The withdrawal side effects of the commonly used antidepressants is closely related to their half life. That’s one reason effexor withdrawal is such a common and difficult problem. The serum half life of effexor is 5 hours (plus of minus about 2 hours) in most individuals. The apparent half life of Effexor XR, the sustained release product most commonly used in the U.S. is more like 15 hours, but this really reflects the absorption dynamics of the extended release product. Once in the blood stream the real half life is quite short.
The half-life of a drug is the time it takes the body to rid itself of half of the drug in the bloodstream. For example if a drug had a peak serum concentration of 10 mcg./dl and it took 6 hours for the level to drop to 5 mcg./ dl. then the half life would be 6 hours.
Here is the approximate half life of several of the commonly used antidepressant drugs. You will notice that the drugs with the shortest half lives tend to be those with more common significant withdrawal syndromes.
|Effexor||5 hours||XR gives longer functional half life|
|Pristiq||Likely <5 hours||Only avalable in ext. release form|
|Paxil (paroxetine)||21 hours||Withdrawal quite problematic|
|Zoloft (sertraline)||24 hours|
|Celexa (citalopram)||35 hours||Withdrawal much less common|
|Prozac (fluoxetine)||7-9 days||Withdrawal unusual|
|Bupropion||21 hours||Tends not to have withdrawal symptoms|