I first wrote about the tendency of "promising" treatments to metamorphose into "disappointing" treatments in a BMJ piece about evidence based mistakes. Early results, after all, can't promise anything at all.
The graph depicts a cumulative meta-analysis: each new study is being absorbed into a summation of the evidence so far. With 4 studies, it's shifted from the "this helps" side of the ledger over to the "this harms" side. See more about cumulative analyses in this classic article.
"Promising" is primarily a media and marketing staple, of course. Several wonderful initiatives keep the media to account on this, story by story: Behind the Headlines, the wonderful US Health News Review - and the other related "Media Doctors" in several countries.
This reminds me of the term "emerging evidence" which sometimes seems to mean "The current evidence is not strong but I promise it will become so".
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