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Viagra drug interactions

Viagra · sildenafil · by Pfizer

Reviewed by the glpzoom Editorial Team against primary clinical sources — FDA labeling, peer-reviewed trials, and specialty-society guidelines.
Content current as of June 2026; updated when guidance or availability changes.
Most clinically critical: nitrates (nitroglycerin, isosorbide) — combination can cause severe, life-threatening blood pressure drop. Never use Viagra within 24 hours of a nitrate. Caution with alpha-blockers (doxazosin, terazosin — hypotension risk; separate doses by at least 4 hours). Caution with CYP3A4 inhibitors (ketoconazole, ritonavir, erythromycin — increase Viagra blood levels; dose reduction needed). Generally safe with most other medications; disclose all to prescriber.

Interaction lookup

Search by medication name or drug class to see clinically meaningful Viagra interactions.

  • Nitrates (nitroglycerin, isosorbide)

    Major

    Class: nitrate

    Severe, life-threatening hypotension. Never combine within 24 hours.

  • Alpha-blockers (doxazosin, terazosin)

    Moderate

    Class: alpha-blocker

    Hypotension risk. Separate doses by 4+ hours; start with lower sildenafil dose.

  • Ketoconazole / Itraconazole

    Moderate

    Class: CYP3A4 inhibitor (azole antifungal)

    Significantly raises sildenafil levels — start at 25 mg.

  • Ritonavir / Protease inhibitors

    Major

    Class: CYP3A4 inhibitor

    Very large increase in sildenafil exposure — maximum 25 mg every 48 hours.

  • Erythromycin / Clarithromycin

    Moderate

    Class: macrolide

    Raises sildenafil levels; consider lower dose.

Editorial table from FDA labels + drug compendia. Not exhaustive. Discuss any concurrent medication, supplement, or condition with your prescriber before starting or stopping treatment.

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Frequently asked

What medications interact with Viagra?+

Most clinically critical: nitrates (nitroglycerin, isosorbide) — combination can cause severe, life-threatening blood pressure drop. Never use Viagra within 24 hours of a nitrate. Caution with alpha-blockers (doxazosin, terazosin — hypotension risk; separate doses by at least 4 hours). Caution with CYP3A4 inhibitors (ketoconazole, ritonavir, erythromycin — increase Viagra blood levels; dose reduction needed). Generally safe with most other medications; disclose all to prescriber.

Can I take Viagra with metformin?+

Viagra and metformin are commonly co-prescribed without major interaction concerns. GI side effects may be additive in some patients.

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