Dangerous Medical Abbreviations That Cause Prescription Errors and How to Avoid Them

One wrong letter on a prescription can kill. It’s not a scare tactic-it’s fact. In 2022, over 1,500 preventable deaths in U.S. hospitals were linked to misread medical abbreviations. These aren’t typos. They’re deeply rooted habits that still slip through, even in high-tech hospitals. And the worst part? Most of them are avoidable.

Why These Abbreviations Are So Dangerous

Here’s what happens when these abbreviations stay in use:

• A nurse gives insulin because ‘U’ was misread as ‘4’-leading to a fatal overdose.
• A pharmacist dispenses morphine instead of magnesium sulfate because ‘MS’ and ‘MgSO4’ looked too similar.
• A patient gets chlorambucil twice daily instead of twice weekly because ‘BIW’ was mistaken for ‘BID’.

These aren’t rare. In a 2022 survey of 1,843 pharmacists, 63.7% said they’d intercepted at least one dangerous abbreviation error in the past year. The top three? ‘QD,’ ‘U,’ and ‘MS.’

The Top 5 Dangerous Abbreviations You Must Stop Using

These five are the most common culprits-and they’re banned in every accredited U.S. hospital.

1. QD - This stands for ‘quaque die’ (once daily). But it looks like ‘QID’ (four times daily) or ‘QOD’ (every other day). A 2018 analysis of nearly 5,000 medication errors found that QD caused 43.1% of all abbreviation-related mistakes. Solution? Write ‘once daily’ in full.
2. U - Stands for ‘unit.’ But handwritten, it looks like a ‘0,’ a ‘4,’ or even a ‘cc.’ In one case, a patient received 100 units of insulin because ‘10U’ was read as ‘100.’ Solution? Always write ‘units’ in full.
3. MS or MSO4 - Means morphine sulfate. But it’s almost identical to ‘MgSO4’ (magnesium sulfate). Mixing them up can cause respiratory arrest or cardiac arrest. Morphine depresses breathing. Magnesium can stop your heart. Solution? Always write ‘morphine sulfate’ or ‘magnesium sulfate’ in full.
4. SC or SQ - Both mean subcutaneous. But ‘SQ’ can be misread as ‘5 every’ (especially in messy handwriting). ‘SC’ has been confused with ‘SL’ (sublingual), leading to wrong drug routes. Solution? Use ‘subcutaneous’ or ‘SubQ’ (if allowed by your facility).
5. cc - Cubic centimeters. Sounds harmless, right? But it’s often mistaken for ‘U’ (units). A 2020 study found that 1 in 4 insulin errors involved ‘cc’ and ‘U’ confusion. Solution? Always use ‘mL’ (milliliters).

Other High-Risk Abbreviations You Might Not Know

Some abbreviations are less common but just as deadly:

• TIW or BIW - ‘Twice a week’ or ‘twice a week.’ Often read as ‘twice daily.’ A patient on chlorambucil nearly died when this happened.
• IU - International Unit. Looks like ‘IV’ (intravenous) or ‘10.’ In one case, a patient got an IV dose of vitamin D because ‘10 IU’ was read as ‘10 IV.’
• AZT - Zidovudine. Mistaken for azathioprine (an immune suppressant) or aztreonam (an antibiotic). Wrong drug, wrong outcome.
• TAC - Triamcinolone cream. Looked like ‘Tazorac’ (a different acne medication) due to sloppy handwriting. Patient got the wrong skin treatment.
• NMT - Nebulizer mist treatment. Interpreted as ‘no more than.’ Patient received a higher dose of hypertonic saline than intended.
• DTO - Diluted tincture of opium. Confused with morphine sulfate. Led to dangerous opioid overdose.

These aren’t just ‘bad handwriting’ issues. They’re systemic failures. Even in digital systems, free-text fields still let these slip through.

How Hospitals Are Fighting Back

Some places have turned the tide. Mayo Clinic cut abbreviation-related errors by 92.3% in just two years. How? Three things:

1. EHR hard stops - If you type ‘QD,’ the system won’t let you submit. It forces you to write ‘once daily.’
2. Real-time alerts - Pharmacists get instant notifications when dangerous abbreviations appear in e-prescriptions.
3. Education with consequences - Every prescriber gets mandatory training. Repeat offenders get flagged.

It works. A 2021 study showed that facilities using hard stops reduced errors by 84.6%. Those relying only on education? Only 52.3% improvement.

But not everyone is on board. A 2022 AMA survey found that 43.7% of physicians over 50 still use banned abbreviations. They say, ‘I’ve always written it this way.’ But safety isn’t about tradition. It’s about survival.

What You Can Do-Even If You’re Not a Doctor

You don’t need to be a pharmacist to protect yourself or a loved one. Here’s how:

• Ask - When you get a prescription, ask: ‘Can you write that out in full?’ If you see ‘MS,’ ‘U,’ or ‘QD,’ say: ‘Can you spell that out?’
• Check - Compare the label on your pill bottle to the doctor’s note. If it says ‘morphine sulfate’ but the script says ‘MS,’ ask why.
• Report - If you spot a dangerous abbreviation on a prescription, tell the pharmacist. They’re trained to catch this. You’re their eyes.

One woman in Ohio saved her husband’s life when she noticed ‘U’ on his insulin script. She called the pharmacy. The pharmacist realized the dose was 10 times too high. She didn’t have a medical degree. She just knew to question it.

What’s Changing in 2026?

The fight isn’t over. In January 2024, ISMP added 17 new abbreviations to their watch list-mostly for HIV medications like DOR, TAF, and TDF. Why? Errors involving these jumped 227% from 2019 to 2023.

AI is stepping in. Epic Systems now has tools that auto-detect dangerous abbreviations in real time. By 2026, most voice-to-text systems will automatically correct ‘QD’ to ‘once daily’ as you speak.

But technology alone won’t fix this. Culture will. Until every prescriber, nurse, and pharmacist treats abbreviations like loaded guns-until they’re banned, not tolerated-we’re still risking lives.

Bottom Line

There’s no excuse for using ‘QD,’ ‘U,’ ‘MS,’ or any other dangerous abbreviation in 2026. We’ve known what to do for over 20 years. We’ve got the tools. We’ve got the data. What’s missing is consistency.

Every time you write ‘once daily’ instead of ‘QD,’ you’re not just following rules. You’re saving a life. And that’s not just good practice. It’s your responsibility.