Why some letters in a medicine name are capitals

predniSONE, hydrOXYzine and buPROPion are ordinary names (prednisone, hydroxyzine, bupropion) written in Tall Man lettering: the capitals mark the letters that differ from a look-alike name, such as prednisoLONE, hydrALAZINE or busPIRone. The capitals are not part of the name. The US FDA keeps a list of 21 such sets; every one is below. Type a name, in any capitals, to find its set.

Try:

21 sets and 2 names listed on their own

FDA's Tall Man list

Each row is one set of look-alike names as FDA's table gives it, in FDA's order: the Tall Man spelling, then the ordinary lower-case name, which opens it in the decoder. methylPREDNISolone and methylTESTOSTERone are in two rows, as FDA lists them. The list below has 43 different spellings over FDA's 23 rows, from the FDA page as the Internet Archive saved it on 2026-09-18.

Look-alike names	FDA row
acetoHEXAMIDE acetohexamide acetaZOLAMIDE acetazolamide	row 1
buPROPion bupropion busPIRone buspirone	row 2
chlorproMAZINE chlorpromazine chlorproPAMIDE chlorpropamide	row 3
CISplatin cisplatin CARBOplatin carboplatin	row 4
clomiPHENE clomiphene clomiPRAMINE clomipramine	row 5
cycloSPORINE cyclosporine cycloSERINE cycloserine	row 6
DAUNOrubicin daunorubicin DOXOrubicin doxorubicin	row 7
dimenhyDRINATE dimenhydrinate diphenhydrAMINE diphenhydramine	row 8
DOBUTamine dobutamine DOPamine dopamine	row 9
glipiZIDE glipizide glyBURIDE glyburide	row 10
hydrALAZINE hydralazine hydrOXYzine hydroxyzine	row 11
medroxyPROGESTERone medroxyprogesterone methylPREDNISolone methylprednisolone methylTESTOSTERone methyltestosterone	row 13
methylPREDNISolone methylprednisolone methylTESTOSTERone methyltestosterone	row 14
migALAstat migalastat migLUstat miglustat	row 15
niCARdipine nicardipine NIFEdipine nifedipine	row 17
predniSONE prednisone prednisoLONE prednisolone	row 18
risperiDONE risperidone rOPINIRole ropinirole	row 19
sulfADIAZINE sulfadiazine sulfiSOXAZOLE sulfisoxazole	row 20
TOLAZamide tolazamide TOLBUTamide tolbutamide	row 21
traZODone trazodone traMADol tramadol	row 22
vinBLAStine vinblastine vinCRIStine vincristine	row 23

Listed on their own

FDA's table has 2 rows with a single name and no look-alike partner named beside it. The table does not say which name each is confused with, so this page does not either.

Name	FDA row
HYDROmorphone hydromorphone	row 12
mitoXANTRONE mitoxantrone	row 16

What the capitals mean, in FDA's words

Tall man lettering (TML) is a technique that uses uppercase lettering to help differentiate look-alike drug names. Starting on the left side of a drug name, TML highlights the differences between similar drug names by capitalizing dissimilar letters (e.g., vinBLAStine versus vinCRIStine and CISplatin versus CARBOplatin). TML can be used along with color or bolding to draw attention to the dissimilarities between look-alike drug names, and alert healthcare providers that the drug name can be confused with another drug name.
In 2001, FDA initiated the name differentiation project to continually evaluate postmarketing reports of name pair confusion, and determine if TML should be used to help differentiate similar established names. […] If FDA’s evaluation determines TML is an appropriate approach to address reports of name confusion, FDA will request the manufacturer voluntarily revise their labels and labeling to use TML, and then update the FDA List of Established Drug Names Recommended to Use Tall Man Lettering.

US Food and Drug Administration, FDA Name Differentiation Project (a US government work, quoted as written; FDA's footnote marker left out)

So the capitals are a way of writing a name, not a different name. The official names stay lower case: WHO's International Nonproprietary Name, the US adopted name and the name in FDA's own drug databases are prednisone, not predniSONE. When you look a name up, here or anywhere, the capitals can be ignored; this site's decoder and the box above treat predniSONE, PREDNISONE and prednisone as the same name.

FDA's list covers established names, the generic names on US labels. Brand names are not on it. Because FDA asks manufacturers to change their labels voluntarily, the same name can be printed in capitals on one pack and in plain letters on another.

Reading a pair: which letters get the capitals

FDA describes the method as working from the left of the name and capitalising the letters that are not alike. In practice the capitals pick out the syllables that make each name recognisable, and the list does not follow a strict letter-by-letter rule:

predniSONE / prednisoLONE. The two names share their first eight letters, predniso; the first difference is the ninth letter (n against l). FDA still capitalises SONE, starting two letters earlier, so that each name ends in a capitalised word-like chunk: SONE against LONE.
hydrOXYzine / hydrALAZINE. Both names are 11 letters, start hydr and end zine. FDA capitalises only OXY in one, but all of ALAZINE in the other, ending included.
buPROPion / busPIRone. The names part after bu. The capitals cover PROP and PIR; the endings ion and one also differ but stay lower case.
DOBUTamine / DOPamine and CISplatin / CARBOplatin. These names part within their first three letters, so the capitals start at the very beginning, the shared DO and C included; the shared endings amine and platin stay lower case.
rOPINIRole / risperiDONE. The pair shares only its first letter, r. The capitals are in the middle of one name and at the end of the other.

So read the capitals as "this is the part to check", not as a syllable break or a pronunciation guide. They say nothing about the medicine itself.

ISMP's longer list

The Institute for Safe Medication Practices (ISMP), a US non-profit, publishes a separate and much longer list, Look-Alike Drug Names with Recommended Tall Man (Mixed Case) Letters, on the site of ECRI, the organisation ISMP is now part of. FDA's own page cites ISMP for the technique. ISMP's list includes brand names and many generic pairs that are not on FDA's list. It is copyrighted, so this site links to it and does not copy it: if your name is not in the table above, look there.

What is not here

Other lists. Only FDA's list is reproduced. ISMP's list is linked, not copied, and national lists from other countries are not included, so a pair written in capitals on a label outside the US may be missing. Newer changes. The table is FDA's page as saved on the snapshot date above; if FDA has changed the list since, the change is not here until the page is rebuilt. Anything about the medicines. The list says two names look alike on paper or a screen; this page does not say what either medicine is or does.

Source

FDA Name Differentiation Project: FDA List of Established Drug Names Recommended to Use Tall Man Lettering (TML), US Food and Drug Administration. fda.gov turns away automated downloads, so the table was read from the Internet Archive snapshot of 2026-09-18, downloaded 2026-09-25. FDA text is a US government work.

The whole list is one file, tall-man.json, with the FDA address, the archive address, the snapshot time and the download date.