A lot of depression studies seem to consider 8 weeks the standard time to effect for antidepressants. Is anyone using less time? 6 weeks? Would you consider that enough time to be 'stable' or have appreciated any treatment response?
How good is the evidence that antidepressants (or antipsychotics for that matter) take weeks to have any effect?
I'm not an expert in this area, but every psychiatrist I've known and every textbook I've read seem to agree that the initial response typically is felt in 2-3 weeks, with the full effect typically present in about 6 weeks - assuming there is no need to tinker with dosing or anything along the way. I'd say that if that's right, setting 8 weeks as the standard makes a lot of sense. After all, some people will respond faster or slower than the average - it's like measuring 5-year college graduation rates when the expected span is 4 years; you have a fair number still working on it.
My sense, though, is that you're asking a viable question that could readily be answered using data from a large clinical trial. After all, the researchers on these studies typically assess symptoms every week or two. So you could examine the number of patients showing a given response, or the mean response level across all patients, for each interval. If the 6-week results are indistinguishable from those at 8 weeks, then you could make a good case for changing the standard - which would save a lot of money in future trials. (It would be surprising if this was true and nobody had looked before. But stranger things have happened.)
I stand ready to be contradicted by an expert psychopharmacologist.
Thanks Stephen. I'm sure you're right.
If anyone has already done this work - ie assessing for whether 6-week results are only marginally different from 8-week results - I'd be grateful to know about it.
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