Dangerous Medical Abbreviations That Still Cause Deadly Errors

Every year in the U.S., hundreds of patients are harmed - some fatally - because a doctor wrote QD instead of daily, or MS when they meant morphine sulfate, not magnesium sulfate. These aren’t hypothetical risks. They’re real, documented mistakes that happen in hospitals, clinics, and pharmacies every single day. And the worst part? We’ve known how to stop them for over 20 years.

What You’re Really Writing When You Use ‘QD’

The most dangerous abbreviation in all of medicine isn’t some obscure code. It’s QD. Doctors use it to mean “once daily.” But here’s what actually happens: nurses, pharmacists, and even other doctors see it and think “QID” - four times a day. Or worse, they misread it as “QOD” - every other day. A 2018 analysis of nearly 5,000 medication errors found that QD alone caused 43.1% of all abbreviation-related mistakes. That’s more than half of all errors tied to shorthand.

Imagine a patient with high blood pressure. The doctor writes “Lisinopril 10 mg QD.” The pharmacist sees it as “QID” and dispenses four times the dose. The patient ends up in the ER with dangerously low blood pressure. This isn’t fiction. It’s happened. And it’s still happening.

Why ‘MS’ Can Kill

Another deadly mix-up involves MS or MSO4. To many, it’s clearly morphine sulfate - a powerful painkiller. But to others, especially in high-stress environments, it looks like MgSO4 - magnesium sulfate, used for seizures or preeclampsia. These drugs are completely different. One calms pain. The other stops seizures. Give the wrong one, and you could kill someone.

According to the NCBI’s StatPearls review, MS is the most common drug abbreviation error in the U.S. A 2022 Reddit thread from pharmacists showed 87% of respondents had intercepted a similar error. One pharmacist described catching “MS 10 mg SC” on a chart - and realizing the patient was supposed to get morphine, not magnesium. If the nurse had drawn it up without double-checking? The patient could’ve gone into cardiac arrest.

The ‘U’ That Looks Like a Zero

Then there’s U - short for “unit.” Sounds simple, right? But in handwriting, it looks exactly like a zero (0) or the number four (4). And in some cases, it’s mistaken for “cc” (cubic centimeters). This isn’t just a typo. It’s a life-or-death mix-up.

ISMP’s data shows that U is the second most common error after QD. A diabetic patient was once given 100 units of insulin - written as “100U.” The nurse read it as “1000.” The patient’s blood sugar crashed. She nearly died. Another case: a patient was supposed to get 5 units of heparin. The order said “5U.” The nurse saw “50” and gave ten times the dose. Both incidents were reported in the ISMP National Medication Errors Reporting Program.

Even worse? The abbreviation IU (international unit) is often confused with IV (intravenous) or even “10.” That’s how a patient ended up with an IV drip of a drug meant to be taken orally. The confusion? IU looked like IV on a blurry fax.

Why ‘SC’ and ‘SQ’ Are Both Trouble

Route of administration matters. If a drug is meant to go under the skin (subcutaneous), giving it into a vein (intravenous) can cause sudden, severe reactions.

Two abbreviations for subcutaneous - SC and SQ - are both banned. Why? Because SC can be mistaken for SL (sublingual), and SQ looks like “5 every” when handwritten. One pharmacist in Wisconsin intercepted a prescription for “Insulin SQ” that was read as “Insulin 5 every.” The patient was given five doses at once. Their blood sugar dropped so fast, they needed emergency glucose.

Other Hidden Traps

There’s BIW - meant to mean “twice weekly.” But in practice, it’s often read as “twice daily.” A 2019 report in Pharmacy Times detailed how a patient on chlorambucil (a chemotherapy drug) got the wrong dose because of this. The error led to bone marrow suppression and a months-long hospital stay.

NMT was supposed to mean “nebulizer mist treatment.” But one nurse thought it meant “no more than.” The patient was given a much smaller dose of hypertonic saline - and didn’t get the lung treatment they needed.

Drug names are even worse. AZT (zidovudine) gets confused with azathioprine or aztreonam. TAC (triamcinolone cream) looks like Tazorac - two different skin treatments. One patient got the wrong cream, and their rash got worse. Handwriting made it worse. A 2017 case study showed the error happened because the doctor’s “TAC” looked like “Tazorac” on a faded copy.

What’s the Solution?

The fix isn’t complicated. It’s been known since 2001. The Joint Commission and the Institute for Safe Medication Practices (ISMP) created a simple list: Do Not Use. No more QD. No more U. No more MS. No more SC or SQ.

Instead, write it out:

• Write “daily,” not “QD”
• Write “units,” not “U”
• Write “morphine sulfate,” not “MS”
• Write “subcutaneous,” not “SC” or “SQ”
• Write “twice weekly,” not “BIW”

It’s not harder. It’s just different. And it saves lives.

Why Do People Still Use Them?

You’d think after 20+ years, everyone would’ve switched. But they haven’t.

A 2022 survey by the American Medical Association found that 43.7% of doctors over 50 still use banned abbreviations. Why? Habit. Tradition. “I’ve been doing it this way for 30 years.” But that’s not a reason - it’s a risk.

Electronic health records (EHRs) helped. A 2021 study showed they cut abbreviation errors by 68%. But they didn’t fix everything. Nearly 13% of errors in EHR systems still came from free-text fields where someone typed “QD” or “MS” anyway.

The real problem? Culture. Not technology. As Dr. Lucian Leape from Harvard said in 2023: “The persistence of dangerous abbreviations represents a failure of professional culture.” We know the right way. We just haven’t made it mandatory enough.

What’s Changing Now?

In January 2024, ISMP added 17 new banned abbreviations - mostly around HIV medications like DOR, TAF, and TDF. Why? Between 2019 and 2023, errors with these terms jumped 227%. They’re new drugs. But the same old mistakes are happening.

Some EHR systems now auto-correct. Epic Systems rolled out AI tools in 2023 that flag “QD” and replace it with “daily” before the order is sent. By 2026, 85% of major systems will do this automatically - even for voice dictation.

But until then? The responsibility falls on you.

What You Need to Do Today

If you’re a prescriber:

• Stop using QD, U, MS, SC, SQ, BIW, IU, NMT, AZT, TAC, and any other shorthand.
• Write everything out. Full names. Full instructions.
• Double-check your orders before hitting “send.”

If you’re a pharmacist or nurse:

• Always question unclear orders. Don’t assume.
• Call the prescriber. Say: “I need to clarify - is this ‘daily’ or ‘every other day’?”
• Use the ISMP ‘Do Not Use’ list as your checklist.

It’s not about being rigid. It’s about being clear. One extra second writing out “daily” instead of “QD” could mean the difference between life and death.

How Bad Is This Really?

The numbers don’t lie:

• 37% of all medication errors could be prevented by eliminating these abbreviations.
• 150,000 adverse drug events happen every year because of them.
• $1.27 billion in annual costs are tied to these mistakes.
• Facilities that fully enforce the rules cut errors by 89.4% in 18 months.

And yet - we still have doctors writing “MS” on paper charts. We still have pharmacists guessing what “U” means. We still have nurses giving the wrong dose because they misread a letter.

This isn’t a technical problem. It’s a human one. And it’s fixable - right now.