Special Edition: Tall Man Lettering
ISMP updates its list of drug names with tall man letters
June 2, 2016

One in every 1,000 medication orders in a hospital, and one in every 1,000 prescriptions in a pharmacy, have been associated with selecting the wrong drug while prescribing, transcribing, dispensing, or administering medications.1-4 One of the key causes of these errors is drug name similarity.5 Factors that increase visual similarity among drug names include similar length of the names and the number of groups of similar characters or the same characters within the names. Other risk factors that increase the risk of confusion between similar drug names include similarities in strength, dosing, route of administration, dosage forms, indication, the environment in which the drugs are used, the frequency of use, and product labeling.6

In response, a number of design techniques have been explored for the purpose of differentiating look-alike drug names. Tall man lettering is one such technique. Tall man lettering, a term coined by the Institute for Safe Medication Practices (ISMP), describes a method for differentiating the unique letter characters of similar drug names known to have been confused with one another. Starting with a drug name printed in lowercase letters, tall man lettering highlights the differences between similar drug names by capitalizing dissimilar letters. Accentuating a unique portion of a drug name with uppercase letters along with other means, such as color, bolding, or contrast, 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.

ISMP list. Since 2008, ISMP has maintained a list of drug names with recommended, bolded tall man letters. The list includes mostly generic-generic drug name pairs, although a few brand-brand or brand-generic name pairs are included. 

While numerous studies between 2000 and 2016 have demonstrated the ability of tall man letters alone or in conjunction with other text enhancements to improve the accuracy of drug name perception and reduce errors due to drug name similarity,5,7-14 some studies have suggested that the strategy is ineffective.15-17  The evidence is mixed due in large part to methodological differences and significant study limitations (see the sidebar in right column of PDF version). Nevertheless, while gaps still exist in our full understanding of the role of tall man lettering in the clinical setting, there is sufficient evidence to suggest that this simple and straightforward technique is worth implementing as one of numerous strategies to mitigate the risk of errors due to similar drug names. To await irrefutable, scientific proof of effectiveness minimizes and undervalues the study findings and anecdotal evidence available today18 that support this important risk-reduction strategy. As such, the use of tall man letters has been endorsed by The Joint Commission (recommended, not required), the US Food and Drug Administration (FDA) (as part of its Name Differentiation Project), as well as other national and international organizations, including the World Health Organization and the International Medication Safety Network (IMSN).6,19

Periodically, ISMP updates its list of drug name pairs with recommended bolded, tall man letters. The update includes analyses of reported incidents from our error databases, a survey of practitioners on the topic, and an internal assessment of drug name pairs that would benefit from the application of bolded, tall man lettering. The internal assessment includes an exploration of orthographic similarity; patterns of similarities in dosage, form, and use; and the potential for (or actual) patient harm if the drugs are confused.

ISMP survey. ISMP conducted a survey on drug name pairs with tall man letters between February and April 2016 and received 235 responses. The findings from the survey and a discussion of how we update the ISMP list follow.

Scope and effectiveness of tall man letters. Eighty percent or more of the respondents reported that their facility uses tall man lettering for similar drug names that appear on prescriber and pharmacy computer drug selection screens, automated dispensing cabinet (ADC) screens, and computer-generated pharmacy labels. Between 73% and 79% of respondents use tall man lettering for similar drug names that appear on medication administration records (MARs), standard order sets, smart pump drug library screens, shelf/bin labels, and policies/protocols. This represents a significant increase in usage of tall man lettering since our prior survey in 2010. All areas of implementation increased by approximately 50% or more, and usage with prescriber computer drug selection screens, order sets, and smart pumps increased by at least 80% (see Table 1). However, there were multiple respondents who reported that their technology systems did not allow them to change the case of letters in drug names, use mixed case letters, or bold the tall man letters—an additional text enhancement for tall man letters that ISMP recommends.

Between two-thirds and three-quarters of respondents thought that tall man lettering has been effective in reducing the risk of errors due to look-alike drug names, with the exceptions of tall man lettering used in policies and protocols and smart infusion pump screens. While some respondents were undecided about the effectiveness of tall man letters, very few felt tall man letters were wholly ineffective in reducing errors (see Table 1).

Internal selection of name pairs for tall man letters. For respondents who use tall man letters, most (51%) told us they employ this strategy for more than 30 drug name pairs; 41% use it for 11-30 pairs; and 8% use it for 10 or fewer drug name pairs. This represents a 38% increase since 2010 in employing tall man letters for more than 30 drug name pairs. Most respondents have built their list of drug name pairs with tall man letters utilizing resources such as the ISMP list, FDA list, internal risk and error data, and drug information vendors. Most respondents (85%) use tall man lettering that complies with the ISMP and FDA recommended configurations.

Communication of name pairs with tall man letters. The purpose and intended use of name pairs that require tall man letters are communicated to staff primarily via policy statements (48%); inservices, educational programs, and orientation (39%); memos and posters (35%); and staff meetings (35%). Posting on an Intranet site and providing emails were also listed as ways to educate staff about tall man letters. However, 1 in every 5 respondents did not know how the purpose and use of tall man letters has been communicated to staff. Some respondents reported that their use has been integrated into the system without explanation. Providing education to practitioners about the purpose of tall man lettering is key, as the use of tall man letters to differentiate drug names is more successful to those who are aware of its purpose.8 A few respondents commented that physicians are confused about tall man letters, while others noted that physicians have told them they find the tall man lettering helpful when making drug selections.

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, about 86% of respondents felt that the use of tall man letters by the pharmaceutical industry helps to reduce drug selection errors. More compelling is the fact that approximately half (52%) of the 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 numerous examples of look-alike name pairs involved in these potential events, the most common of which were hydrALAZINE and hydrOXYzine, vinCRIStine and vinBLAStine, levETIRAcetam and levoFLOXacin (a new name that will be added to the ISMP list), and OxyCONTIN, oxyCODONE, and HYDROcodone. Several respondents reported that they frequently hear from physicians, medical residents, pharmacy students, and/or nurses, that the use of tall man letters, particularly for opioids, has helped them avoid errors when selecting drugs during order entry, removing medications from an ADC via override, and prior to drug administration when referencing the MAR.

In addition to distinguishing portions of drug names that are dissimilar, tall man letters were often reported by respondents as an effective alert system that quickly captured their attention and caused them to pause, read the drug name more carefully a second time, and make sure the drug was appropriate for the patient. The presence of the tall man letters made staff aware of the possibility of an error, causing them to take steps not otherwise taken, such as reading through an entire pick list or verifying the drug a second time, to ensure they have the correct drug. Respondents referred to the tall man letters as a “visual alert system” and a “subconscious cue” that help to “refocus the eye” and “slow down or stop the process” to ensure they have the correct drug. They reported that the tall man letters serve as a reminder that the drug has been confused with another medication with a look-alike name, causing them to pay more attention to the spelling of the medication. As one respondent commented, “I train myself to search for tall man letters when verifying medications, and have prevented errors by focusing on these different letters for drugs with similar names.” Another respondent noted, “When I see the tall man lettering, it alerts me that a look- or sound-alike drug is being dispensed, so I make a point of verifying the indication of the drug to be sure I have selected the correct one.” 

Also, several managers indicated seeing reports of close calls in which tall man letters had helped to prevent or detect medication errors. A few others reported that analyses of wrong drug selection errors in their facilities show fewer safety reports for medications that use tall man letters than those that do not—the latter names are then reviewed for possible tall man letters. Some respondents also reported seeing a decrease in errors after implementing tall man letters; however, as one respondent pointed out, many times other strategies are also implemented to reduce the risk of mix-ups, so the effect may be related to a “bundle” of risk-reduction strategies, one of which is the use of tall man letters. Other risk-reduction strategies may include: preventing the consecutive appearance of potentially confusable drug names on screens; including both the brand and generic names for redundancy; including the indication with orders and prescriptions; storing products with look-alike names in different locations; and implementing drug-specific strategies such as stocking different forms or strengths of medications with similar names. 

While more than one-third of respondents (37%) could not say with certainty that tall man lettering had helped them avoid an error, only 10% felt that their use was not helpful. Among these respondents, two suggested that tall man lettering has become antiquated given current technologies, particularly barcode scanning.

Update of ISMP’s list. One of the primary reasons for conducting this survey was to utilize the findings to update ISMP’s current list of look-alike drug name pairs with tall man letters. We believe healthcare practitioners should be involved in the process of identifying confusable drug name pairs relevant to their respective practice settings, and reviewing proposed tall man lettering for possible implementation. The capitalized letters should make the drug names distinguishable from the user’s perspective.

In the survey, we listed 16 potential new drug name pairs or trios, or single drug names that may be confused with another drug name pair already on the list. Of these, at least half or more of the respondents felt that 13 of these should be added to the ISMP list of drug names with tall man letters (see Table 2). For these 13 name pairs or trios, we evaluated the potential for overlap among indications for use, frequency of use, form of the drug, and available strengths, along with the potential for harm if a mix-up occurred. Based on this assessment, all 13 drug name pairs or trios were added to the ISMP list. The 3 name pairs in our survey that were not added to the list include:  dexameTHASONE and dexmedeTOMidine; zolPIDEM (and ZOLMitriptan already on the list with SUMAtriptan); and oxyBUTYnin (and oxyCODONE already on the list with HYDROcodone and OxyCONTIN).

Many respondents shared their thoughts regarding other drug name pairs that were not included in the survey. We reviewed each suggestion carefully 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 no longer appear novel.6 More than 60 name pairs with tall man letters were suggested (many brand names, which we hesitate to include without FDA approval). There were 5 pairs that were closely associated with high risk of harm and, thus, were added to the list:

  • HYDROXYprogesterone (and medroxyPROGESTERone already on the FDA list) 
  •  miFEPRIStone and miSOPROStol
  • metyroSINE and metyraPONE
  • hydroCHLOROthiazide (and hydrOXYzine/hydrALAZINE already on the FDA list)
  • raNITIdine and riMANTAdine

 Table 3 (below) provides an updated ISMP list of drug name pairs with tall man letters, with the new additions or changes in the tall man lettering scheme highlighted in red. By early next week, the FDA and ISMP Lists of Look-Alike Drug Names with Recommended Tall Man Letters will also be updated on our website to reflect these changes (

Standardization of tall man letters. To promote standardization regarding which letters to present in uppercase, ISMP follows a tested methodology whenever possible called the CD3 rule.20 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 scheme provided by FDA and ISMP be followed to promote consistency.


  1. Lambert BL, Lin SJ, Tan H. Designing safe drug names. Drug Saf. 2005;28(6):495–512.
  2. Lambert BL, Schroeder SR, Galanter WL. Does tall man lettering prevent drug name confusion errors? Incomplete and conflicting evidence suggest need for definitive study. BMJ Qual Saf. 2016;25(4):213-7.
  3. Flynn EA, Barker KN, Carnahan BJ. National observational study of prescription dispensing accuracy and safety in 50 pharmacies. J Am Pharm Assoc (Wash). 2003;43(2):191–200.
  4. Cina JL, Gandhi TK, Churchill W, et al. How many hospital pharmacy medication dispensing errors go undetected? Jt Comm J Qual Patient Saf. 2006;32(2):73–80.
  5. DeHenau C, Becker MW, Bello NM, Liu S, Bix L. Tallman lettering as a strategy for differentiation in look-alike, sound-alike drug names: the role of familiarity in differentiating drug doppelgangers. Appl Ergon. 2016;52:77-84.
  6. ISMP Canada. Principles for the application of tallman lettering in Canada. October 2015.
  7. Filik R, Purdy K, Gale A, Gerrett D. Drug name confusion: evaluating the effectiveness of capital (“tall man”) letters using eye movement data. Soc Sci Med. 2004;59(12):2597-601.
  8. Filik R, Purdy K, Gale A, Gerrett D. Labeling of medicines and patient safety: evaluating methods of reducing drug name confusion. Hum Factors. 2006;48(1):39-47.
  9. Grasha A. Cognitive systems perspective on human performance in the pharmacy: implications for accuracy, effectiveness, and job satisfaction (Report No. 062100). Alexandria (VA): NACDS. 2000.
  10. Darker IT, Gerret D, Filik R, Purdy KJ, Gale AG. The influence of ‘tall man’ lettering on errors of visual perception in the recognition of written drug names. Ergonomics. 2011;54(1):21–33.
  11. Or CK, Chan AH. Effects of text enhancements on the differentiation performance of orthographically similar drug names. Work. 2014;48(4):521–8.
  12. Or CK, Wang H. A comparison of the effects of different typographical methods on the recognizability of printed drug names. Drug Saf. 2014;37(5):351–9.
  13. Filik R, Price J, Darker I, Gerrett D, Purdy K, Gale A. The influence of tall man lettering on drug name confusion: a laboratory-based investigation in the UK using younger and older adults and healthcare practitioners. Drug Saf. 2010;33(8):677–87.
  14. Gabriele S. The role of typography in differentiating look-alike/sound-alike drug names. Healthc Q. 2006; 9(Spec No):88-95.
  15. Schell KL. Using enhanced text to facilitate recognition of drug names: evidence from two experimental studies. Appl Ergon. 2009;40(1):82–90.
  16. Irwin A, Mearns K, Watson M, Urquhart J. The effect of proximity, tall man lettering, and time pressure on accurate visual perception of drug names. Hum Factors. 2013;55(2):253–66.
  17. Zhong W, Feinstein JA, Patel NS, Dai D, Feudtner C. Tall man lettering and potential prescription errors: a time series analysis of 42 children’s hospitals in the USA over 9 years. BMJ Qual Saf. Published Online First: November 3, 2015.
  18. Leape LL, Berwick MB, Bates DW. What practices will most improve safety? Evidence-based medicine meets patient safety. JAMA. 2002;288(4):501-7.
  19. Position statement on improving the safety of international non-proprietary names of medicines (INNs). Horsham (PA): International Medication Safety Network; November 2011.
  20. Gerrett D, Gale AG, Darker IT, Filik R, Purdy KJ. Tall man lettering. Final report of the use of tall man lettering to minimise selection errors of medicine names in computer prescribing and dispensing systems. Loughborough University Enterprises Ltd; 2009.  
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