There are two commonly used prevalence measures: the point prevalence and the period prevalence.

The period prevalence is the most commonly used in drug utilization studies and describes the proportion of a population that are users of a drug at some point during a specific period, often a year. The numerator thus includes both new users and continuous (prevalent) drug users, while the total population is used as denominator. As such, the prevalence is a mixture of both existing drug users and new drug users. An example which uses a period prevalence is: “the proportion of the population filling at least one prescription for a proton pump inhibitor in 2020 was 10%.”

The point prevalence similarly describes the proportion of a population using the drug, however, at a specific point in time (e.g., “7% of the population used a proton pump inhibitor on January 1st, 2020”). Although some individual‐level databases on drug use contains a “days' supply” variable (e.g., US data sources), many individual‐level drug dispensing databases do not contain this information. Hence, when using databases without this information, estimates of point prevalence is often based on strong assumptions about the prescribed daily dose and the prescription duration. Importantly, when reporting and interpreting period prevalences, it is important to keep in mind that the period prevalence estimates the number of drug users over a period of time. Thus, depending on the length of this period and the duration of drug treatment, estimates of a period prevalence will be higher than the number of drug users on a specific day. Consider the example where the number of users of antibiotics is counted during a full year versus at a specific day in that same year. Since antibiotics are used only for short periods, the number of drug users at a specific day will be markedly lower than the number of users counted during the full year. For drugs with high discontinuation rates, for example, drugs against attention deficit/hyperactivity disorder, 3 use of period prevalence might, for the same reason, lead to misunderstandings or misinterpretations about the total number of drug users. In general, the time period over which the period prevalence is measured should be carefully considered and depend on the type of drug being studied. For drugs used short term such as, for example, antibiotics, a count of the number of dispensed prescriptions in a time period may be a better measure of drug use than the period prevalence