Ruling on gifts given by pharmaceutical company reps to doctors

My question is about what is done by advertising reps of pharmaceutical companies. Nowadays some or most of these companies operate by means of gifts or bribes. They give gifts to doctors so that they will prescribe the drugs that are produced by these companies, and the reps fear for their positions in the companies if they do not do that. Many doctors will not prescribe drugs for patients because they have not been given gifts, and will only prescribe the drugs sold by those who have given them gifts. So the reps are forced to compete with other companies in the matter of gift giving. What is the ruling on this? 
Is it regarded as a case of necessity because he fears losing his job, or not? Especially since he may have financial obligations which he must fulfil.