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.