Featured Articles

ISMP Updates Its List of Drug Names with Tall Man (Mixed Case) Letters Based on Survey Results

Several design techniques have been explored for the purpose of differentiating look-alike drug names to prevent medication selection errors. Tall man (mixed case) lettering describes a method for differentiating the unique letter characters of similar drug names known to have been confused with one another. Starting with a generic drug name expressed in lowercase letters, tall man lettering highlights the differences between similar drug names by CAPITALIZING dissimilar letters. Occasionally, brand names, which always start with an UPPERCASE letter, may require the use of tall man letters to differentiate them from other brand or generic names. The use of tall man lettering to accentuate a unique portion of a drug name with UPPERCASE letters, along with other means such as color, bolding, or a contrasting background, can draw attention to the dissimilarities between look-alike drug names as well as alert healthcare providers that the drug name can be confused with another drug name.

Since 2008, ISMP has maintained a list of drug names with recommended UPPERCASE and bolded tall man letters. The list includes mostly generic-generic drug name pairs or larger groupings, although a few brand-brand or brand-generic name pairs are also included. Periodically, ISMP updates this list; it was last revised in 2016. Each time the list is updated, we analyze reported events from our error databases, survey practitioners on the topic, and conduct an internal review of drug names that would benefit from the application of UPPERCASE and bolded tall man lettering. The internal assessment includes an exploration of orthographic similarity; patterns of similarities in dosage, formulation, and use; and the potential for patient harm if the drugs are confused.

Standardization of Tall Man Letters

To promote standardization regarding which letters to present in bold/UPPERCASE, ISMP follows a tested methodology whenever possible, called the CD3 rule.1 The rule suggests working from the left of the drug name first by CAPITALIZING all the characters to the right once two or more dissimilar letters are encountered. Then, working from the right of the word back, returning two or more letters common to both words to lowercase letters. When the rule cannot be applied because there are no common letters on the right side of the word, the methodology suggests CAPITALIZING the central part of the word only. When this rule fails to lead to the best tall man lettering option (e.g., makes names appear too similar or hard to read based on pronunciation), an alternative option is considered. ISMP suggests that the tall man lettering provided by the US Food and Drug Administration (FDA) and ISMP be followed to promote consistency.

ISMP Survey

ISMP conducted a survey between October and December 2022 to help update ISMP’s current list of look-alike drug names with tall man (mixed case) letters. We believe healthcare practitioners should be involved in the process of identifying confusing drug names relevant to their respective practice settings, along with reviewing proposed tall man lettering for possible implementation. The CAPITALIZED and bolded letters should make the drug names distinguishable from the user’s perspective.2 

Respondent profile. ISMP extends our sincere appreciation to the 298 respondents who completed our survey on drug names with tall man letters. The respondents were mostly pharmacists (57%), nurses (24%), and pharmacy technicians (12%); however, we also received responses from physicians and other prescribers (2%), and others (e.g., consultant, project manager, respiratory therapist) (5%). The findings from the survey and a discussion of how we updated the FDA and ISMP lists follow.

Scope of using tall man letters. A majority (94%) of respondents reported that their facility uses tall man letters. Almost three-quarters (74%) consistently use tall man letters for organization-defined drug names in all required contexts (e.g., computer screens for pharmacy and prescribers, smart infusion pump drug libraries, labels). Four out of five (80%) respondents use tall man letters in all settings (e.g., pharmacy, surgical suites) and across multihospital and/or multi-clinic settings.

Internal selection of drug names for tall man letters. Fewer than one out of five (18%) respondents use tall man letters for one or more drug names that do NOT comply with the configurations on the FDA and ISMP Lists of Look-Alike Drug Names with Recommended Tall Man (Mixed Case) Letters. However, most of the examples provided by respondents were drug names that were NOT on the FDA or ISMP lists. Examples include doxEPin (confused with doxycycline), nitroGLYcerin and nitroPRUSside, and ALTEplase and TENECTEplase. One respondent notified us that internally selected tall man letters for drug name pairs created confusion because of differences in the tall man letters used in drug information references (which comply with the FDA and ISMP lists). Thus, the organization opted to use the configurations on the FDA and ISMP lists, and to eliminate the use of tall man letters for drug names not included on either list.

Reduction of errors. The vast majority of respondents felt that the use of tall man lettering helped reduce the risk of errors among medications with look-alike names. Specifically, 95% of respondents felt that the use of tall man letters by the pharmaceutical industry on product and carton labels helps to reduce drug selection errors. More compelling is the fact that 87% of survey respondents were able to recall one or more instances when tall man lettering had actually prevented them from prescribing, transcribing, dispensing, or administering the wrong medication. Respondents provided examples of look-alike name pairs involved in these potential events, including hydrALAZINE and hydrOXYzine, levETIRAcetam and levoFLOXacin, and SOLU-Medrol and DEPO-Medrol. Many others reported a personal experience where tall man lettering has helped them avoid errors when selecting drugs during order entry, removing medications from an automated dispensing cabinet (ADC) via override, programming the smart pump using the drug library, and prior to administration when referencing the medication administration record (MAR). Others reported that the use of tall man lettering on preprinted paper order sets helps prevent errors during electronic health record (EHR) downtime when technological safeguards are unavailable.

Several respondents also told us that tall man lettering alerts them to the possibility of a drug mix-up, reminding them to be cautious. They said that tall man letters are an effective alert system that quickly captures their attention and causes them to pause, read the drug name more carefully a second or third time, and make sure the drug is appropriate for the patient. Respondents referred to the tall man letters as a “tool to highlight errors” that helps to “catch your eyes” and “slow down or stop the process” to ensure they have the correct drug and “to prevent confirmation bias” when handling drugs with similar names.

Updated Lists

FDA list. In 2001, FDA initiated the name differentiation project to continually evaluate postmarketing reports of name pair confusion and to determine if tall man lettering should be used to help differentiate similar generic names. Since our last update to the lists in 2016, FDA has added three drug name pairs to its list:

  • CISplatin and CARBOplatin 

  • migALAstat and migLUstat 

  • traZODone and traMADol  

Two of these name pairs were already on the ISMP list: CISplatin and CARBOplatin, and traZODone and traMADol. Also, acetoHEXAMIDE, sulfiSOXAZOLE, and TOLBUTamide have been discontinued and are not marketed in the United States. However, FDA does not want to remove these names from its list because the names might still be listed in electronic drug information sources. Also, unless a drug is removed from the market for reasons of safety or efficacy, the drug could still be marketed at a later date.

Table 1. Drug names tested for possible addition to the ISMP List of Look-Alike Drug Names with Recommended Tall Man Letters

Table 1. Drug names tested for possible addition to the ISMP List of Look-Alike Drug Names with Recommended Tall Man Letters

ISMP list. In the 2022 survey, we asked for feedback on 10 potential new drug name pairs or single drug names that may be confused with another drug name pair already on the list. Of these, 75% or more of the respondents felt that seven of these should be added to the ISMP list of drug names with tall man letters (Table 1). For these seven drug names or pairs, we evaluated the potential for overlap among indications, frequency of administration, storage, drug formulation, and available strengths, along with the potential for harm if a mix-up occurred. We also searched our error-reporting databases to see how often we received reports of mix-ups with a similar-looking drug name. Based on this assessment, the following drug names were added to the ISMP list:

  • cycloPHOSphamide (confused with cycloSPORINE and cycloSERINE, already on FDA list)

  • droPERidol and droNABinol

  • dexAMETHasone and dexmedeTOMIDine

  • pyRIDostigmine and PHYSostigmine

Many respondents shared their thoughts regarding other drug names that were not tested in the survey. We reviewed each suggestion while considering all risk factors and the need to keep the list short enough to avoid diluting the effectiveness of tall man letters. Overuse of tall man letters may reduce effectiveness, as names would no longer appear novel.2 More than 30 name pairs with tall man letters were suggested (many brand names, which we hesitate to include without FDA approval). There were drug name pairs or single drug names that may be confused with other drug names already on the list that were closely associated with a high risk of harm if a mix-up were to occur, therefore, the following were added to the ISMP list:

  • ALfentanil (confused with SUFentanil and fentaNYL, already on the ISMP list)

  • BUPivacaine and ROPivacaine

  • oxyBUTYnin (confused with oxyCODONE, OxyCONTIN, and oxyMORphone, already on the ISMP list)

ISMP has previously recommended NOT using brand names of drugs that have been discontinued (e.g., Versed); thus, three name pairs were removed from the ISMP list:

  • AVINza (discontinued) and INVanz

  • SINEquan (discontinued) and SEROquel

  • TRENtal (discontinued) and TEGretol

In addition, the list was updated to include a notation for a medication that is not currently available in the United States:

  • raNITIdine (not available) confused with riMANTAdine

The FDA and ISMP Lists of Look-Alike Drug Names with Recommended Tall Man (Mixed Case) Letters has been updated on our website.

Ongoing Research

In 2016, ISMP published an up-to-date review of the research, Tall man letters: A review of the evidence; in Special Edition: Tall Man Lettering; ISMP Updates Its List of Drug Names with Tall Man Letters. Using tall man letters, alone or with other text enhancements, has been shown to reduce errors due to drug name similarity. However, the evidence is mixed, with some studies showing the method may not be effective. Interestingly, a 2021 meta-analysis that looked at 11 articles representing 20 individual trials, showed a significant reduction in wrong medication selection errors caused by look-alike drug names when using tall man lettering or other forms of text enhancement. 

ISMP is currently serving as a co-investigator in a 4-year Northwestern University (Chicago) research project, led by Bruce L. Lambert, PhD, to assess the comparative effectiveness of various methods of tall man lettering, text enhancements, and their ability to reduce errors during drug selection. This research project is being funded through a grant from FDA. We look forward to participating in the research project and learning more about the effectiveness of tall man lettering.

Although there are still questions to be answered, tall man lettering is done at little or no cost, has little or no downside, and is not known to be associated with any potential risk for patient harm. Considering past research showing it may be an effective way to prevent mix-ups, and the overwhelming support for tall man lettering shown by survey respondents, ISMP strongly encourages continued use by FDA, pharmaceutical manufacturers, outsourcers and compounders, hospitals, and other practice locations, while we conduct further research to answer questions about the most effective way to differentiate look-alike drug name pairs.


  1. Gerrett D, Gale AG, Darker IT, Filik R, Purdy KJ. Tall man lettering. Final report of the use of tall man lettering to minimize selection errors of medicine names in computer prescribing and dispensing systems. Loughborough University Enterprises Ltd; 2009.
  2. ISMP Canada. Principles for the application of tallman lettering in Canada. October 2015.


Suggested citation:

Institute for Safe Medication Practices (ISMP). ISMP updates its list of drug names with tall man (mixed case) letters based on survey results. ISMP Medication Safety Alert! Acute Care. 2023;28(2):1-4.