Viagra (sildenafil) has one absolutely dangerous interaction and several that need caution. The critical one is with nitrates, which can cause a life-threatening drop in blood pressure. Others — certain blood-pressure drugs, some antibiotics and antifungals, and a few HIV medicines — call for dose adjustment or monitoring. This article summarises what interacts with sildenafil and why.
It belongs in our erectile dysfunction and sexual dysfunction solutions section.
The one to never combine: nitrates
Nitrates — used for chest pain (angina), including nitroglycerin sprays and tablets — must never be taken with sildenafil. Both lower blood pressure, and together they can cause a sudden, dangerous fall that may lead to fainting or worse. This is an absolute contraindication, not a "be careful".
Drugs that need caution
Several medicines raise sildenafil levels by slowing its breakdown, increasing side-effect risk. These include some antibiotics (macrolides like clarithromycin), antifungals (ketoconazole, itraconazole) and certain HIV protease inhibitors. Alpha-blockers and other blood-pressure medicines can add to the blood-pressure-lowering effect.
| Drug group | Concern |
|---|---|
| Nitrates | dangerous BP drop — never combine |
| Alpha-blockers / BP drugs | added BP lowering |
| Macrolide antibiotics | raise sildenafil levels |
| Azole antifungals | raise sildenafil levels |
| HIV protease inhibitors | raise sildenafil levels |
What about alcohol and recreational drugs?
Heavy alcohol adds to the blood-pressure effect and can make erections harder, so moderation matters. Recreational "poppers" (amyl nitrite) are nitrates and carry the same deadly risk as prescription nitrates — they must never be combined with sildenafil.
How are interactions managed?
For the cautionary drugs, a doctor may lower the sildenafil dose, separate the timing or choose a different option. The nitrate combination, by contrast, is simply off-limits. This is why a full medication list — including over-the-counter and recreational substances — is essential, as also discussed for Viagra with antibiotics.
The bottom line
Most men take sildenafil safely, but the nitrate rule is non-negotiable and a handful of other drugs need a dose tweak. Always tell your doctor and pharmacist everything you take. For how the body clears the drug, see the half-life of Viagra.
Do other ED drugs share these interactions?
Largely yes. Tadalafil (Cialis), vardenafil and avanafil belong to the same PDE-5 class and carry the same absolute ban on nitrates and the same cautions with strong enzyme inhibitors and blood-pressure drugs. Switching brands does not escape the rules — if nitrates are off-limits with Viagra, they are off-limits with Cialis too. The practical takeaway is that the interaction list travels with the drug class, not the brand name, so the same full-disclosure conversation with your doctor applies whichever of these medicines you use.
Related: Viagra with antibiotics. Clearance: Half-life of Viagra. Kidneys: Can Viagra affect kidneys?
Frequently asked questions
- What must never be combined with Viagra?
- Nitrates of any kind, including poppers — the combination can cause a dangerous drop in blood pressure.
- Which drugs need caution?
- Alpha-blockers, some antibiotics and antifungals, and certain HIV medicines, which may need a dose adjustment.
- Does alcohol interact?
- Heavy alcohol adds to the blood-pressure effect and can reduce the result; moderate it.