In the past, there was the odd pharmaceutical representative who got the job without being a graduate of a university or college but those days are over. Due to the large numbers of qualified candidates out there for pharm jobs, a degree would be a must. Although science or business degrees are preferable for most pharmaceutical companies, one can still get in with other backgrounds.
I have met many pharmaceutical representatives who have backgrounds in engineering and arts without much biology knowledge. But one does have to show that he or she has the capacity to be trained as all new pharm reps will be put on intensive training programs by pharma companies to ensure that they do have the required scientific knowledge in order to effectively sell the drugs they will represent.
Candidates without any science background will need to carefully craft their cover letters and resumes so that their particular backgrounds will not become liabilities when applying for pharm rep jobs. For more details on how to do this, see Pharmaceutical Representative Positions.