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


Background: Medication errors commonly involve confusion between drugs with similar names. One possible method of reducing error is to emphasize differences between the names using ‘Tall Man’ (uppercase) letters (e.g. cef-TAZidime vs cefUROxime). Previous studies investigating this issue have been conducted mainly on university students, and results have been mixed.

Objective: To investigate the influence of Tall Man lettering on drug name confusion in other key participant groups.

Study Design: Two separate experiments were conducted. In Experiment 1 (conducted at the University of Glasgow, Scotland, between January 2008 and May 2008), younger and older adults performed a same/different judgement task. In Experiment 2 (conducted at various sites in England between December 2008 and February 2009), healthcare practitioners performed a task based on electronic prescribing.

Results: In Experiment 1, both younger and older adults made fewer name confusion errors when names contained Tall Man letters. Response times suggested that Tall Man lettering drew participants’ attention to those letters, but that readers did not solely rely on these letters in making their response. In Experiment 2, healthcare practitioners made fewer name confusion errors when the names contained Tall Man letters.

Conclusions: Overall, results showed that Tall Man lettering reduced drug name confusion errors in a series of laboratory-based tasks, in both younger and older adults, and healthcare practitioners. Thus, the current findings offer some support for the use of Tall Man letters as a possible systems change that could be made by both pharmacies and manufacturers in an effort to reduce error caused by drug name confusion.

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  1. 1.

    1Pilot data were collected from a small sample of older adults in order to determine a display time that would equate overall accuracy across age groups, so that patterns of performance could be compared on the same point of the performance scale (i.e. so that older adults were not simply performing at chance level).

  2. 2.

    2Because of high accuracy scores, in order to reduce the likelihood of a ceiling effect, additional analyses were carried out on a dataset where participants who had scored over 95% correct in all conditions had been removed, resulting in a reduced dataset of 75 participants. Findings were essentially the same as those for the full set of participants. In particular, there was still a significant interaction, F(1 ,74) = 6.99, p < 0.05, $ða_⤪ p^2$ = 0.09, indicating that when the target was absent from the list, participants were less likely to indicate that the target was present (i.e. to confuse a similar distractor for the target) when the name contained Tall Man lettering: F(1,74) = 14.06, p< 0.001, $ða_⤪ p^2$ = 0.16. In contrast, when the target was present, there was no difference between the two conditions: F < 1. This would suggest that significant effects were not simply due to the reduced variance associated with high accuracy scores.


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No funding was received for the conduct of Experiment 1. Experiment 2 was supported by funding from the UK NHS Connecting for Health initiative. The funding organization specified the issue to be investigated and advised on drug names that are often involved in error, but were otherwise not involved in the conduct of the study, interpretation of results or preparation of the manuscript. David Gerrett received consultancy remuneration to undertake specific tasks for this research. He continues to collaborate with the research team and is now working with the National Patient Safety Agency, which has an interest in furthering knowledge in this area. All other authors have no potential conflicts of interest to declare that are directly relevant to the content of this study.

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Correspondence to Dr Ruth Filik.

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Instructions for Producing CD3-Type Tall Man Drug Names

To apply the CD3 Tall Man rule, firstly collect drug names into groups of two or more names that are orthographically similar (in our case, groupings were determined in consultation with the NPSA and NHS Connecting for Health initiative). Then, on a letter-by-letter basis, start from either end of each drug name and work towards the middle; the first letters encountered at either end that differ across at least two drug names in the group, along with all letters occurring between them, are deemed to fall within a critical portion of each drug name and are candidates for capitalization. Capitalize a maximum of only three of these letters per drug name. Where more than three letters are present in the critical portion of the drug name, capitalize the centre most three. Where this would result in letters that are common amongst all the drug names of the group in those positions being capitalized, then capitalize the next most peripheral letters that differ across at least two drug names. The initial letters of proprietary drug names are always capitalized. In order to prevent confusion with a lowercase letter ‘l’ and the capital letter ‘I’, the lowercase letter ‘i’ is not capitalized unless it was the initial letter of a proprietary drug name. Using the CD3 rule, cefixime, cefotaxime, ceftazidime, and cefuroxime would become cefiXime and cefOTAxime, cefTAZidime, cefUROxime.

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Filik, R., Price, J., Darker, I. et al. The Influence of Tall Man Lettering on Drug Name Confusion. Drug-Safety 33, 677–687 (2010).

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  • National Health Service
  • Simple Main Effect
  • Chlorpropamide
  • Healthcare Practitioner
  • Natural Case