Key takeaways:
Sildenafil (Viagra) is a medication used to treat erectile dysfunction. It’s also available under the brand name Revatio for pulmonary arterial hypertension.
Sildenafil interacts with nitrates, alpha blockers, and riociguat (Adempas). It also interacts with blood pressure medications, alcohol, and grapefruit juice.
Dizziness, headaches, or fainting can be symptoms of a sildenafil interaction. Tell your healthcare team if you experience any of these symptoms.
Share a list of medications you’re currently taking with your healthcare team in advance so they can check for potential sildenafil interactions.
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Many men experience erectile dysfunction (ED), especially as they get older. Sildenafil (Viagra) is a first-choice medication to help achieve or maintain an erection.
Likewise, high blood pressure, heart disease, and prostate problems also become more common for men as they age. This can make ED treatment tricky, since many of the medications taken for these conditions interact with sildenafil. Here, we’ll discuss more about sildenafil’s common interactions and how you and your healthcare team can manage them together.
Sildenafil (Viagra) interactions at a glance
Certain sildenafil interactions are serious and should be avoided altogether. Other interactions are less serious, but your prescriber may still need to monitor you closely. The best way to manage potential sildenafil interactions is by sharing your medication list with your healthcare team for review.
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While this is not a complete list, sildenafil can interact with the following medications and substances:
Nitrates, such as nitroglycerin (Nitrostat) and isosorbide mononitrate (Monoket)
Soluble guanylate cyclase (sGC) stimulators, such as riociguat (Adempas)
Alpha blockers, such as tamsulosin (Flomax), alfuzosin (Uroxatral), and doxazosin (Cardura)
Blood pressure medications, such as lisinopril (Zestril Qbrelis), losartan (Cozaar, Arbli), and amlodipine (Norvasc)
Alcohol
Ritonavir (Norvir)
Paxlovid (nirmatrelvir / ritonavir)
Clarithromycin
Ketoconazole
Rifampin (Rifadin)
Carbamazepine (Tegretol, Carbatrol)
St. John’s wort
Grapefruit juice
Good to know: Another form of sildenafil, Revatio, can be taken for pulmonary arterial hypertension. It can interact with the same medications and substances as the sildenafil that’s taken for ED (Viagra).
Below, we take a closer look at seven potential sildenafil interactions and how they can be managed.
1. Nitrates
Nitrates, such as nitroglycerin, are medications that treat heart conditions like chest pain (angina). They work by widening the blood vessels throughout the body. This helps increase blood flow to your heart, but it can also lower your blood pressure.
Sildenafil also works by widening blood vessels. Viagra helps increase blood flow to the penis, which makes it easier to get an erection. Revatio helps blood flow more easily to your lungs. But when either is combined with a nitrate, this can result in dangerously low blood pressure.
Taking sildenafil with nitrates is contraindicated, which means that it should be avoided completely because it can cause harm. Instead, ask your prescriber to recommend a safer ED treatment for you.
2. Alpha blockers
Alpha blockers, such as tamsulosin, alfuzosin, and doxazosin, are used to treat conditions such as benign prostatic hyperplasia and high blood pressure. Similar to sildenafil and nitrates, these medications work by relaxing your blood vessels.
Combining an alpha blocker with sildenafil can cause low blood pressure. If you’re already taking an alpha blocker, your prescriber may suggest you take a lower dose of sildenafil. And if you’re already taking sildenafil, they may suggest you take a lower dose of the alpha blocker.
Tell your prescriber if you experience any symptoms of low blood pressure (hypotension). This includes feeling dizzy or lightheaded. And get immediate medical attention if you feel as though you’re going to pass out.
What to expect: Do you get headaches after taking Viagra? Learn more about Viagra side effects, why they happen, and what you can do to manage them.
Pharmacist tips: If you’ve been prescribed Viagra, you may have questions about when and how to take it. Pharmacists discuss how long Viagra takes to work and other tips to help you get the best results.
Frequently asked questions: Get answers on common questions about Viagra, including how long it stays in your system and how it works.
3. Blood pressure medication
Nitrates and alpha blockers tend to have more severe interactions with sildenafil. But combining sildenafil with any blood pressure medication can cause an interaction. Common examples include amlodipine, lisinopril, and losartan.
Taking blood pressure medication doesn’t necessarily mean you need to avoid sildenafil. In this case, your healthcare team may monitor your blood pressure more closely. They may need to adjust your sildenafil dose if your blood pressure gets too low.
4. sGC stimulators such as riociguat
Riociguat is an sGC stimulator used to treat certain types of pulmonary hypertension. It works on the same pathway as sildenafil to relax blood vessels and improve blood flow. Taking riociguat and sildenafil together can cause a dangerous drop in blood pressure.
Due to this risk, sildenafil and riociguat should never be taken together. If you’re prescribed either medication, be sure to tell your healthcare team about all the treatments and medications you’re currently taking. They can suggest a safer alternative, depending on your needs.
5. Alcohol
It’s best to avoid or minimize alcohol consumption while taking sildenafil. This is because alcohol can interact with sildenafil in a few ways:
Alcohol can cause or worsen ED. If you’re taking sildenafil to help with ED, alcohol may counteract its effects.
Alcohol can affect your blood pressure. Alcohol, like sildenafil, widens blood vessels in the body. So there’s a risk of low blood pressure when combining the two. Heavy alcohol consumption can also increase the risk of developing high blood pressure.
Alcohol can worsen other sildenafil side effects. For example, headaches and facial flushing are common side effects of both substances. They may be more likely to happen when alcohol and sildenafil are combined.
Everyone responds to alcohol and medications differently. Your prescriber can help determine whether it’s safe for you to drink while taking sildenafil, and if so, how much is appropriate.
6. Medications that affect liver proteins
Sildenafil is broken down by certain proteins in your liver. Some medications can block these proteins, resulting in higher sildenafil levels and a greater risk of side effects. Other medications can cause your body to break down sildenafil faster, making it less effective.
In either case, your prescriber may need to adjust your dose of sildenafil if you’re taking any of these medications:
| Examples of medications that increase sildenafil levels | Examples of medications that lower sildenafil levels |
|---|---|
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7. Grapefruit juice
Grapefruit juice can affect specific liver proteins, similar to the medications listed above. But the effects tend to vary from person to person and are less predictable.
In theory, drinking a lot of grapefruit juice may cause higher levels of sildenafil in the body. And this could cause a worsening of side effects, such as low blood pressure and headaches. Your prescriber can help you determine how much grapefruit juice is OK for you to drink while taking sildenafil.
Frequently asked questions
It’s not recommended to take Viagra and Cialis (tadalafil) together. They’re both phosphodiesterase-5 inhibitors, which means they work the same way to treat ED. Typically, your prescriber will recommend taking only one of them at a time.
Taking both medications increases your risk of side effects, including low blood pressure. It isn’t clear if there are beneficial effects of combining Viagra and Cialis. Some studies have suggested a potential benefit, but more research is needed.
There aren’t significant interactions between Adderall (amphetamine salt combo) and Viagra. It’s likely safe to take these medications together. But it’s good to be aware that Adderall may raise blood pressure, while Viagra can lower it. Always follow your prescriber’s instructions to take Adderall and Viagra safely.
Sildenafil can cause side effects such as headaches, flushing, and an upset stomach. Not everyone experiences these side effects, but here are a few ways to help reduce your risk:
Take the lowest effective dose. If you have bothersome side effects, ask your prescriber about trying a lower dose of sildenafil.
Avoid alcohol. Drinking alcohol while taking sildenafil can worsen side effects such as dizziness, headaches, and low blood pressure.
Watch for other medications that lower blood pressure. Some medications can cause dangerously low blood pressure if taken with sildenafil. Others should be taken with caution. Share your medication list with your healthcare team to help identify potential harmful interactions.
It’s not recommended to take Viagra and Cialis (tadalafil) together. They’re both phosphodiesterase-5 inhibitors, which means they work the same way to treat ED. Typically, your prescriber will recommend taking only one of them at a time.
Taking both medications increases your risk of side effects, including low blood pressure. It isn’t clear if there are beneficial effects of combining Viagra and Cialis. Some studies have suggested a potential benefit, but more research is needed.
There aren’t significant interactions between Adderall (amphetamine salt combo) and Viagra. It’s likely safe to take these medications together. But it’s good to be aware that Adderall may raise blood pressure, while Viagra can lower it. Always follow your prescriber’s instructions to take Adderall and Viagra safely.
Sildenafil can cause side effects such as headaches, flushing, and an upset stomach. Not everyone experiences these side effects, but here are a few ways to help reduce your risk:
Take the lowest effective dose. If you have bothersome side effects, ask your prescriber about trying a lower dose of sildenafil.
Avoid alcohol. Drinking alcohol while taking sildenafil can worsen side effects such as dizziness, headaches, and low blood pressure.
Watch for other medications that lower blood pressure. Some medications can cause dangerously low blood pressure if taken with sildenafil. Others should be taken with caution. Share your medication list with your healthcare team to help identify potential harmful interactions.
The bottom line
Sildenafil, also known as Viagra, can interact with many medications and substances. Examples include nitrates, alpha blockers, and blood pressure medications. Sildenafil also interacts with alcohol, grapefruit juice, and medications that affect liver proteins.
Many sildenafil interactions can worsen side effects. These include dizziness, headaches, and flushing. Other interactions may make this erectile dysfunction treatment less effective. Your prescriber and pharmacist can help you avoid and manage interactions with sildenafil.
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References
Dhaliwal, A., et al. (2023). PDE5 inhibitors. StatPearls.
Mykoniatis, I., et al. (2021). Assessment of combination therapies vs monotherapy for erectile dysfunction: A systematic review and meta-analysis. JAMA Network Open.
Torrent Pharmaceuticals. (2025). Sildenafil- sildenafil tablet, film coated [package insert].
