(In regard to the negative findings of the massive HPS2-THRIVE study, which have led some to conclude that niacin is not truly protective , these findings are so discordant with much of the rest of the niacin clinical literature that they prompt the suggestion that the laropiprant administered in conjunction with niacin may have exerted a countervailing negative effect on vascular outcomes . Laropiprant inhibits the type 1 PGD2 receptor, and it is unclear as to whether this might itself influence the atherosclerotic process.)