IStock Photo 3604938 © Denis Pepin

Take a moment to think of the names of any 5 prescription drugs. Your list may read something like: Viagra®, Nexium®, Vioxx®, Zyrtec®, and Lunesta®. Or, if pressed for another 5, maybe Yaz®, Xyzal®, Elidel®, Prozac®, and Paxil®. Notice anything unusual? Topomax®, Prevacid®, Oxycontin®, Celexa®, Botox®. Flomax®, Valtrex®, Zoloft®, Zantac®, Xanax®. How about now?

If you haven’t noticed—and in a New York Times interview, James L. Dettore, CEO of Miami’s Brand Institute, says you have—prescription drug brand names are awfully Z- and X-heavy. For some, the trend is bothersome; for others merely noticeable, just a faint registering on the consciousness. That registering, though, is the whole ballgame.

In an average string of English words—say, a letter, a newspaper article, a conversation, a novel—certain letters appear more often than others. Knowing the frequency at which a given letter will appear can be quite useful. When Samuel Morse invented his code, it is said he determined English letter frequency by counting the number of letters in printers’ type sets. He found that printers used E the most, followed by T, then A and O and I and N and S (all roughly the same amount), then H, and so on. Having an eye for economy, Morse gave E and T the shortest character sequences—a single dot and a single dash, respectively. He also found that the least common letters are J, X, and especially Z.

Other enterprises have depended, at least in part, on letter frequencies. The Linotype machine, once widely used for typesetting newsprint, has its keyboard arranged by frequency. Its first two letter columns, then, are ETAOIN SHRDLU, which nonsense phrase used to occasionally appear in error lines in newspapers. Code breaking also at one time or another has depended on letter frequency analysis: knowing the frequency of letters allows a simple substitution cipher—e.g. which substitutes B for A, C for B, D for C—to be broken rather quickly, since the character appearing most often is very likely to be E, the second-most to be T, and so on.

Today, letter frequency plays a powerful role in prescription drug brand names. The reason? Those rare letters—X’s and Z’s particularly—stand out like neon lights.

The letter X, for instance: people like saying words containing it, and the letter carries a host of associations with innovation and futurity. Think X-factor, Generation X, The X-Files, X-Box®, Xerox®. Likewise for the letter Z: its rarity is its strength as a marketing tool.

Below, the relative frequency—in documents of all sorts—of each letter of the alphabet is depicted in column 1. Column 2 is a letter-frequency analysis of the names of the top 200 drugs (by number of prescriptions dispensed):

In the first column, E appears most frequently, roughly 12.702% of the time; Z appears the least, only 0.074%, and X the second-least at 0.150%. This is the average, everyday frequency of these letters. In the second, pharmaceutical column, the letter Z appears over 13 times more, and the letter X almost 30 times more, than average. Instead of being the 2nd least frequent letter, X becomes the 12th most frequent. To put that in perspective, the letter X appears more often than B, D, F, G, H, J, K, M, Q, U, V, W, Y, or Z.

X- and Z-laden or not, brand names are technically meaningless—legally, they cannot describe (or even really imply) anything about what a drug does. But, according to Stanford Medicine Magazine, they are carefully “constructed to convey a sense of power or speed or tranquility without promising a cure.” Z and X can do a lot of the phonological heavy-lifting. According to Dettore, in an interview with the New York Times, X and Z not only look better but sound better: “The harder the tonality of the name, the more efficacious the product in the mind of the physician and the end user.”

Getting a drug name approved is an involved, lengthy process. Each drug has three names—a chemical (for, well, chemists), a generic (for doctors), and a brand (proprietary, for customers). So e.g.:

• 1-[4-ethoxy-3-(6,7-dihydro-1-methyl-7-oxo-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-5-yl)phenylsulfonyl]-4-methylpiperazine citrate

• = sildenafil citrate

• = Viagra®

The generic name must be approved by the US Adopted Names Council (whose generic naming guidelines are particularly comprehensive), and the brand name by both the FDA and the US Patent Office. The FDA winnows out brand names that could be misleading or confusable. It also sees that different forms of the same drug are differentiated: e.g., the same drug may be a racemic mixture (i.e. containing equal amounts of the drug molecule and its mirror-image) or enantiopure (i.e. one molecular formation only, no mirror-images allowed). Though technically the same drug, these two forms must receive different names, since their effects and side-effects may differ. The necessity of differentiation swells the need for exotic names.

Many brand names, sometimes a dozen or more, get tested before a pharmaceutical company chooses the most effective; on average, somewhere between $500,000 and $2.5 million are spent developing a new brand name. Why? A drug’s brand name can have an enormous impact on its popularity. (Remember, the names above are the 200 drugs with the most prescriptions dispensed.) A “Viagra®” can sell like hotcakes while, say, a “Revatio®” (which is the exact same drug) remains relatively obscure.

So when a drug name sounds suspiciously like a sci-fi movie title, remember: it’s meant to sound that way.