Prozac ineffectiveness over time

I took Prozac for many years.  Six months ago it become ineffective. I now take Wellbutrin instead and it seems to be working well.  However, I need something for OCD.  The Prozac used to address OCD but does not appear to work anymore.  My doctor wants me to continue prozac but I have serious doubts.  Is there a waiting period where in fact the tolerance that I have built up may go away and render the drug useful once again.

[mammo]

Once the drug's effectiveness is gone, it's gone.  Is your doctor a psychiatrist?  They are mosy knowledgeable about which drugs are best for you.  I got quite a few years out of Prozac but then it became useless and I had to switch to a different medication.

[aquamarine_moon]

Not true!!!  It is definitely not at all true that once a drug's effectiveness is gone "its gone".  Everyone's biochemistry is different and for most people (sorry mammo), the drug will work again after a period of being off of it or when it is added as an adjunct to another medication.  I was on Prozac for years, built up a tolerance, switched to Celexa for a couple of years and now am back on the Prozac and it's working fine.  To boost it's effectiveness, my doc added Wellbutrin for a while.  There are many combos that work better for people than just one single anti-depressant.  
I have tried every anti-depressant out there, but the one that worked the first time (Prozac) still works the best for me (if I take breaks in between or use an adjunct med).  Your psychiatrist is likely trying to give you something that s/he knows you did well on in the past because its a more sure bet than giving you a brand new one.  That being said, tell your doc about your doubts and decide together what the best course of action is.  Good luck to you!