A very well-known, but very illegal marketing, practice is for drug companies to market a prescription drug for an "off-label" use. While doctors can prescribe a drug for any use they wish, a drug company can only promote a drug for the exact regimen it was approved for.
The former drug company Wyeth, recently purchased by Pfizer, illegally promoted Protonix for certain sub-types of gastro-esophageal reflux for which it had not been approved. Sales people were also trained to promote it for nighttime heartburn even though Wyeth did not have a single medical study confirming that.
Wyeth's successor, Pfizer, has denied all the allegations yet has voluntarily agreed to pay the $55 Million fine to resolve the claims arising from Protonix marketing in 2000 and 2001.