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 medications, electrolyte problems, or other health conditions. This isn’t just a lab result; it’s a red flag that could lead to torsades de pointes, a specific type of dangerous heart rhythm that can cause fainting, seizures, or sudden death if not caught early.

Many common drugs can cause QT prolongation, including some antibiotics, antidepressants, antifungals, and even over-the-counter antihistamines. For example, certain versions of acyclovir, an antiviral used for herpes infections, have been linked to this issue. So have drugs like citalopram, a widely prescribed antidepressant, and fluconazole, a common antifungal. It’s not just about the drug itself—low potassium, low magnesium, or kidney problems can make the risk much worse. That’s why doctors check your electrolytes and kidney function before prescribing some of these meds.

People with heart disease, older adults, and those taking multiple medications at once are at higher risk. It’s not something you can feel directly, but if you’ve had unexplained fainting, dizziness, or a racing heartbeat after starting a new drug, it’s worth asking your doctor about an ECG. The good news? Stopping the trigger, correcting electrolytes, or switching meds often fixes it fast. You won’t find QT prolongation listed as a side effect on every pill bottle, but it’s one of the most serious ones doctors monitor closely.

Below, you’ll find real-world guides on medications that can affect your heart rhythm, how to spot hidden risks, and what to ask your provider when a new prescription comes your way. These aren’t theoretical discussions—they’re practical checks you can use to protect your heart.