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Use of Tall Man Letters is Gaining Wide Acceptance

ISMP extends sincere thanks to all who completed our recent survey1 on the use of tall man letters to differentiate products with look-alike names. Tall man letters are uppercase letters that are used within a drug name to highlight its primary dissimilarities with look-alike drug names. Several studies have shown that: 1) highlighting sections of words using tall man lettering can make similar drug names easier to distinguish2, and 2) fewer errors are made when tall man letters are used to differentiate products with look-alike names.3-4 ISMP5-7, FDA8, The Joint Commission9, and other safety-conscious organizations such as the National Association of Boards of Pharmacy10 have promoted the use of tall man letters as one means of reducing confusion between similar drug names. From the 451 survey responses we received, it appears that the vast majority of respondents agreed. Nearly all (87%) felt that the use of tall man letters by the medical product industry helps to reduce drug selection errors, and two-thirds (64%) reported that tall man lettering has actually prevented them from dispensing or administering the wrong medication.

Scope and effectiveness of tall man letters

Approximately half of all respondents reported using tall man letters in conjunction with pharmacy-generated product and shelf labels, computer screens, and medication administration records (MARs) (see Table 1). Tall Man LettersHalf to three-quarters of respondents who used tall man letters with look-alike drug name pairs felt that this strategy was effective in reducing the risk of errors, depending on where it was used. Use on computer-generated pharmacy labels was the most prevalent and felt to be the most effective, while use on preprinted order forms was among the least prevalent and considered least effective. In general, between a quarter and a third of respondents were undecided about the effectiveness of tall man letters, but very few reported that tall man letters were wholly ineffective in reducing the risk of errors. Use of tall man letters was less widely reported for medications listed on prescriber order entry screens and smart pump libraries.

For respondents who use tall man letters, 40% are using this error-reduction strategy for 1-16 drug name pairs; 28% are using it for 17-25 name pairs; 18% for 26-36 name pairs; and 14% for more than 36 drug name pairs. Table 2 Drug Name Pairsprovides information on the use of tall man letters for the specific drug name pairs in the FDA Name Differentiation Project8 and/or those selected by the hospital. Three-quarters (78%) of respondents who use tall man letters for look-alike drug name pairs have included all or some of the FDA name pairs; however, 20% were not sure if their list of drug name pairs included any or all of the FDA name pairs, thus implying awareness of the FDA Name Differentiation Project may not be widespread among practitioners.

Methods of expressing letter characters

When respondents were asked to rank various methods of distinguishing unique letter characters in look-alike name pairs, the use of uppercase letters (i.e., tall man letters) was, by far, the most prevalent first choice. Other methods were ranked in the following order: font differentiation, color background, italics, underline, and reverse print (e.g., dark background with white lettering). Some respondents also suggested using bold letters and enlarging the font size to help practitioners distinguish between products with look-alike names.

Tall man lettering with specific name pairs

Three-quarters (76-77%) of respondents agreed that the tall man letters suggested in the survey for NovoLOG and NovoLIN, and HumaLOG and HumuLIN, helped differentiate these products. About two-thirds (60-66%) of respondents agreed that tall man letters helped to prevent mix-ups between: oxyCODONE and OxyCONTIN; ceFAZolin and cefTRIAXONE; and FLUoxetine and DULOXetine. There was only one drug name pair in the survey that less than half of the respondents felt was effective: clonazePAM and LORazePAM. Respondents who suggested an alternative often left the “PAM” part of both drug names in small letters, suggesting that drawing attention to “PAM” in both drug names could contribute to sameness (see Table 3).

effectiveness of tall man letters

ISMP list of name pairs with tall man letters

One of the primary reasons for conducting this survey was to use the findings to prepare an unofficial list of look-alike drug name pairs with suggested tall man letters to guide practitioners and healthcare organizations. This is not intended to replace drug name safety testing to prevent name similarities before marketing a product. Many respondents shared their thoughts about other drug name pairs that might benefit from using tall man letters that were not included in our survey. We reviewed each suggestion very carefully, placing emphasis on the potential for patient harm, the frequency of use for each medication, and the need to keep the list short enough to avoid diluting the effectiveness of tall man letters. Table 4 Drug Name Pairs Tall Man Lettersprovides the FDA list of generic drug names with tall man letters as well as a list of the drug name pairs for which ISMP recommends the use of tall man letters.

One of the difficulties with the use of tall man letters is the lack of standardization regarding which name pairs to include as well as which letters to present in uppercase. While there is some evidence to support the use of tall man letters to reduce the risk of confusion between look-alike drug names2-4, little evidence is available regarding which of the dissimilar letters in each drug name should be highlighted. To help promote standardization, ISMP suggests that the tall man lettering scheme provided by FDA and ISMP for the drug name pairs listed in Table 4 be followed consistently.

ISMP is very interested in any thoughts you have regarding the list of drug name pairs found in Table 4 for which tall man letters are recommended. Please send your comments to [email protected]. As you have consistently shown, you can make a difference!


  1. ISMP. Survey on tall man lettering to reduce drug name confusion. ISMP Med Saf Alert! 2008;13(10):4.
  2. Filik R, Purdy K, Gale A, Gerrett D. Drug name confusion: evaluating the effectiveness of capital (“Tall Man”) letters using eye movement data. Social Science & Medicine 2004;59(12):2597-2601.
  3. Filik R, Purdy K, Gale A, Gerrett D. Labeling of medicines and patient safety: evaluating methods of reducing drug name confusion. Human Factors 2006;48(1):39-47.
  4. Grasha A. Cognitive systems perspective on human performance in the pharmacy: implications for accuracy, effectiveness, and job satisfaction. Alexandria (VA): NACDS; 2000 Report No. 062100.
  5. ISMP. What’s in a name? Ways to prevent dispensing errors linked to name confusion. ISMP Med Saf Alert! 2002;7(12):1-3.
  6. ISMP. Draft guidelines for safe electronic communication of medication orders. ISMP Med Saf Alert! 2003;8(4):3-4.
  7. ISMP. Let us know if “tall man” letters have been effective. ISMP Med Saf Alert! 2003;8(19):3.
  8. FDA. Name differentiation project. Center for Drug Evaluation and Research. 2002; 
  9. The Joint Commission. NPSG: Identify and, at a minimum, annually review a list of look-alike/sound-alike drugs used in the organization, and take action to prevent errors involving the interchange of these drugs.
  10. National Association of Boards of Pharmacy. “TALL MAN” letter utilization for look-alike drug names. 2008.