The 19 QT-Prolonging Drugs Every ADHD Prescriber Needs to Know About
When we talk about drug safety in ADHD prescribing, the conversation usually starts with cardiovascular contraindications — hypertension, structural heart disease, arrhythmias. These are the headline stops. Every prescriber knows them.
What gets less attention is the interaction risk that sits just below that threshold. The patient who doesn't have a cardiac diagnosis but is on a medication that prolongs the QT interval. The patient who is on two QT-prolonging drugs and wants to start atomoxetine. The patient whose citalopram dose puts them in the moderate risk category but not the absolute stop category.
These are the grey areas where prescribers need to make informed, documented decisions. And to do that, you need to know exactly which drugs carry QT risk — and how much.
What is QT prolongation and why does it matter in ADHD prescribing?
The QT interval represents the time it takes for the heart's ventricles to depolarise and repolarise after each beat. When this interval is prolonged — whether congenitally or drug-induced — the risk of a potentially fatal ventricular arrhythmia called Torsades de Pointes increases.
In ADHD prescribing, QT prolongation is most relevant to two medications:
Atomoxetine (Strattera) — a non-stimulant SNRI that carries its own QT prolongation risk and should not be combined with other QT-prolonging agents without careful assessment. The SPC advises caution with drugs known to prolong QT.
Lisdexamfetamine (Elvanse Adult) — while stimulants are not themselves significant QT prolongers, their cardiovascular effects in combination with existing QT-prolonging drugs can increase overall cardiac risk and warrant review.
For both drugs, the national shared care protocol is clear: a full medication review is required before initiation, with specific attention to QT-prolonging agents.
The 19 drugs — tiered by risk
This is not an exhaustive pharmacological list. This is a clinically practical list of the drugs most commonly encountered in an adult ADHD prescribing population, tiered by the level of concern they should trigger.
High risk — ECG required before initiating
These drugs carry significant QT prolongation risk. If your patient is taking any of these, obtain an ECG and document the result before initiating atomoxetine or reassess the clinical picture entirely.
Haloperidol
Droperidol
Thioridazine
Pimozide
Methadone
Sotalol
Amiodarone
Moderate risk — review and document
These drugs prolong QT to a clinically meaningful degree. They do not automatically prevent initiation but require documented clinical review, consideration of baseline QTc, and a clear rationale in the notes.
Citalopram
Escitalopram
Quetiapine
Olanzapine
Risperidone
Chlorpromazine
Erythromycin
Clarithromycin
Ondansetron
Domperidone
Review — flag and consider
These carry lower but non-negligible QT risk. Flag in the clinical record and factor into the overall cardiac risk assessment.
Fluconazole
Lithium
The SSRI question
Citalopram and escitalopram deserve particular attention because they are among the most commonly prescribed antidepressants in the UK and they carry the highest QT prolongation risk of all the SSRIs.
The Medicines and Healthcare products Regulatory Agency (MHRA) issued guidance capping citalopram doses specifically because of QT risk — 40mg maximum for adults, 20mg for those over 65.
A patient on citalopram 40mg who wants to start atomoxetine requires a careful, documented review. This is not a hard stop in every case, but it is a decision that needs to be made explicitly and recorded clearly — not assumed to be fine.
Fluoxetine, sertraline, and paroxetine carry lower QT risk than citalopram and escitalopram, but they introduce a different concern in the context of ADHD prescribing — serotonin syndrome risk with stimulants and atomoxetine, which is a separate clinical consideration.
Serotonin syndrome — a brief note
While not strictly a QT issue, serotonin syndrome risk is worth addressing here because it often appears in the same part of the pre-initiation review.
Atomoxetine inhibits norepinephrine reuptake and can contribute to serotonergic effects when combined with SSRIs, SNRIs, tramadol, or MAOIs. The risk is dose-dependent and patient-specific, but it should be flagged whenever a patient is on a serotonergic agent.
MAOIs are the most serious concern — there is an absolute contraindication to atomoxetine within 14 days of stopping an MAOI. The seven MAOIs most relevant to clinical practice are phenelzine, tranylcypromine, isocarboxazid, moclobemide, selegiline, rasagiline and safinamide. Selegiline patches used for Parkinson's disease are sometimes overlooked — worth checking explicitly.
What good documentation looks like
Identifying a QT-prolonging drug in a patient's medication list is the first step. Documenting what you did with that information is the part that protects you.
A defensible record should show:
Which QT-prolonging drug(s) were identified
Which risk tier they fall into
Whether an ECG was obtained and what it showed, or a clear rationale for why one was not obtained
The clinical decision made — proceed, review, defer, or do not initiate
Any counselling given to the patient
"Drug interactions checked — suitable to proceed" is not a defensible record. The specific drugs identified and the specific clinical reasoning are what make documentation meaningful.
The practical challenge
Most prescribers can recall the major QT-prolonging drugs. Fewer can recall all nineteen in a busy clinic, across every patient, every time. And the documentation requirement means that even when the clinical check is done correctly, the record often doesn't reflect it.
This is the gap that structured pre-initiation screening is designed to close — not to replace clinical knowledge, but to ensure it is applied consistently and recorded reliably every time.
A note on tools
The QT-prolonging drug list above is incorporated into ADHD Rx Screening, the clinical decision support tool I developed for adult ADHD prescribers. When reviewing a patient's medications, prescribers can select from the full named list of QT-prolonging drugs, with each one flagged by risk tier and accompanied by a prompt for the appropriate clinical response.
If you'd like to see how it works, there's a short demo at vimeo.com/1182878511 and a 14-day free trial at focusgentlyclinical.solutions — no card required.
This article is intended for qualified healthcare professionals. It is not a substitute for current clinical guidelines, the BNF, or individual drug SPCs. Always consult the most up-to-date prescribing information before making clinical decisions.
