Drugs that are still undergoing clinical trials do not have a complete void of information about them. Presumably this policy covers drugs that have completed at least some testing in humans (say, phase one of the trials), and therefore at least some information would be available on which doctors and patients could base their decisions.  Further, it is implausible to suggest that doctors are entirely under the sway of advertisers: whilst drug reps under the status quo have some influence in getting a doctor to use one drug rather than another, this is in instances where there is little to choose between those products, and (importantly!) both are licensed, safe and effective. They would clearly not be so reckless as to blindly follow a drugs rep and prescribe an untested product to their patient.