OBJECTIVES: : Many factors including patient, physician, medicine promotion and price affect prescribing of a medicine. The present study is aimed at showing the parameters that affect prescription writing and determine the effect of each of them on prescription process in Iran. METHODS: In order to investigate the effect of price, advertisement, gender, and age on the sales and prescribing process of three medicines, namely fluvoxamine, clopidrogrel and latanoprosta, pooling data method in econometrics (Panel data) was used. RESULTS: :We found that advertisement and medicine insurance coverage had significant positive effects on prescription of all three medicines whilst negative relationship were seen between increasing price and the frequency of prescription of a medicine. Besides, we found out that advertisement has a direct effect on raising the demand and prescription of the medicines CONCLUSIONS: : Pharmaceutical companies need special attention to the index of physicians like age and sex in planning for sales and marketing of its products