1. How many drug names are there?

There is no simple answer to this question because there is no single, authoritative, official list of drug names. There are instead, many lists of drug names, with varying degrees of overlap. We reported previously1 that there were 21,687 unique one-word names in the pharmaceutical category (i.e., international category 5) of the U.S. Patent and Trademark Office’s database of registered trademarks2 and 5331 unique generic names in the USP Dictionary.3 However, many trademarks in international category 54 of the USPTO database refer to products other than drugs. Hence, 21,687 is a significant overstatement of the number of proprietary drug names in use in the U.S. We recently examined five different sources of prescribing frequency data: (a) the National Ambulatory Medical Care Survey (NAMCS)5, (b) the National Hospital Ambulatory Medical Care Survey (HAMCS)6, (c) the IMS National Prescription Audit Plus (NPAP)7, (d) the Solucient· outpatient frequency database, and (e) the Solucient hospital drug utilization database.8 These data suggest that there are no more than 11,000 drug names currently in use in the U.S., and no more than 4400 one-word names. In a related study, we combined the names from the FDA’s Orange Book9 and from the Multum Lexicon.10 After removing generic names and duplicates, there were 5232 unique brand names remaining, of which 3681 were available only by prescription and 1551 were available over-the-counter. Due to inconsistencies in drug nomenclature and problems in automatic processing of the names, these should be regarded as estimates rather than definitive counts.


2. How are names chosen?

There is no uniform method for selecting brand or generic names. Typically, brand names are chosen by the manufacturer of the drug, in consultation with specialized brand-naming companies or consultants such as Brand Institute, InterbrandWood, or Lexicon Branding. A great many factors go into the selection of a brand name, including its length (it should be short), its spelling, its sound, and its direct and indirect meanings. A company may begin with hundreds of names before legal, marketing and safety considerations narrow the choices to 10 or fewer. The final decision about a name reflects a complex decision making process that attempts to balance several competing concerns (e.g., confusability, memorability, pronounceability, meaning, etc.).


3. How are names approved?

There are multiple routes of approval for drug names. The approval process for proprietary (i.e., brand, trademark) names is different than the process for non-proprietary names (i.e., generics). To be registered as a trademark, a name must be examined and approved by the trademark registration office of the country in question. In the United States, this is the U.S. Patent and Trademark Office. Generic names may be submitted by the manufacturer or may be coined by the United States Adopted Names Council (USAN). The USAN Council makes final decisions about the acceptability of generic names.


4. How many names confusions have happened?

No one knows for sure because there is no effective surveillance system in place to detect these errors. The U. S. Pharmacopeia has published a report based on their error reporting system and has set up a site where users can search their database of name confusions. A study published by Betsy Flynn in 2003 reported that wrong drug errors occurred in 0.13% of all prescriptions dispensed in the outpatient pharmacies they observed.


5. What are the consequences of drug name confusions?

The consequences of a name confusion depend totally on the context. Which drug was prescribed and which drug was dispensed? How long was the patient exposed to the wrong drug? How long did the patient do without the right drug? How toxic was the wrong drug? Was the wrong drug contraindicated with the patient’s disease or other drug therapy? How vital was the right drug? How vulnerable was the patient (e.g., any liver failure, kidney failure)? Was the patient hospitalized or at home? Depending on all of these factors, the consequences can range from harmless to fatal.


6. What are some examples of drug name confusions?

The United States Pharmacopeia, in cooperation with the Institute for Safe Medication Practices, periodically publishes lists of confusing pairs of drug names. A PubMed search using “drug name confusion will yield a large number of relevant publications. If the PubMed search is limited to letters only, many case reports will be identified. Our own database of product confusions identified from the English language scientific literature can be downloaded here. (insert link)


7. What can be done to prevent drug name confusions?

The Institute for Safe Medication Practices has advocated a variety of steps that should be taken to minimize drug name confusions. In addition to these, drug companies and regulators should be more systematic and objective in their pre-marketing evaluation of new names. The FDA now requires that companies submit safety studies of new drug names when they are submitted for approval. Several companies now offer some sort of safety screening of new drug names. This screening may involve computerized searches of drug name databases as well as experimental studies of memory errors as well as visual and auditory perception errors.


8. How do you measure similarity?

Similarity is measured along several different dimensions: spelling, pronunciation, and non-name drug product attributes such as strength, dosage form, and route of administration. For spelling similarity, we use a variety of measures including n-gram measures, edit distance, and various hybrids of these techniques. A paper by Justin Zobel and Philip Dart does a nice job summarizing these measures in the context of telephone directory searches. Our presentation for Health Canada also summarized the different methods for measuring similarity in the context of drug names.


9. How is similarity related to confusions?

Generally speaking, our research has shown that the probability of confusion is correlated with similarity. In other words, the probability of confusion increases as the similarity between names increases. We have observed this in short term (recognition memory) and in visual perception. In immediate free recall of drug names, similarity appears to have a beneficial effect on accuracy, probably because participants use rhyming heuristics as cues to recall. Outside the domain of drug names there is an enormous literature in psycholinguistics that documents the relationship between similarity and error in the context of ordinary English words. Google searches using queries such as “false recognition word,” “false recall word,” or “neighborhood effects word identification” should be productive.


10. How is frequency related to confusions?

Generally speaking, frequent words (those that are more often written, spoken, read, or heard) are easier to perceive and remember. Perhaps more importantly, the relative frequency of two similar words will strongly influence the direction of an error. That is if Drug A and Drug B are similar, and if Drug A is much more commonly prescribed than Drug B, then errors will tend to go in the direction of Drug A, the more frequently prescribed drug. In other words, when Drug B is prescribed, Drug A may be mistakenly dispensed due to errors in memory and perception. But Drug B will rarely be dispensed instead of Drug A. These effects can get quite complicated when one tries to simultaneously take into account the effects of similarity and frequency. Again, the psycholinguistic literature on “neighborhood effects” would be instructive.


11. What is FDA doing?

The FDA has recently released a concept paper on their approach to screening drug names prior to aproval.



*  Some data for use in this study were supplied by Solucient, LLC, Evanston, Illinois. Any analysis, interpretation, or conclusion based on these data is solely that of the authors, and Solucient disclaims responsibility for any such analysis, interpretation or conclusion.


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  1. U. S. Food and Drug Administration. Electronic Orange Book data files. Web page] Accessed January 28, 2003.
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