Trazodone and QTc: the QT drug you prescribe every night — and never count
Cardiac Safety · Clinical Blind Spots
Trazodone and QTc: the QT drug you prescribe every night — and never count
The Quick Take
- CredibleMeds files trazodone as only a “conditional” QT risk — so it rarely makes your mental list of QT drugs. Its FDA label is sharper: avoid in known QT prolongation, with torsades reported at doses of 100 mg or less.
- Because it’s written for sleep, it’s the contributor you forget to tally — even while you’re carefully counting the patient’s other agents.
- The effect is concentration-dependent: stacking (methadone, ondansetron, antipsychotics), CYP3A4 inhibitors that raise trazodone levels, advanced age, and low K⁺/Mg²⁺ all amplify it.
- The fix isn’t to abandon trazodone. It’s to count it.
Here’s a scene from any busy week. Your patient is on citalopram, with an ondansetron you reach for when the nausea flares. Sleep is the holdout, so you add — almost reflexively — “just 50 mg of trazodone at bedtime.” You ran the QT math before you wrote the citalopram. You did not run it again for the trazodone, because in your head trazodone isn’t a QT drug. It’s a sleep aid.
That reflex is the blind spot. Trazodone is one of the most widely prescribed off-label hypnotics in psychiatry, and it almost never appears on the mental tally a clinician keeps for QT-prolonging agents. The pharmacology disagrees.
Why trazodone touches the QT at all
Like nearly every drug that prolongs the QT interval, trazodone blocks the rapid delayed-rectifier potassium current (IKr, the hERG channel), the current that drives the heart’s electrical reset after each beat. Slow that reset and the QT interval lengthens. Crucially, the effect tracks blood level — so a higher dose, a failing liver, or a CYP3A4 inhibitor that raises the trazodone concentration raises the QT effect along with it. That is the additive, concentration-driven logic behind every QT decision, applied to a drug most clinicians have mentally filed under “harmless.”
The classification gap that hides the risk
This is where trazodone slips through. CredibleMeds — the reference most clinicians lean on — places trazodone in the conditional risk category: a drug that prolongs QT or provokes torsades only under certain conditions, such as excessive dose, an interacting drug, or a predisposed patient. “Conditional” reads as reassuring, and the eye moves on.
The FDA label tells a less comfortable story. It warns explicitly against trazodone in patients with known QT prolongation, and torsades de pointes has been reported at doses of 100 mg or less — squarely inside the range you’d use for sleep. The gap between the reassuring category and the cautionary label is exactly the space the drug hides in. “Conditional” on paper does not mean “inconsequential” in a patient who already carries QT risk.
When the sleeper wakes up
Trazodone rarely prolongs the QT on its own in a structurally normal heart. It becomes dangerous when it stacks — which, given how it’s prescribed, is often. Watch for it when:
The amplifiers
- It’s stacked on other QT drugs — methadone, ondansetron, an antipsychotic, a fluoroquinolone or azole. Each is additive; trazodone is the one you forgot to add in.
- A CYP3A4 inhibitor is on board — raising the trazodone level, and with it the QT effect.
- The patient is older — reduced clearance, more baseline risk factors, more co-prescriptions.
- Potassium or magnesium is low — the substrate every QT drug exploits. Keep K⁺ > 4.0 and Mg²⁺ > 2.0.
Where trazodone sits among the antidepressants
A quick map of the class by QT risk. Note that the most interesting rows aren’t the obvious ones — trazodone’s mismatch between paper and practice, the SSRIs that endanger the QT without touching it themselves, and escitalopram sharing citalopram’s risk class.
| Antidepressant | QT risk | The catch |
|---|---|---|
| Sertraline | Lower | Cardiac first-line (SADHART); still a CYP2D6 inhibitor (less potent than fluoxetine/paroxetine) |
| Mirtazapine · Bupropion | Lower | Low direct QT — bupropion’s limiter is seizure threshold, not QT |
| Fluoxetine · Paroxetine · Fluvoxamine | Indirect | Don’t prolong QT themselves — they raise the levels of drugs that do (CYP) |
| Trazodone | Caution | “Conditional” on paper, FDA-warned in practice — TdP at ≤100 mg, and it hides as a sleep order |
| Venlafaxine | Caution (higher doses) | Dose-related QTc; raises HR/BP; toxic in overdose |
| Citalopram · Escitalopram | Known risk | Same CredibleMeds class — dose caps drop with age, liver, CYP |
| TCAs | Overdose-lethal | Modest at therapeutic dose; overdose is the killer |
| Gepirone (Exxua, 2024) | Strictest | Mandatory ECG; contraindicated if baseline QTc > 450 ms |
Clinical Pearl
When you tally a patient’s QT load, count the sleep order. Trazodone, quetiapine-for-sleep, and hydroxyzine are the three hypnotics that routinely fall out of the count because they’re not filed mentally as “real” psychotropics. Add them back in — the additive math doesn’t care what you prescribed the drug for.
Why it matters
QT prolongation is almost never the work of one drug. It’s the sum — a baseline interval that’s already a little long, an electrolyte that’s a little low, two or three agents each nudging repolarization. The danger of a silent contributor isn’t that it prolongs the QT dramatically on its own; it’s that it pushes a borderline interval over the edge while you’re looking at the other drugs. Trazodone is the textbook example: low-profile, ubiquitous, and quietly additive. Counting it costs nothing. Missing it can cost everything.
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