Drug interactions
Prazosin + Tadalafil
Severity: Major
Prazosin and Tadalafil: major interaction.
Last updated Sources: US FDA label
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Prazosin is an alpha-1 blocker and tadalafil adds vasodilation, so the combination can cause significant orthostatic hypotension, dizziness or syncope. The risk is greatest at initiation or after dose increases.
What this interaction means in plain words
Prazosin and Tadalafil can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Prazosin belongs to Genitourinary; Tadalafil belongs to Genitourinary.
Why it happens
Additive vasodilation from PDE5 inhibition and alpha-1 adrenergic blockade.
What to do
Ensure the patient is stable on prazosin and start tadalafil at the lowest dose, separating dosing where feasible. Monitor standing blood pressure and counsel on syncope risk.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
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References
Other interactions of Tadalafil
- Amyl nitrite + Tadalafil Contraindicated
- Isosorbide dinitrate + Tadalafil Contraindicated
- Isosorbide mononitrate + Tadalafil Contraindicated
- Nitroglycerin po + Tadalafil Contraindicated
- Nitroglycerin rectal + Tadalafil Contraindicated
- Nitroglycerin sublingual + Tadalafil Contraindicated
Other interactions of Prazosin
- Alfuzosin + Prazosin Major
- Amifostine + Prazosin Major
- Avanafil + Prazosin Major
- Doxazosin + Prazosin Major
- Dutasteride-tamsulosin + Prazosin Major
- Phenoxybenzamine + Prazosin Major
Frequently asked questions
Can I take Prazosin with Tadalafil?
MediHelp rates the interaction as major. Prazosin and Tadalafil can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Prazosin is an alpha-1 blocker and tadalafil adds vasodilation, so the combination can cause significant orthostatic hypotension, dizziness or syncope. The risk is greatest at initiation or after dose increases.
How serious is the interaction between Prazosin and Tadalafil?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Ensure the patient is stable on prazosin and start tadalafil at the lowest dose, separating dosing where feasible. Monitor standing blood pressure and counsel on syncope risk.
What other medicines interact with Tadalafil?
MediHelp also lists interactions of Tadalafil with, for example, Amyl nitrite, Isosorbide dinitrate, Isosorbide mononitrate. The full list is on the Tadalafil page.
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