"One of the hidden secrets of the medical literature is that the named authors on a paper's byline, particularly in the case of clinical trials, are not necessarily the individuals who wrote the paper. It is not uncommon for pharmaceutical companies, or medical product manufacturers, to write their own papers and then find university professors to agree to be the named authors of the paper. The company employees are then invisible to the readers. Presumably, the suggestion that a certain medication or medical product is safe and efficacious will carry more weight if it comes from an unbiased source, often called a Key Opinion Leader, rather than a company representative. With ghostwritten papers it is hard to know where to draw the line between science and marketing. Because of its secretive nature, the true extent of this practice is unknown."
Full article: A Three-part Series on Medical Journal Ghostwriting
Natural Society: FDA: Drug Companies Faked Thousands of Drug Documents
Natural Society: Scientists and Doctors Falsifying Research Data for Publication
Los Angeles Times: Stealth Merger: Drug Companies and Government Medical Research