Posted by SLS on September 30, 2000, at 19:18:38
In reply to Re: Half-life of Effexor, posted by stjames on September 30, 2000, at 14:10:48
> > I was recently started on 37.5 mg Effexor, which I take in the morning. I am wondering if the drug has a really short half-life, or if I am imagining things, because I feel a slight crash from it when it wears off in the late afternoon. I get more anxious and restless and sort of agitated. Could this be from the medication wearing off?
>
>
> James here.....
>
> Unlike most AD's Effexor has a very short half life, measured in hours, instead of the usual weeks. If you are not taking Effexor XR you should. I can get by with once a day dosing on XR
> otherwise you would need to dose 2X a day. Effexor XR also has fewer side effects like nauesa.
>
> James
Hi guys.The half-life of Effexor (venlafaxine) is about 5 hours. That is very short for an antidepressant. Most are about a day or so. The only antidepressant that I am aware of for which the half-life is greater than 48 hours is Prozac (fluoxetine). Fluoxetine has a half-life of about 5 days. However, its active metabolite, norfluoxetine, has a half-life of anywhere between 7-15 days, the average being 9 days. One of the reasons why one must wait for between 4-8 weeks to fully evaluate its value is because it takes 4-5 weeks just to establish a steady-state blood level at any one dosage. Ouch.
Paxil (paroxetine) is another antidepressant that has a relatively short half-life. The average is about 11 hours. However, there are huge differences between individuals as to how long it can be. In some people, the half-life can be as short as 3 hours or as long as two days. Perhaps not surprisingly, the withdrawal syndrome seen upon the discontinuation of serotonergic drugs is worst for Effexor and Paxil.
- Scott
poster:SLS
thread:45523
URL: http://www.dr-bob.org/babble/20000926/msgs/45549.html