Tall Man Lettering: The FDA and ISMP Lists

Tall man lettering is a name-differentiation convention, not a single standard. Two lists exist, they are maintained separately by two different organisations, and they do not match. The US Food and Drug Administration publishes a short list of established (generic) drug names it recommends be printed with tall man letters, under its Name Differentiation Project. The Institute for Safe Medication Practices publishes a longer list that reproduces the FDA names in one table and then adds a second, larger table of its own recommendations, which ISMP states plainly is not an official FDA-approved list. Treating the two as one merged standard is the first mistake a medication-safety programme makes, because it obscures which entries carry regulatory weight over a manufacturer’s label and which are voluntary conventions you are choosing to apply inside your own systems.

This page is written for the people who own that decision at an institution: medication-safety officers, pharmacy informatics, P&T committees, patient-safety and quality directors. It covers what the two lists actually are, the published rule for deciding which letters get capitalised, how to apply the convention consistently across the five or six surfaces where a drug name is displayed, and — because it matters for how much effort you spend — an honest account of what the experimental evidence does and does not show.

Scope note: this is operational guidance for professional medication-safety practice. The drug names below appear only as examples of the lettering convention as published by FDA and ISMP. Nothing here is advice about taking, prescribing, or substituting any medicine.

The two lists are different documents, and the difference is load-bearing

FDA’s list: the Name Differentiation Project

FDA initiated the Name Differentiation Project in 2001 to evaluate postmarketing reports of name-pair confusion and decide whether tall man lettering should be applied to differentiate similar established names. FDA’s stated evaluation criteria are the degree of similarity between the name pair, the safety risk if the two are confused, overlapping product characteristics, reports of wrong-drug errors, and the causes or contributing factors behind them.

The mechanism matters. When FDA concludes tall man lettering is the right response, it requests that the manufacturer voluntarily revise its labels and labeling, then updates the published list. It is not a rule, it is not codified, and there is no enforcement action attached to it. FDA’s page (content current as of 12 June 2026) states the convention as: starting on the left side of a drug name, capitalise dissimilar letters — the examples FDA itself gives are vinBLAStine versus vinCRIStine and CISplatin versus CARBOplatin.

The FDA list is short. As published, it covers roughly two dozen name groups spanning about 43 established names, all of them generic. It is a free, ungated web page, which is the single most practical thing about it: anyone on your team can read the authoritative source in a browser without a login.

ISMP’s list: broader, voluntary, and separately maintained

ISMP has maintained its own list since 2008. The current published document — FDA and ISMP Lists of Look-Alike Drug Names with Recommended Tall Man (Mixed Case) Letters — is deliberately structured in two parts:

Table 1 is the FDA-approved list of established generic names, reproduced.
Table 2 is ISMP’s list of additional drug names. ISMP states directly that this “is not an official list approved by FDA” and that it is “intended for voluntary use by healthcare practitioners, drug information vendors, and medication technology vendors,” noting that any product label change by a manufacturer still requires FDA approval.

Table 2 is several times the size of Table 1 and differs in kind, not just in length. It includes brand–brand and brand–generic pairs, which FDA’s list does not: CeleBREX and CeleXA, ZyPREXA and ZyrTEC, HumaLOG and HumuLIN, NovoLIN and NovoLOG, PriLOSEC and PROzac, LaMICtal and LamISIL, SandIMMUNE and SandoSTATIN, NexAVAR and NexIUM, DEPO-Medrol and SOLU-Medrol and Solu-CORTEF. ISMP flags brand names with a marker in its own document precisely because some brand names carry tall man letters in their opening characters and are not obviously brand names on sight.

Concrete places the two lists diverge

These are not hypothetical. Reading both published sources side by side:

Grouping differs. FDA’s page lists Hydralazine and Hydroxyzine as a pair, and lists HYDROmorphone on its own with no confusion partner named. ISMP’s rendering of the same FDA table presents hydrALAZINE, HYDROmorphone and hydrOXYzine as a three-way group.
Orphan entries. mitoXANTRONE appears on FDA’s list with no partner named; ISMP’s Table 1 records the partner as “Not specified” and then pairs mitoXANTRONE with mitoMYcin in Table 2 — an ISMP recommendation, not an FDA one.
Dead weight. Three names on the FDA list are flagged by ISMP as discontinued and not marketed in the United States: acetoHEXAMIDE, sulfiSOXAZOLE and TOLBUTamide. If you build a formulary rule straight from the FDA list, you will be maintaining tall man configuration for products you do not stock.
Cross-table repetition. Several names appear in both tables with different partners — cycloSERINE and cycloSPORINE are an FDA pair, but ISMP’s Table 2 adds cycloPHOSphamide to the group. niCARdipine and NIFEdipine are FDA; ISMP adds niMODipine. sulfADIAZINE is paired with sulfiSOXAZOLE by FDA and with sulfaSALAzine by ISMP.

The operational consequence: when you write your policy, state which list you have adopted and to what extent. “We apply the FDA list plus the ISMP additional list in full” and “we apply the FDA list plus a locally selected subset of the ISMP list” are both defensible positions. “We use tall man lettering” is not a position — it is an ambiguity that shows up two years later as an inconsistency between pharmacy and nursing systems that nobody can explain.

Which letters get capitalised: the CD3 rule

The letters are not chosen by eye. ISMP states that, to promote standardisation about which letters appear in uppercase and bold, it follows a tested methodology called the CD3 rule wherever possible, attributed to the 2009 Loughborough University Enterprises final report on tall man lettering by Gerrett, Gale, Darker, Filik and Purdy, produced to address selection errors in computer prescribing and dispensing systems.

As ISMP describes it, the method has three moves:

Work from the left. Once two or more dissimilar letters are encountered, capitalise all characters to the right of that point.
Then work back from the right. Return two or more letters that are common to both names to lowercase.
Handle the no-common-suffix case. When the rule cannot be applied because there are no common letters on the right-hand side of the name, capitalise the central part of the word only.

ISMP adds an explicit escape hatch: when applying the rule fails to produce the best result — because it makes the names look too similar, or makes them hard to read given how they are pronounced — an alternative option is considered instead.

You can see all three shapes in the published lists:

Shared prefix and shared suffix gives a capitalised middle: vinBLAStine and vinCRIStine share “vin” at the front and “tine” at the back, so only the differentiating core is raised.
Shared prefix, nothing shared at the end gives a capitalised tail: chlorproMAZINE and chlorproPAMIDE.
Nothing shared at the front means capitalisation starts at character one: CISplatin and CARBOplatin, DOBUTamine and DOPamine.

Do not re-derive the string — copy the published one

This is the practical rule that saves the most trouble. The published forms contain results a naive reading of CD3 would not produce, because ISMP’s escape hatch has been exercised. rOPINIRole carries a lowercase opening character followed by a capitalised block and a lowercase tail. HYDROmorphone, medroxyPROGESTERone, methylPREDNISolone and methylTESTOSTERone each sit in a three-way group where the capitalisation was chosen for the group, not for a single pairwise comparison. ISMP explicitly asks that the schemes provided by FDA and ISMP be followed for the names on the lists, in order to promote consistency.

So: your configuration source should be the published string, character for character, from whichever list you adopted. A locally invented tall man form for a name pair that is not on either list is a legitimate local decision — hospitals do add pairs from their own event data — but it should be recorded as a local addition, run through CD3 deliberately, and reviewed for whether it makes the names look more alike rather than less.

Applying it across every surface where a drug name is displayed

A drug name is displayed to a clinician in at least eight distinct places, each rendered by a different system with its own field definitions. ISMP’s 2016 practitioner survey (235 respondents) measured adoption by surface, and the comparison against its 2010 survey shows both the direction of travel and the surfaces that lag:

Surface	Using tall man letters (2010)	Using tall man letters (2016)	Rated effective (2016)
Pharmacy computer drug selection screens	54%	83%	73%
Prescriber computer drug selection screens	44%	82%	64%
Automated dispensing cabinet (ADC) screens	53%	80%	67%
Computer-generated pharmacy labels	55%	80%	72%
Electronic medication administration records (eMARs)	50%	79%	65%
Standard order sets	43%	78%	62%
Smart pump drug libraries	42%	77%	55%
Shelf and bin labels	51%	75%	65%
Policies and protocols	—	73%	44%

Two things are worth reading out of that table. First, adoption rose on every surface, by roughly half again or more, and by at least 80% on prescriber selection screens, order sets and smart pumps. Second, and more usefully for planning: the surfaces where the convention is rated least effective are the ones furthest from the moment of selection — policies and protocols at 44%, smart pump libraries at 55%. Tall man lettering earns its keep at the point where a human is picking one name out of a list of similar names. In a document nobody reads at the bedside, it is decoration.

The technical defeats — where it silently fails

The same ISMP survey recorded the failure mode directly: multiple respondents 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 — bolding being an additional enhancement ISMP recommends alongside the capitalisation. This is the part that a policy decision cannot fix, and it is why the rollout has to be run surface by surface rather than announced once.

The recurring mechanisms to test for, in the order they usually bite:

Forced case normalisation. A display field or print template that upper-cases or lower-cases the whole name on render destroys the convention while leaving the record itself correct. The database is right and the screen is wrong, so an audit of the drug file passes.
Character limits and truncation. ADC screens, pump library entries, shelf tags and small-format labels are frequently the tightest fields in the estate. If the differentiating block sits past the truncation point, the tall man letters are configured and invisible. Test the longest names, not a representative one: HYDROXYprogesterone, medroxyPROGESTERone, methylTESTOSTERone, hydroCHLOROthiazide and idaruCIZUmab are useful stress cases.
Case-insensitive search that also case-normalises the result. Searching should of course be case-insensitive; the defect is when the returned pick-list is rendered in normalised case. Separately, ISMP recommends configuring computer systems to require a minimum of the first five letters of a drug name during product searches — a three-character search on a look-alike prefix returns exactly the ambiguous set tall man lettering is trying to disambiguate.
Interface feeds that re-derive the display name. Where the EHR, the ADC, the pump library and the labelling system each receive the drug file through a different interface, one of them is usually rebuilding the display string from a source field rather than carrying the formatted name through. That is the classic reason pharmacy screens show tall man letters and ADC screens do not.
Vendor content that overwrites local edits. Drug information vendor updates can revert locally applied formatting on the next content load. If your tall man configuration lives in a field the vendor also populates, it needs to be re-verified after each content update, not once at go-live.
Bolding as a separate capability. Several surfaces support mixed case but not bold. That is a partial implementation, not a failure — but record it, because the published lists specify bolded tall man letters and your policy should say which surfaces achieve the full rendering.

A per-surface verification pass

Rather than asking “have we implemented tall man lettering,” verify each surface independently with a fixed test set. Choose five to ten name groups from your adopted list that you actually stock — including at least one long name and one three-way group — and then, for each surface, confirm on the live screen or a printed sample that: the name renders in mixed case; the capitalised block matches the published string exactly; nothing is truncated before the end of the capitalised block; the bold enhancement is present if the surface supports it; and searching by the first five characters returns the group rather than a single name. Record the result per surface, including the ones that fail, and re-run the pass after any EHR upgrade, drug file content load, or ADC or pump library rebuild. This is the kind of narrow, repeatable check that belongs in a performance improvement project — see the PDSA cycle and Model for Improvement for the structure, and how a PIP write-up is assembled for documenting it.

Why partial adoption is a failure mode in its own right

The argument for a full-estate rollout is not tidiness. It is that the convention works by signalling, and a signal that appears on some screens and not others stops carrying information.

When tall man lettering is applied consistently, the absence of capitals on a name is itself meaningful: it tells the person selecting that this name is not on the confusable list. When it is applied on the pharmacy screen but not the ADC screen, that inference is false on the ADC screen — and a clinician who has learned to rely on the cue in one place will carry the habit to the place where it does not hold. Inconsistency across systems does not merely fail to help; it makes an unreliable cue available to be trusted.

ISMP’s survey found a related and underappreciated problem on the human side: one in every five respondents did not know how the purpose and use of tall man letters had been communicated to staff, and some reported that the convention had been “integrated into the system without explanation.” That matters because the underlying research is fairly clear that awareness of the purpose is part of the mechanism — Filik and colleagues in 2006 found tall man letters made look-alike names easier to distinguish when participants were aware of what the capitals were for, and a later analysis framed the effect as combining a bottom-up visual pull with a top-down, feature-based attention set that only a practitioner who knows the convention can adopt. A silent rollout removes half the mechanism and then measures the result.

Tall man lettering is also explicitly one layer among several. ISMP’s own guidance alongside the confused-names list recommends using both brand and generic names on prescriptions and labels, including the purpose of the medication on the prescription, requiring a minimum of the first five letters during product searches, and changing the appearance of look-alike names. Its 2016 commentary adds: preventing potentially confusable names from appearing consecutively on a selection screen, storing look-alike products in different locations, and stocking different forms or strengths of similarly named products. A programme that ships lettering and nothing else has implemented the cheapest element of the bundle. Related institutional controls sit in medication reconciliation at transitions of care and in medication use evaluation where a specific drug’s real-world use is audited against criteria.

The evidence, stated honestly

Tall man lettering is widely endorsed. ISMP records endorsement by itself, by The Joint Commission, by FDA through the Name Differentiation Project, and by other national and international bodies including the World Health Organization and the International Medication Safety Network.

One widely held belief is wrong and worth correcting inside your own institution: The Joint Commission recommends tall man lettering, it does not require it. ISMP states the position explicitly — recommended, not required — and goes further, noting that tall man lettering “was never required by any standards or regulatory agency.” Look-alike/sound-alike medications have featured in accreditation expectations as a category, but that is not the same as a mandate to use this particular typographic convention. If your policy justifies the programme by citing a requirement that does not exist, it will not survive contact with a surveyor asking which standard. On what the Goals do and do not say, see National Patient Safety Goals.

What supports it

A substantial body of work between 2000 and 2021 found tall man letters, alone or with other text enhancements, improved the accuracy of drug name perception or reduced confusion. Grasha’s 2000 study for the National Association of Chain Drug Stores was the first to show reduced selection errors in a simulated pharmacy dispensing environment. Filik and colleagues found reduced confusion during a search of complex drug labels using eye-movement data in 2004, and in 2010 found that both laypeople and healthcare professionals performing an electronic-prescribing-based task made fewer errors when names carried tall man letters. Darker and colleagues in 2011 found improved accuracy of name perception among prescribers who knew the purpose of the convention. Wang, Tao and Yan published a systematic review and meta-analysis of text enhancement in 2021.

What does not

Several studies found no benefit, and one found a cost. Schell in 2009, working with university students who were not health professionals, found tall man lettering had no effect on drug name recognition and produced an increase in false alarms — participants judging names to be different when they were the same. Irwin and colleagues in 2013 examined tall man lettering alongside proximity and time pressure on accurate visual perception of drug names. Most consequentially, Zhong and colleagues published a time-series analysis in BMJ Quality & Safety in 2016 covering 42 children’s hospitals over nine years and found no significant reduction in potential prescription errors associated with tall man lettering. In the same issue, Lambert, Schroeder and Galanter published an editorial whose title is the fairest one-line summary of the field: incomplete and conflicting evidence suggests the need for a definitive study.

The caveats that cut both ways

Three qualifications should shape how much weight you put on any of it.

Most of the supportive evidence is laboratory work. ISMP acknowledges this directly — the studies’ most notable limitation is their performance in a laboratory setting rather than a real clinical one. Improved discrimination in a name-matching task is not the same as fewer wrong-drug administrations on a ward.
The mechanism may not be the one assumed. Darker and colleagues found a similar benefit when the entire drug name was presented in capitals, which suggests the advantage may relate to letter size and salience rather than to highlighting the specific differentiating portion. If that is right, then getting the exact CD3 characters correct matters less than making the name stand out at all — though consistency with the published lists remains the right operational choice.
The negative studies have limitations too. ISMP’s critique of Zhong is substantive rather than defensive: the analysis could not establish whether or when each of the 42 hospitals had actually implemented tall man lettering for the pairs under study, so a null result may reflect non-implementation rather than ineffectiveness; seven of the twelve name pairs studied were brand–brand or brand–generic pairs converted to their generic names, which are far less similar to each other than the brand names were; and the study did not validate that the hospitals were using electronic prescribing, its only data source.

ISMP’s own conclusion is that the evidence is mixed largely because of methodological differences and study limitations, that gaps remain in understanding the role of tall man lettering in clinical settings, and that the technique is nonetheless worth implementing as one among numerous strategies. Its 2023 document notes ISMP’s participation in a four-year FDA-funded Northwestern University research project led by Bruce L. Lambert to assess the comparative effectiveness of different drug name text enhancements — the definitive study the 2016 editorial called for.

What that means for where you spend effort

A defensible reading for a medication-safety officer deciding on priorities:

Tall man lettering is cheap, low-risk and endorsed. There is no serious argument that it causes harm, and the configuration work is finite.
Its effect size in real clinical settings is unproven, so it does not justify displacing higher-yield controls — barcode-assisted medication administration, separating look-alike storage, indication-on-order, and independent double checks for genuinely high-alert products.
The marginal effort is best spent on consistency and on the surfaces closest to selection, not on expanding the name list. Getting the ADC screen and the pump library to match the pharmacy screen is worth more than adding twenty more pairs to a list that renders correctly in only half the estate.
Measure implementation, not outcome. The event rate for wrong-drug selection on a specific name pair is too low at a single institution to detect a change; per-surface rendering compliance is measurable this quarter.

Building the policy

A tall man lettering policy that will survive a survey and an EHR upgrade names six things:

The adopted source. The FDA Name Differentiation Project list, the ISMP list, or FDA plus a named subset of ISMP — with the version or retrieval date, since both are revised.
Local additions. Name pairs added from your own event data, with the CD3-derived form and the date and rationale for adding each one.
The surfaces in scope, listed individually, with the ones that cannot technically comply recorded as known gaps rather than omitted.
The verification schedule — per surface, and triggered by EHR upgrades, drug file content loads and ADC or pump library rebuilds, not only annually.
The communication plan. Given the evidence that awareness of purpose is part of the mechanism, “it appeared on the screen one Tuesday” is not an implementation.
The review cadence, tied to your P&T committee, with reported wrong-drug events feeding candidate additions.

When a look-alike/sound-alike selection error does reach a patient, the resulting review runs through the same machinery as any other adverse event: classification of the individual’s behaviour separately from the system’s contribution via a just culture algorithm, escalation criteria under sentinel event definitions where the harm threshold is met, and protection of the analysis itself under patient safety organization work-product privilege. A finding that tall man lettering was configured in pharmacy but not on the ADC screen is a system finding, and it belongs in the system column.

For the broader programme this sits inside, see the patient safety hub; practitioners formalising this work often pursue CPPS certification, and the same per-surface configuration discipline applies to other clinical decision support rollouts such as early warning score implementation.

What this page could not verify

In the interest of not passing along something unread: the FDA List of Established Drug Names Recommended to Use Tall Man Lettering was read in full directly from FDA’s Name Differentiation Project page, and the ISMP document FDA and ISMP Lists of Look-Alike Drug Names with Recommended Tall Man (Mixed Case) Letters was read in full, including both tables and its reference list. The broader ISMP List of Confused Drug Names — the full look-alike/sound-alike list, which includes many pairs that do not carry tall man letters — is distributed as a gated download requiring registration on ECRI’s ISMP resources site and has not been reproduced or summarised here. ISMP’s legacy ismp.org URLs now redirect to that ECRI-hosted site. Obtain the LASA list from ISMP directly; do not rely on a third-party copy, and do not treat any single reproduction of either list as current without checking the source date.

Frequently asked questions

Is tall man lettering required by The Joint Commission?

No. ISMP records it as recommended by The Joint Commission but not required, and states that tall man lettering was never required by any standards or regulatory agency. Look-alike/sound-alike medications are addressed as a risk category in accreditation expectations, but that is a different thing from a mandate to use this specific typographic convention.

Are the FDA list and the ISMP list the same?

No, and they should not be merged. FDA’s list comes from its Name Differentiation Project, covers established generic names only, and is the basis on which FDA asks manufacturers to voluntarily revise labels. ISMP’s published document reproduces the FDA list as Table 1 and then adds a considerably larger Table 2 of its own recommendations, which ISMP states is not an official FDA-approved list and is intended for voluntary use. ISMP’s additions include brand–brand and brand–generic pairs that FDA’s list does not cover.

How do you decide which letters to capitalise?

ISMP follows the CD3 rule where possible: working from the left, capitalise all characters to the right once two or more dissimilar letters are encountered; then, working back from the right, return two or more letters common to both names to lowercase; and where there are no common letters at the right-hand end, capitalise the central part of the name only. When that produces a poor result, an alternative is chosen. For any name already on the FDA or ISMP list, copy the published string rather than re-deriving it.

Does tall man lettering actually reduce medication errors?

The evidence is mixed and no definitive answer exists. Multiple laboratory studies between 2000 and 2021 found improved accuracy of drug name perception or reduced confusion. Other studies found no benefit — Schell in 2009 found no effect on recognition and an increase in false alarms, and Zhong and colleagues in 2016 found no significant reduction across 42 children’s hospitals over nine years, though that analysis could not confirm which hospitals had actually implemented the convention. A 2016 editorial in the same journal concluded the evidence was incomplete and conflicting and called for a definitive study; an FDA-funded multi-year comparative-effectiveness project is intended to answer it.

Which systems should display tall man lettering?

Every surface where a clinician reads a drug name: prescriber and pharmacy order-entry and selection screens, automated dispensing cabinet screens, computer-generated pharmacy labels, eMARs, standard order sets, smart infusion pump drug libraries, and shelf and bin labels. ISMP’s practitioner survey found adoption between 73% and 83% across these surfaces in 2016, with pump libraries and shelf labels lagging.

Why does tall man lettering sometimes not appear even though we configured it?

Common causes are a display field or print template that normalises case on render, a character limit that truncates the name before the capitalised block, an interface that rebuilds the display name from a source field instead of carrying the formatted string, or a drug information vendor content load that overwrote a local edit. ISMP’s survey specifically recorded respondents whose systems did not permit changing letter case, using mixed case, or bolding at all.

Can we invent tall man forms for name pairs that are not on either list?

Yes, and hospitals do add pairs from their own event data. Apply the CD3 rule deliberately, record each addition as a local decision with its rationale, and check that the result makes the two names look less alike rather than more. For any pair that is on the FDA or ISMP list, use the published form — ISMP asks that its and FDA’s schemes be followed specifically to promote consistency across institutions and vendors.

Primary sources

US Food and Drug Administration, FDA Name Differentiation Project — including the FDA List of Established Drug Names Recommended to Use Tall Man Lettering.
Institute for Safe Medication Practices, FDA and ISMP Lists of Look-Alike Drug Names with Recommended Tall Man (Mixed Case) Letters.
Institute for Safe Medication Practices, ISMP List of Confused Drug Names (the look-alike/sound-alike list), hosted by ECRI.
ISMP Medication Safety Alert! Acute Care, “Special edition: tall man lettering — ISMP updates its list of drug names with tall man letters,” 2 June 2016 — including the 2016 practitioner survey results.
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 — the source of the CD3 rule.
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. 2016;25(4):233-40.
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.