Clinical perspective, offered as context rather than as advice. The honest answer is that the effect is real, the magnitude is contested, and the individual variation is larger than either. Those three things can all be true at once, and most arguments here are two people holding different parts of that.

If somebody has the primary source to hand I would rather cite it than paraphrase it.

FDA_TrackerJim said:

If you are going to change something, change one thing and give it long enough to express itself.

Right, and the exception is worth naming rather than left implied, because the exception is where people get into trouble.

FDA_TrackerJim said:

If you are going to change something, change one thing and give it long enough to express itself.

This answered a question I did not know how to ask.

Adding the clinical framing, because it changes how the question reads. Worth answering the question that was asked rather than the one behind it. The narrow version usually has an answer; the broad version usually does not, and answering the broad one is how a thread stops being useful.

Moderator note: good thread. Keeping it here rather than moving it, because the question is general enough to be useful. Report rather than reply if it drifts again.