Another research article is out regarding lethal injection, in PLoS Medicine. The article says, "the conventional view of lethal injection leading to an invariably peaceful and painless death is questionable." Who decided that was "the conventional view"? Following the article, the editors have a "What Do These Findings Mean?" paragraph. After quoting the above statement, it says this: "The Eighth Amendment of the US Constitution prohibits cruel and unusual punishment. The results of this paper suggest that current protocols used for lethal injection in the US probably violate this requirement."
The conclusion does not remotely follow from the premise. It would be logically valid only with another premise, that anything other than "peaceful and painless" constitutes "cruel and unusual." The editors cite no authority for this remarkable, unstated premise. The methods used from the time of the Eighth Amendment until very recently were certainly not painless. It is one thing to say we do not intentionally inflict severe pain. It is quite another to say we must guarantee a completely painless death. The Constitution does not require that.
Update: Orin Kerr has this post at VC noting the variance between the text of the study and the press coverage of it.