Rational prescribing may on occasion be more expensive than irrational prescribing when it involves higher doses, longer courses of treatment or the use of more powerful and expensive drugs. Rational prescribing costs less when unnecessary or ineffective treatment is stopped, or when equally effective drugs that cost less are selected. In practice, irrational prescribing usually costs more.

Identifying irrational prescribing and its consequences is a precursor to training prescribing and dispensing personnel to improve their selection of drugs. The standardization of treatments guides prescribing decisions towards the most rational and least costly form of treatment.

In all cases, the indirect cost of a course of treatment must be taken into account. Poor initial treatment may extend the duration of care, require more expensive care such as surgery, or expose more people to disease. Thus, the number of cases in which the overall cost of rational treatment is more expensive is very limited. Reducing the use of resources for irrational treatment allows these resources to be used for needs that have not been well satisfied. All in all, when care is rationalized, expenditure may be reduced and may sometimes be very high, but the degree to which needs are satisfied will be very much higher.