Abstract
Background: When a patent of an active ingredient expires, generic companies can enter the market and offer equivalent drugs to compete against the brand version. Unless the general practitioner (GP) states otherwise in the prescription, i.e. makes a reservation, the patient will be dispensed the generic version in the pharmacy. The patient can still claim the brand version, but has to pay the additional cost himself. There are a few medically justifiable reasons for the GP to prefer the brand version, and about 7% of the prescriptions in Norway have reservations against generic substitution. However, the large variation in reservation between doctors, suggests that many reservations are based on non-medical considerations. Previous research has shown that factors such as price, age of doctor, patient population, pharmacist mark-ups and maturity of generic markets explain some of the variation. Objectives: This thesis investigates the extents to which market conditions and general practitioners characteristics might explain variations in the rates of generic reservation. In addition to the previously studied factors we will introduce some new explanatory variables that, to our knowledge, have not been tested before. Specifically, the effect of competition between GPs in municipalities might provide new insights. Methods: To find links between GP-reservation and the above-mentioned characteristics, data from pharmacy sales and the Norwegian GP-registry were analysed. Both descriptive statistics and alternative models (binary, fixed effects, OLS regression, two-part models) were used to find marginal effects of the variables tested on reservation level. Results: A major contribution of this thesis relates to the gatekeeper function of GPs: our results show that increased competition between GPs results in more generic reservation. Furthermore, older GPs use reservation more often, whilst the effects of sex and speciality are more inconclusive. Increased confidence in generics defined as frequent prescriptions, translates into lower reservation levels. Active ingredients that have recently become subject to generic competition have higher reservation levels. In general, the effects are also stronger in new generic markets as compared to older markets. The results are consistent across the alternative models used.