Sildenafil interactions: what to avoid and why
Sildenafil interactions can cause dangerously low blood pressure with nitrates and some other drugs. Know what to avoid and when to call.
Key facts
- Sildenafil is $69.67/month (billed $209 every 90 days), charged only after a clinician approves it.
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Sildenafil is a prescription medicine used for erectile dysfunction (ED) and, under a different brand and dosing, pulmonary arterial hypertension. The main safety concern is sildenafil interactions with other drugs that also lower blood pressure or change how your body breaks sildenafil down. This guide explains the most important interactions to know, what symptoms to watch for, and when to get urgent help. If you are unsure about a specific medication or supplement, Vitals Vault can help you start with labs or questions for a clinician supported plan.
- Sildenafil interactions are most dangerous with nitrates and riociguat because blood pressure can drop too low.
- Some HIV and antifungal medicines and certain antibiotics can raise sildenafil levels and side effect risk.
- Alpha blockers and other blood pressure medicines can add to dizziness or fainting risk, especially at first.
- Avoid grapefruit products unless your clinician says it is safe, because levels may increase.
Do any medications interact with sildenafil?
Sildenafil interactions: what to avoid or review
Nitrates (nitroglycerin)
Do not use sildenafil with any form of nitrates, including nitroglycerin. Both widen blood vessels, and together they can cause a large blood pressure drop that may lead to fainting, heart attack, or stroke. If you have chest pain after taking sildenafil, seek emergency care and tell responders you took sildenafil.
Riociguat
Do not take sildenafil with riociguat (a medicine for certain types of pulmonary hypertension). The combination can cause low blood pressure and fainting. Your clinician should choose a safer alternative if you need treatment for both conditions.
Alpha blockers
Alpha blockers (for prostate symptoms or high blood pressure) can add to sildenafil's blood pressure lowering effects. This can cause dizziness or lightheadedness, especially when standing up. Your clinician may adjust timing or dose and may ask you to be stable on one medicine before adding the other.
Strong CYP3A4 inhibitors
Some medicines can raise sildenafil levels by slowing its breakdown. Examples include certain HIV protease inhibitors (such as ritonavir) and some antifungals (such as ketoconazole or itraconazole). Higher levels can increase side effects like flushing, headache, low blood pressure, and vision changes, so your prescriber may limit sildenafil dosing or choose another option.
Some antibiotics
Certain antibiotics, including macrolides such as erythromycin, can increase sildenafil exposure. If you need an antibiotic, ask whether it is expected to interact and what symptoms should prompt a call. Do not change your medicines on your own.
Grapefruit products
Grapefruit juice can increase sildenafil levels by affecting the same enzyme pathway used to metabolize it. That can make side effects more likely in some people. If grapefruit is part of your routine, ask your clinician whether you should avoid it around the time you use sildenafil.
| Medication or category | Why it matters | What to do |
|---|---|---|
| Nitrates (including nitroglycerin) | Can cause dangerous blood pressure drop | Do not combine; get emergency help for chest pain |
| Riociguat | Additive blood pressure lowering | Do not combine; clinician should choose an alternative |
| Alpha blockers | More dizziness or fainting risk | Review timing and dosing with your clinician |
| HIV protease inhibitors (example: ritonavir) | Can greatly increase sildenafil levels | Clinician may restrict dosing or avoid combination |
| Azole antifungals (example: ketoconazole) | Can increase sildenafil levels | Ask about safer alternatives or monitoring |
| Macrolide antibiotics (example: erythromycin) | Can increase sildenafil levels | Check with prescriber; watch for side effects |
Lisinopril and Viagra
Lisinopril is a blood pressure medicine (an ACE inhibitor). Sildenafil can also lower blood pressure, so taking them together may increase the chance of lightheadedness in some people, especially when you first start or if you are dehydrated. This is not the same level of risk as nitrates, but it is still worth confirming with your clinician.
Other ED medicines
Avoid using sildenafil with other PDE5 inhibitors used for ED, such as tadalafil or vardenafil, unless a clinician specifically directs it. Combining them can increase side effects and blood pressure lowering. If one option is not working, a clinician can help you switch safely rather than stack medications.
Alcohol and recreational drugs
Alcohol can worsen dizziness and low blood pressure symptoms and can also make erections harder to achieve. Some recreational drugs and "poppers" (often containing nitrates) are especially dangerous with sildenafil. If you use any substances, tell your clinician so they can help you reduce risk.
When to call a clinician or get urgent care
Call 911 for chest pain
Chest pain, pressure, or shortness of breath can be a medical emergency. If you have taken sildenafil and develop chest pain, do not take nitroglycerin on your own. Seek emergency care and tell the care team you used sildenafil so they can choose safe treatments.
Urgent: fainting or severe dizziness
If you faint, feel like you might pass out, or have severe dizziness, especially after standing, get urgent medical help. This can be a sign your blood pressure is too low, which is more likely when sildenafil is combined with other blood pressure lowering medicines.
Urgent: vision or hearing changes
Stop what you are doing and seek urgent evaluation for sudden vision loss, sudden decrease in vision, or sudden hearing loss or ringing in the ears. These events are rare but are listed warnings for PDE5 inhibitors and need prompt medical attention.
Same day: prolonged erection
Get medical help right away for an erection that lasts more than 4 hours (priapism). Waiting can lead to permanent damage. This risk may be higher if sildenafil levels rise due to interacting medicines.
Schedule a review of your med list
If you start or stop an antibiotic, antifungal, HIV medicine, or an alpha blocker, ask for an interaction check before using sildenafil again. Bring a full list, including over the counter drugs and supplements. Your pharmacist can also help screen for interactions.
Pro tips for safer use
Keep an updated med list
Include as needed drugs like nitroglycerin, inhalers, and migraine medicines.
Ask about interaction timing
Some interactions depend on how recently you took another medicine, especially nitrates.
Avoid surprise nitrates
Some recreational "poppers" contain nitrates and are unsafe with sildenafil.
Be cautious with grapefruit
If you use grapefruit products, confirm whether you should avoid them.
Report unusual symptoms early
Severe flushing, faintness, vision changes, or prolonged erection need prompt help.
Frequently Asked Questions
What are the most dangerous sildenafil interactions?
The most dangerous sildenafil interactions are with nitrates (including nitroglycerin) and with riociguat, because blood pressure can drop to unsafe levels. Tell every clinician and pharmacist you see that you use sildenafil, even if it is only as needed.
What drugs not to take with Viagra?
Do not take sildenafil (the drug in Viagra) with nitrates or riociguat. Also review alpha blockers, certain HIV medicines, some antifungals, and some antibiotics with your prescriber because they can increase low blood pressure risk or raise sildenafil levels.
Can you take lisinopril and Viagra together?
Lisinopril and sildenafil can both lower blood pressure, so some people may feel lightheaded, especially when starting or if dehydrated. It is not the same absolute contraindication as nitrates, but you should confirm safety and timing with your clinician.
Why is sildenafil and nitroglycerin dangerous?
Sildenafil and nitroglycerin both relax blood vessels. Together they can cause a severe drop in blood pressure that may lead to fainting or serious heart complications. If you have chest pain after sildenafil, seek emergency care and tell responders you took it.
Does grapefruit interact with sildenafil?
Grapefruit products can increase sildenafil levels by affecting how your body metabolizes it. That may increase side effects for some people. Ask your clinician whether you should avoid grapefruit around the time you use sildenafil.