QT Prolongation: Risks, Medications, and What You Need to Know

When your heart’s electrical cycle takes too long to reset, it’s called QT prolongation, a delay in the heart’s repolarization phase that can trigger life-threatening irregular heartbeats. Also known as long QT syndrome, it’s not always genetic—many cases are caused by everyday medications, electrolyte imbalances, or a mix of both. This isn’t just a lab result—it’s a silent threat that can lead to torsades de pointes, a specific type of dangerous heart rhythm that can cause fainting, seizures, or sudden death if not caught early.

Some of the most common culprits are drugs you might not suspect. Antibiotics like ciprofloxacin, a fluoroquinolone used for urinary and respiratory infections, can disrupt heart rhythm even in healthy people. Antidepressants like sertraline, a widely prescribed SSRI for depression and anxiety, carry warnings for QT effects. Even anti-nausea drugs like ondansetron and certain antihistamines can push the QT interval past safe limits. It’s not about taking one drug—it’s often the combo. A painkiller here, an antibiotic there, low potassium from diuretics, and suddenly your heart’s timing is off.

Who’s most at risk? Older adults, women, people with kidney or liver problems, and those already on multiple medications. Low potassium, low magnesium, or low calcium—common from diet, vomiting, or diuretics—make QT prolongation much worse. It’s not rare. Studies show over 1 in 100 people on certain meds develop measurable QT changes. Most never know it until they collapse.

You won’t feel QT prolongation. No chest pain, no fluttering—just a quiet, dangerous delay. That’s why doctors check ECGs before starting risky drugs, especially if you’re on more than one. If you’ve ever passed out for no reason, or had unexplained dizziness, ask: could this be linked to what I’m taking?

Below, you’ll find real-world guides on how specific medications affect heart rhythm, how to spot hidden risks in your pill bottle, and what to ask your doctor before filling a new prescription. These aren’t theoretical warnings—they’re based on patient reports, FDA alerts, and clinical data. Know what’s in your medicine cabinet. Know what your heart is up against.