Physicians write billions of prescriptions every year. How many different kinds of drugs are there? How many drugs does the average patient take?  What’s the difference between brand name drugs, generic drugs, and active ingredients? What’s the best way to represent medications in a computational model? I will answer these questions and more in this brief introduction to pharmacology.

How many drugs are there?

According to DrugBank, there are nearly 12,000 different drugs in existence, including:

  • >3,700 approved drugs
  • >5,700 experimental drugs
  • > 200 illicit drugs (I have to admit, I was surprised by how big this number is…TWO HUNDRED?)

How many drugs does the average patient take?

The Centers for Disease Control and Prevention (CDC) reports the following:

  • 49% of people have used at least 1 prescription drug in the past month
  • 23% of people have used 3 or more prescription drugs in the past month
  • 12% of people have used 5 or more prescription drugs in the past month

In 2015, physicians prescribed 3.7 billion drugs at outpatient visits in the United States. The most frequent classes of drugs prescribed were analgesics (painkillers), antihyperlipidemic agents (e.g. drugs to lower cholesterol), and antidepressants.

The elderly take over a third of all prescription drugs. On average, an elderly person takes more than 5 prescription medications if they live independently, and 7 if they live in a nursing home.


Stothert castor oil pills

Drug Naming Example

Here’s one example of several names for the same drug:

  • Chemical name: N-(4-Hydroxyphenyl)acetamide
  • Generic name/active ingredient: acetaminophen
  • Brand name: Tylenol (company: McNeil Consumer Healthcare)
  • Also sold as a generic drug under various generic brand names such as Panadol (company: GlaxoSmithKline)


Tylenol bottle

I’m pretty convinced that this drug naming system was designed solely to torture medical students, who feel like they’re learning a foreign language memorizing alien-sounding ingredients, brand names, and generic names that all refer to the same medicine at the end of the day. But, like it or not, the drug naming “system” is here to stay.

How Drug Naming Works: A Timeline

In the beginning…the drug is discovered. In the end, someone uses the drug. Along the way the drug earns many names. Here are the details, with another running example for the drug azithromycin:

  1. Discovery of the drug: at this point the drug is referred to by its chemical name, which describes the molecular structure. Example: (2R,3S,4R,5R,8R,10R,11R,12S,13S,14R)-13-[(2,6-dideoxy-3-C-methyl-3-O-methyl-α-L-ribo-hexopyranosyl)oxy]-2-ethyl-3,4,10-trihydroxy-3,5,6,8,10,12,14-heptamethyl-11-[[3,4,6-trideoxy-3-(dimethylamino)-β-D-xylo-hexopyranosyl]oxy]-1-oxa-6-azacyclopentadecan-15-one
  2. Early studies of the drug: because people don’t like saying the aforementioned chemical name out loud (say it five times fast), they may come up with an abbreviated name to refer to the drug easily in early studies. This is typically a short sequence of letters and numbers.
  3. Huge Pharmaceutical Company carries out all the human and animal studies needed for FDA approval. When the drug is finally approved by the FDA, the drug receives two names:
    1. Brand name: Huge Pharmaceutical Company owns this name. e.g. Sumamed (company: Pliva).
    2. Generic name: This is intended as a general-purpose name to describe the active ingredient in the brand name drug, e.g. azithromycin is the generic name for the branded drug Sumamed
  4. After Huge Pharmaceutical Company’s patent and marketing exclusivities expire, Other Drug Company can start selling the drug after a quick FDA approval process that is much easier than the original approval process. Other Drug Company can either sell the drug under the generic name (e.g. “azithromycin”) or they can come up with their own brand name that is different from the original brand name. e.g. Zithromax (company: Pfizer).


Azithromycin tablets

So a single medicine has a chemical name, an abbreviated name, an original brand name, a generic name, and possibly numerous “generic brand names” (which are a brand names created by a company selling a generic version of the drug.) Yay!

(Side note about where the names come from: Some generic names are a shortened version of the drug’s chemical name or chemical formula. Brand names are often designed cleverly to convey something about the drug’s function, e.g. Skelaxin relaxes skeletal muscles, Lopressor lowers blood pressure, and Glucotrol controls blood glucose levels.)

Section Reference: Overview of Generic Drugs and Drug Naming

Why Generic Drugs Cost Less

Generic drugs are typically 85% less expensive than the brand-name versions for a few reasons:

  1. Other Drug Company that wants to sell the generic drug doesn’t have to carry out the expensive human and animal trials required by the FDA for Huge Pharmaceutical Company’s initial drug approval. Since the drug has already been approved, Other Drug Company only has to fill out  an “abbreviated new drug application” which does not require expensive experiments.
  2. Multiple companies often get FDA approved to make the same generic drug, and competition between these companies lowers the price for consumers.

The IMS Health Institute estimates that use of generic drugs saved the United States $1.67 trillion between 2007 and 2016.

Do generic drugs work?

Generic drugs must meet rigorous equivalency standards in order to be approved – i.e., if you’re selling “acetaminophen” the FDA makes sure that you’re actually selling “acetaminophen” and not snake oil. Quoting the FDA,

A generic drug is a medication created to be the same as an already marketed brand-name drug in dosage form, safety, strength, route of administration, quality, performance characteristics, and intended use.

For details about the standards that generic medicines must meet in order to receive FDA approval, you can read the section reference, FDA Generic Drugs Questions and Answers, or check out this page, What is the Approval Process for Generic Drugs?


Snake oili.e. NOT what we find in an acetaminophen bottle (thank you, FDA!)

More Naming Examples

In the tables below, I’ve grouped all of the brand names into one column, including the original brand name and any brand names created by companies selling generics of the drug. I’ve also listed the “true generic name” (i.e. the generic name that was created when the drug was first FDA approved) under “Generic Names/Active Ingredients”:


This chart reiterates that there are multiple brand names for the same active ingredient, and there can also be multiple brand names for drugs containing multiple active ingredients.  “Excedrin PM Headache” includes three active ingredients: acetaminophen (sold alone under the brand name Tylenol), aspirin (sold alone under the brand name Ascriptin), and diphenhydramine (sold alone under the brand name Benadryl.)

Sometimes, companies go a little insane with the brand names:


Here’s another table, this one adapted from Wikipedia, showing some chemical names, generic names/active ingredients, and example brand names:


How to represent drugs in a model

What are we going to do with this mess? In the electronic health record, any of the brand names or generic names could be used to describe the same medication. But we don’t want to have fifty different inputs to our model that all mean “warfarin” at the end of the day.

Thus, the simplest solution to ensuring that you feed your model nice clean data is to pre-process all of the drug names into active ingredients ONLY. That means every single brand name for warfarin gets transformed into “warfarin” and we leave it at that. Every time “Excedrin PM Headache” is mentioned, we transform it into “acetaminophen, aspirin, diphenhydramine.” To implement this in code, you need a table that lists what active ingredient(s) correspond to each brand name.

Featured Image: Various Pills


I hope you enjoyed this introduction to pharmacology! Future pharmacology posts will include more information about different categories of drugs and what diseases they can treat.