapy.com/ ... d-ssri.htm
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Postby e8andrew » Sun Jun 19, 2005 12:25 pm

Hello everyone and thanks again for your replies,

I have now not taken Prozac for a little over three weeks now and still feel just as good as when I stopped taking them, perhaps even better. Would it be safe to assume that the drug is now not having a great influence on my system??

Many Thanks Again

Andrew
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Postby TheMADDOGG » Tue Aug 10, 2010 1:02 am

e8andrew wrote:Hello everyone and thanks again for your replies,

I have now not taken Prozac for a little over three weeks now and still feel just as good as when I stopped taking them, perhaps even better. Would it be safe to assume that the drug is now not having a great influence on my system??

Many Thanks Again

Andrew



I'm on 20mg dose.I can usually go 5 days without taking paroxetine but by the 5th day,I'm a wreck.I get like a dragging feeling on my eyes(hard to describe) and constant dreams making it hard to get to sleep and stay asleep.Get really anxious and nervous about stuff in general.Endless thoughts go through my head making it hard for me to focus on just one thing.I hate being reliant on the sh**.Asked the doc yesterday to ween me off them.He said take 1 first day then half a one the next day and so on for the first week,then half a one everyday for the next week,then half a one every second day for the last week then see how I go.Woke up on the 6th day feeling I could go it alone but I thought I better follow the doctor's instructions.I've heard you can have really bad withdrawl symptoms goin cold turkey.Damned if I need that.How are you feeling?Did you go cold turkey?
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