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Viagra Interactions: What to Avoid

Documented interactions for Viagra (sildenafil). Each entry cites the prescribing information or FDA safety communication it is based on.

2 contraindicated4 moderate

Interaction summary

SeverityInteracts withClassConcern
ContraindicatedNitrates (nitroglycerin, isosorbide)Nitrate vasodilatorSildenafil with nitrates is absolutely contraindicated
ContraindicatedRiociguat (soluble guanylate cyclase stimulator)Soluble guanylate cyclase stimulatorSildenafil with soluble guanylate cyclase stimulators is contraindicated
ModerateAlcohol (ethanol)CNS depressantSildenafil with alcohol: compounded blood-pressure lowering
ModerateAlpha-blockers (tamsulosin, doxazosin, terazosin)Alpha-adrenergic blockerSildenafil with alpha-blockers: additive blood-pressure lowering
ModerateOther QT-prolonging drugs (class IA/III antiarrhythmics, some macrolides, haloperidol, methadone, ondansetron)QT-prolonging agentSildenafil and QT-related cardiac considerations
ModerateStrong CYP3A4 inhibitors (ketoconazole, itraconazole, clarithromycin, ritonavir, grapefruit juice)CYP3A4 inhibitorStrong CYP3A4 inhibitors raise sildenafil exposure

Detailed interactions

Contraindicated

Sildenafil with nitrates is absolutely contraindicated

With: Nitrates (nitroglycerin, isosorbide) Nitrate vasodilator

Why it happens

Nitrates and sildenafil both increase cyclic GMP in vascular smooth muscle. The combined vasodilation is far greater than either alone.

What can happen

Severe, life-threatening hypotension. Patients have required emergency treatment and have died.

What to do

The combination is an absolute contraindication. Never take sildenafil and nitrates within 24 hours of each other. Carry the nitrate prescription with you and tell any prescriber you are taking sildenafil.

Basis: Sildenafil citrate tablets prescribing information, Contraindications: Nitrates. source

Contraindicated

Sildenafil with soluble guanylate cyclase stimulators is contraindicated

With: Riociguat (soluble guanylate cyclase stimulator) Soluble guanylate cyclase stimulator

Why it happens

Additive cGMP-mediated vasodilation.

What can happen

Hypotension.

What to do

Do not combine.

Basis: Sildenafil citrate tablets prescribing information, Contraindications. source

Moderate

Sildenafil with alcohol: compounded blood-pressure lowering

With: Alcohol (ethanol) CNS depressant

Why it happens

Alcohol lowers blood pressure and sildenafil does as well.

What can happen

Dizziness, lightheadedness, fainting, and impaired judgment.

What to do

Labeling advises against drinking alcohol while taking sildenafil.

Basis: Sildenafil citrate tablets prescribing information, Adverse Reactions. source

Moderate

Sildenafil with alpha-blockers: additive blood-pressure lowering

With: Alpha-blockers (tamsulosin, doxazosin, terazosin) Alpha-adrenergic blocker

Why it happens

Both drugs lower blood pressure through vascular smooth muscle relaxation.

What can happen

Symptomatic hypotension, including fainting.

What to do

Labeling describes starting alpha-blocker therapy after sildenafil has been established, and separating doses.

Basis: Sildenafil citrate tablets prescribing information, Drug Interactions. source

Moderate

Sildenafil and QT-related cardiac considerations

With: Other QT-prolonging drugs (class IA/III antiarrhythmics, some macrolides, haloperidol, methadone, ondansetron) QT-prolonging agent

Why it happens

Sildenafil is generally not QT-prolonging, but rare serious cardiovascular events have been reported.

What can happen

Labeling notes that cardiovascular disease predisposes patients to risk during sexual activity.

What to do

Patients with heart disease should discuss sexual activity with a clinician before taking sildenafil.

Basis: Sildenafil citrate tablets prescribing information, Warnings and Precautions. source

Moderate

Strong CYP3A4 inhibitors raise sildenafil exposure

With: Strong CYP3A4 inhibitors (ketoconazole, itraconazole, clarithromycin, ritonavir, grapefruit juice) CYP3A4 inhibitor

Why it happens

CYP3A4 metabolizes sildenafil; inhibition slows clearance.

What can happen

Increased exposure and adverse effects such as headache, flushing, and visual changes.

What to do

Labeling recommends reducing the sildenafil dose when a strong CYP3A4 inhibitor is used.

Basis: Sildenafil citrate tablets prescribing information, Drug Interactions and Dosage. source

Common questions

What should I know about Viagra interactions?

We have documented 6 interaction classes for Viagra in our dataset. Usually avoided, or used only with explicit prescriber oversight and close monitoring. The most serious items on this page are marked contraindicated or major.

Can I take Viagra with alcohol?

Alcohol interacts with most of the medications on this site because it adds to sedation and slows breathing. For the specific documented risk, see the relevant entry above. The general rule from labeling is to avoid alcohol.

Does an empty result mean Viagra is safe with other drugs?

No. An empty result only means our curated dataset has no matching rule. A pharmacist can run a full interaction screen against every medication and supplement you take.

Related

Editorial Review Board

Clinical review by licensed pharmacists (PharmD)

Every page on this site is reviewed against current FDA prescribing information, DailyMed labelling, DEA scheduling regulations and MedlinePlus monographs before publication. Reviewers have no commercial relationship with any manufacturer or pharmacy.

Last substantive review: October 01, 2026

Sources & references

MedlinePlus drug information (National Library of Medicine)
PubChem compound record (National Institutes of Health)

Important

This site provides educational information only and does not sell, prescribe or dispense medications. Always consult a licensed healthcare provider. This page is not medical advice.