With, or without continuing monitored dosage to account for the body's corrections towards what it perceives as equilibrium? If without a continued dosage, is this before or after a "withdrawl" phase?
The efficacy of SSRIs isn't dose dependent. And the the monoamine hypothesis is a long disproven myth.
This is rather surprising, given that most pharmaceuticals are, and contradicted by the experience of people I've known who've been prescribed them and advised to taper withdrawal - which is then experienced as reducing effectiveness.
Someone with a major mental illness might just do worse after a couple of years, despite medication. Some folks with bi-polar disorder truly can't work, despite the medications, for example. They'd definitely be doing "worse" after starting their medications, some of which might easily include SSRIs, but it isn't really because they started medications.
None of this means we shouldn't use them, just use them responsibly with a bit more medical oversight. After all, for some people these really do help.
The argument (based on some large scale trials and other data) is that after 2+ years, those on SSRIs are worse off than they would have been without them.
The issue is that by taking SSRIs, you may be getting a few weeks of negligible benefits in exchange for a lifetime of being disabled, when otherwise you'd have been better after a few months using other interventions.