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Last reviewed and revised February 27, 2013

Writing a Prescription
Must It Be This Way?
Conclusion

Somehow, I never thought to question the assumption that knowing Latin would help me understand medical terms I would need to learn in medical school. So when I got to college, I abandoned the Spanish I'd taken for two years in high school and signed up for Latin.

In fact, while many medical terms have their roots in Greek or Latin, I'd have been much better off continuing with Spanish or learning Russian, since the hospital where I trained and continue to work attracts a large number of people who speak those languages. But there I was, trying to memorize a language I would never actually speak so that I could be readily fluent by the time I got to medical school — a misguided approach to say the least! You don't need to go to such lengths — read on to learn some of the Latin terms doctors use every day when writing prescriptions.

Writing a Prescription

Never mind the handwriting; even if you could read it, the terms that appear on most prescriptions are probably incomprehensible. A tradition has developed about how to specify the dose of a medication, whether to take it by mouth or in some other way, how often it should be taken, and other details. In a way, it's like writing a check — certain information goes in certain places in a format that is unlike your usual way of writing. Here's what a prescription looks like. To decipher it, see the numbers below that link to the labels on the prescription.

To understand the entries for each of these, some translation and explanation are necessary:

The patient's name should be easy to read. To better identify the patient for whom the prescription is intended, the patient's date of birth and/or address is sometimes included. Many doctors and hospitals are using typed or computer-generated prescriptions that eliminate hand-written information (except for the doctor's signature);

For most medications, the date of the prescription must be within a year of today's date. However, for certain medications, such as narcotics, the prescription may need to be much closer to the present date (for example, within 30 days).

Name of the medication. To avoid names that sound alike, the generic name may appear here rather than the brand name you know. Because many medications sound alike and are spelled alike, care must be taken to make this important information clear. If a generic version or a brand name is preferred by the ordering physician, the words "no substitution" or "brand name medically necessary" may appear near the medication's name. Some prescriptions offer a choice where the physician signs, one for generic and another for brand name.

The dosage might be in milligrams (mg), micrograms (mcg), grams (g) or other unit of measure.

The number of doses (pills, injections, and so on) to be taken at one time, denoted as "i, ii, iii or iiii" for 1, 2, 3 or 4; often the term "sig" will appear just in front of these (short for the Latin, signetur, or "let it be labeled").

The mode of administration:
- po — from the Latin per os, or "by mouth" or "orally"
- pr — from the Latin per rectum, or "by way of the rectum," meaning by suppository
- sl — sublingual (under the tongue)
- IV — intravenous (into the vein)
- IM — intramuscular (in the muscle)
- SQ — short for subcutaneous (meaning under the skin)

The frequency of administration:
- qd — every day, from the Latin quaque die,
- bid — twice a day, from the Latin bis in die
- tid — three times a day, from the Latin ter in die
- qid — means four times a day, from the Latin quater in die
If the medication is to be taken in a particular way — for example, at night or after food — that comes next:
- pc — after meals or not on an empty stomach, from the Latin post cibum
- qhs — each night, from the Latin quaque hora somni, or "at bedtime"
- prn — as needed, from the Latin pro re nata, "as circumstances may require"

A number sign and the number of doses for the entire prescription follow. If it is a one-month supply of a medicine taken three times each day, it will read "#90"; sometimes doctors use "Disp" as shorthand for "dispense," instructing the pharmacist to provide that number of doses.

The number of refills allowed is next. For example, it might say "3RF" for three refills. Some prescription pads have a box for the number of doses and number of refills to be entered directly.

For some prescriptions, but not all, additional information is required, including doctor's Drug Enforcement Agency (DEA) number. For example, certain controlled substances, including narcotics, require a valid DEA number.

Finally, the doctor's name, printed and signed, complete the prescription.

Must It Be This Way?

Perhaps prescriptions are written this way because it carries on a tradition that organizes information in a standard way that pharmacists and other health care professionals will understand. But there are so many ways for it to go wrong (and so often it does go wrong) that the case could be made to require plain language instead of abbreviated Latin on medication orders.

It's easy to see how "Celexa" and "Celebrex", two drugs that were approved around the same time, could be mistaken if written or read quickly; how "i tid" could be mistaken for "i bid"; or how "i qid" and "i qd" could be confused. Computer programs that "translate" into more understandable language and a requirement that all information is printed using both brand and generic drug names are other suggestions that might make the prescriptions you get from your doctor easier to understand.

Conclusion

Using our hospital's computer system, when I type "ii po qid", the prescription reads "2 by mouth 4 times daily." As time goes by, I'm amazed not only by how helpful a computerized prescription-entry system is but how unnecessary my struggles in Latin class were. The advantages to a computer-assisted prescription system go well beyond making the writing legible.

Now you know why the prescription you take to the pharmacist often reads like gibberish. Fortunately, the pharmacist is in on the "code" doctors use when they write prescriptions — and now you are, too.

Robert H. Shmerling, M.D., is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.

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