Doctors go to school for many years to gain the knowledge they have and will prescribe what is needed based on conditions and symptoms, not advertisements.
Prescription drug ads cause people to ask for medications that may not be needed and might even be harmful.
When patients go to their doctor convinced they need a drug that the doctor doesn't think they need some people will go to other doctors until they get what they want and some doctors will prescribe unnecessary drugs just to keep patients.
These ads can have a negative effect on society by advocating drug use as a primary response to conditions that can often be fixed with diet, exercise, stress reduction, and other preventative measures.