6 Sildenafil (Viagra) Interactions You Should Know About
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 medications that lower blood pressure, such as nitrates. It also interacts with alcohol and grapefruit juice.
Dizziness, headaches, or fainting could be symptoms of an interaction. Tell your healthcare team if you experience any of these symptoms. They can also check for potential sildenafil interactions in advance.
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Table of contents
Many men experience erectile dysfunction (ED), especially as they get older. Sildenafil (Viagra) is a first-choice medication to help get or maintain an erection.
But high blood pressure, heart disease, and prostate problems are also more common in men as they age. And many of the medications taken for these conditions interact with sildenafil. It’s not just medication that interacts with sildenafil, either. Combining sildenafil with alcohol or grapefruit juice can also cause problems.
Another form of sildenafil, Revatio, can be used for pulmonary arterial hypertension. It can interact with the same medications and substances as the sildenafil that’s used for ED (Viagra).
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Certain sildenafil interactions are serious and should be avoided altogether. For others, your prescriber may need to monitor you more closely. Share your medication list with your healthcare team. Then they can screen for interactions. Below, we’ll cover six common sildenafil interactions.
1. Nitrates
Nitrates are medications that treat heart conditions, such as chest pain (angina). Examples of nitrates are nitroglycerin (Nitrostat) and isosorbide mononitrate (Monoket). 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. With Viagra, this helps more blood flow to the penis for an erection. With Revatio, more blood is able to flow 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. That means that it should be avoided since it can cause harm. Instead, ask your prescriber to recommend a safer ED treatment.
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.
2. Alpha blockers
Alpha blockers treat conditions such as benign prostatic hyperplasia and high blood pressure. Examples of alpha blockers are tamsulosin (Flomax), alfuzosin (Uroxatral), and doxazosin (Cardura). Similar to sildenafil and nitrates, these medications work by relaxing blood vessels.
Combining an alpha blocker with sildenafil can cause low blood pressure. If you’re already taking an alpha blocker, your prescriber may have you take a lower sildenafil dose. And if you’re already taking sildenafil, they may have you take a lower dose of the alpha blocker.
Tell your prescriber if you experience 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.
3. Blood pressure medications
Nitrates and alpha blockers tend to have more severe interactions with sildenafil. But combining sildenafil with any blood pressure medication can cause an interaction.
For example, studies show that taking amlodipine (Norvasc), a calcium channel blocker, and sildenafil together can significantly lower blood pressure. Other blood pressure medications include angiotensin-converting enzyme inhibitors, angiotensin II receptor blockers, and diuretics.
If you’re taking any of these medications with sildenafil, your healthcare team may monitor your blood pressure more closely. And if your blood pressure is getting too low, they may need to adjust your dose of sildenafil.
4. Alcohol
Alcohol can interact with sildenafil in a few ways.
First, alcohol can cause or worsen ED. If you’re taking sildenafil to help with ED, alcohol may counteract its effects.
Second, alcohol widens blood vessels in the body, like sildenafil. So there’s a risk of low blood pressure when combining the two.
Finally, alcohol can worsen other sildenafil side effects. For example, headaches and facial flushing are common with both. They may be more likely to happen when they’re combined.
It’s best to avoid combining sildenafil and alcohol. But your prescriber can help determine if there’s a safe amount for you to drink.
5. Medications that affect liver proteins
Sildenafil is broken down by certain proteins in your liver. Some medications can block or overstimulate these proteins. This can affect the levels of sildenafil in the body.
Medications that may cause higher sildenafil levels include ritonavir (Norvir), clarithromycin, and ketoconazole. This interaction may make the side effects of sildenafil, such as headaches and flushing, more likely or more severe. If you’re taking one of these medications, your prescriber may start you on a lower sildenafil dose to be safe.
Medications and supplements that can cause lower sildenafil levels include rifampin (Rifadin), carbamazepine (Tegretol, Carbatrol), and St. John’s wort. When combined with these treatments, sildenafil may not work as well. Tell your prescriber if this happens since they may need to adjust your dose.
6. 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 could 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 safe to drink when you’re taking sildenafil.
Frequently asked questions about sildenafil interactions
It’s not recommended to take Viagra and Cialis (tadalafil) together. They’re both phosphodiesterase-5 inhibitors. This means they work the same way to treat ED. Typically, your prescriber will recommend taking only one of them.
Taking both medications increases your risk of side effects. These include 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 taking extra doses could increase your risk of side effects. Always follow your prescriber’s instructions to take Adderall and Viagra safely.
The bottom line
Sildenafil, also known as Viagra, can interact with many medications and substances. Examples include nitrates, alpha blockers, and blood pressure medications. It also interacts with alcohol, grapefruit juice, and medications that affect liver proteins.
Many sildenafil interactions can result in worsening side effects. These include dizziness, headaches, and flushing. Others can make this erectile dysfunction treatment less effective. Your prescriber and pharmacist can help you avoid and manage sildenafil interactions.
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References
Bryant Ranch Prepack. (2024). Sildenafil citrate- sildenafil tablet, film coated [package insert].
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.
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