Strangely enough, there was a study out not too long ago that had the opposite results. Granted, the subjects were older men, but protein synthesis obviously wasn't an issue.
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"Taking daily recommended dosages of ibuprofen and acetaminophen caused a substantially greater increase over placebo in the amount of quadriceps muscle mass and muscle strength gained during three months of regular weight lifting, in a study by physiologists at the Human Performance Laboratory, Ball State University."
Either way, the negative effects on the liver in long-term use would cancel out any positive anabolic response.