Viagra (sildenafil) is a prescription drug that’s used to treat erectile dysfunction (ED) in adults. Like other drugs, Viagra may have interactions.

Some interactions occur because one substance causes another substance to have a different effect than expected. For example, sometimes alcohol, another drug, or a supplement can affect how a drug acts in your body. Interactions can also occur if you have certain health conditions.

Keep reading to learn about Viagra’s possible interactions. And for more information about Viagra, including details about its uses, see this article.

Taking certain medications or other factors could raise your risk of harm if you take Viagra. In that case, your doctor may not prescribe Viagra for you. This is known as a contraindication. The list below includes contraindications of Viagra.

If you take a nitrate drug. Using Viagra together with a nitrate can cause your blood pressure to drop to dangerously low levels. Due to this risk, doctors won’t prescribe nitrate drugs and Viagra together. Examples of nitrates include nitroglycerin (Nitrostat, NitroMist) and isosorbide dinitrate (Isordil).

If you take a guanylate cyclase (GC) stimulator drug. Using Viagra together with a GC stimulator can result in your blood pressure dropping to dangerously low levels. Due to this risk, doctors won’t prescribe GC stimulators, such as riociguat (Adempas), and Viagra together.

If you’ve had an allergic reaction. If you have had an allergic reaction to Viagra or any of its ingredients, your doctor likely won’t prescribe Viagra. You can ask them about other treatments that may be better options for you.

Before you start taking Viagra, talk with your doctor if any of the factors above apply to you. Your doctor can determine whether Viagra is safe for you to take.

It’s possible for alcohol to interact with Viagra. But it may depend on how much alcohol you consume.

Both Viagra and alcohol can lower your blood pressure. So it’s thought that taking the two together could cause blood pressure to drop to very low levels.

If you drink alcohol, tell your doctor before you start taking Viagra. They can discuss with you how much alcohol, if any, is safe to drink while you’re taking the drug.

Before you start taking Viagra, tell your doctor and pharmacist about any prescription, over-the-counter, or other drugs you take. Sharing this information with them may help prevent possible medication interactions.

If you have questions about drug interactions that may affect you, talk with your doctor or pharmacist.

The chart below lists drugs that may interact with Viagra. Keep in mind that this chart does not include all drugs that may interact with Viagra. For more information about some of these interactions, see the “Drug interactions explained” section below.

Drug group or drug name Drug examples Interaction result with Viagra
nitrates nitroglycerin (Nitrostat, NitroMist)
• isosorbide dinitrate (Isordil)
can increase the risk of Viagra’s side effects* and the effect of nitrates
guanylate cyclase (GC) stimulators • riociguat (Adempas)
• vericiguat (Verquvo)
can increase the risk of Viagra’s side effects* and the effect of GC stimulators
alpha-blockers prazosin (Minipress)
doxazosin (Cardura)
terazosin
can increase the risk of Viagra’s side effects
blood pressure drugs, including:
angiotensin-converting enzyme (ACE) inhibitors
angiotensin II receptor blockers (ARBS)
diuretics (water pills)
amlodipine (Norvasc)
• lisinopril (Zestril)
• valsartan (Diovan)
hydrochlorothiazide (Microzide)
can increase the risk of Viagra’s side effects and the effect of blood pressure drugs
ritonavir (Norvir) can increase the effect of Viagra as well as the risk of side effects from this drug
erythromycin (Ery-Tab) can increase the effect of Viagra as well as the risk of side effects from this drug
certain antifungal drugs ketoconazole
• itraconazole (Sporanox, Tolsura)
can increase the effect of Viagra as well as the risk of side effects from this drug
other drugs for erectile dysfunction (ED) • tadalafil (Cialis)
• vardenafil (Levitra)
• avanafil (Stendra)
can increase the effect of Viagra as well as the risk of side effects from this drug
drugs for pulmonary arterial hypertension sildenafil (Revatio)
tadalafil (Adcirca, Alyq)
can increase the effect of Viagra as well as the risk of side effects from this drug

* For more information about this interaction, see the “When to avoid Viagra” section above.

Learn more about certain drug interactions that can occur with Viagra.

Interaction with alpha-blockers

Viagra may interact with alpha-blockers, as described below. Alpha-blockers are used to treat high blood pressure, benign prostatic hyperplasia (enlarged prostate), and certain other conditions.

What could happen Examples of alpha-blockers What you can do
can cause low blood pressure prazosin (Minipress)
doxazosin (Cardura)
terazosin
If you take an alpha-blocker, tell your doctor. If they agree it’s safe for you to take an alpha-blocker with Viagra, they may recommend you take a lower Viagra dose than usual. Or instead, they may prescribe a drug other than Viagra for your condition.

Interaction with blood pressure drugs

Viagra may interact with blood pressure drugs other than alpha-blockers (discussed just above). These are described below.

What could happen Examples of blood pressure medications What you can do
can cause low blood pressure amlodipine (Norvasc)
angiotensin-converting enzyme (ACE) inhibitors, such as lisinopril (Zestril)
angiotensin II receptor blockers (ARBS), such as valsartan (Diovan)
diuretics (water pills), such as hydrochlorothiazide (Microzide)
If you take blood pressure drugs, let your doctor know. They’ll likely want you to closely monitor your blood pressure. They’ll also recommend you watch out for any symptoms of low blood pressure.

Interaction with other drugs for erectile dysfunction

Viagra can interact with other drugs for erectile dysfunction (ED), as described below.

What could happen Examples of other medications for ED What you can do
• can cause low blood pressure
• may cause other serious side effects, such as priapism
• tadalafil (Cialis)
• vardenafil (Levitra)
• avanafil (Stendra)
Due to the risks involved, you should avoid using other ED drugs together with Viagra.

Viagra may have other interactions. They could occur with supplements, foods, vaccines, or even lab tests. See below for details.

Does Viagra interact with supplements?

Before you start taking Viagra, talk with your doctor and pharmacist about any supplements, herbs, and vitamins you take. Sharing this information with them may help you avoid possible interactions.

If you have questions about interactions that may affect you, talk with your doctor or pharmacist.

Viagra interactions with herbs

The herbal supplement St. John’s wort can interact with Viagra. Taking St. John’s wort may make Viagra less effective than usual.

Due to this risk, your doctor may adjust your Viagra dosage if you take this herbal supplement. They may also suggest that you stop using St. John’s wort.

Viagra and vitamins

There are currently no reports of Viagra interacting with vitamins. But this doesn’t mean that vitamin interactions won’t be recognized in the future.

For this reason, it’s still important to check with your doctor or pharmacist before you start taking a vitamin during Viagra treatment. They can let you know whether taking the vitamin with Viagra is safe.

Does Viagra interact with food?

Viagra may interact with grapefruit, including grapefruit juice. Grapefruit can increase levels of Viagra in your body, which may increase your risk of side effects.

It’s recommended that you avoid consuming grapefruit and any grapefruit products while taking Viagra. But if you consume grapefruit regularly and want to continue doing so, your doctor may lower your dosage of Viagra.

Does Viagra interact with vaccines?

There aren’t known interactions between Viagra and vaccines.

Does Viagra interact with lab tests?

Viagra isn’t known to interact with any lab tests.

Does Viagra interact with cannabis or CBD?

Cannabis (marijuana) and cannabis products, such as cannabidiol (CBD), have been specifically reported to interact with Viagra. Tetrahydrocannabinol (THC), a component of cannabis, may increase Viagra levels in your body. This could increase your risk of side effects, such as low blood pressure.

Before you start treatment with Viagra, tell your doctor and pharmacist if you take cannabis. By sharing this information with them, you may help prevent possible interactions.

Note: Cannabis is illegal at a federal level but is legal in many states to varying degrees.

Does Viagra interact with cannabis or CBD?

Cannabis (marijuana) and cannabis products, such as cannabidiol (CBD), have been specifically reported to interact with Viagra. Tetrahydrocannabinol (THC), a component of cannabis, may increase Viagra levels in your body. This could increase your risk of side effects, such as low blood pressure.

Before you start treatment with Viagra, tell your doctor and pharmacist if you take cannabis. By sharing this information with them, you may help prevent possible interactions.

Note: Cannabis is illegal at a federal level but is legal in many states to varying degrees.

Certain medical conditions or other health factors may increase the risk of interactions with Viagra. Before taking Viagra, talk with your doctor about your health history. They’ll determine whether Viagra is right for you.

Health conditions or other factors that might interact with Viagra include:

  • Heart problems or heart surgery in the past 6 months. Before taking Viagra, talk with your doctor if you have heart problems. This includes having high blood pressure or having had a heart attack. Also let them know if you’ve had heart surgery in the past 6 months. Your doctor can determine whether your heart is healthy enough for sex as well as taking Viagra. They may prescribe a lower Viagra dose. If the risks of taking the drug outweigh the benefits, they may not prescribe the drug to you.
  • Stroke. It may not be safe to use Viagra if you’ve had a stroke. Talk with your doctor about whether Viagra is safe for you to take.
  • Blood cell problems. Having blood cell problems, such as sickle cell anemia or leukemia, may increase your risk of priapism. This is a rare but serious side effect of Viagra. If you have blood cell problems, ask your doctor whether Viagra is safe for you to use.
  • Retinitis pigmentosa. In rare cases, Viagra can cause eye-related side effects. It’s not known whether people with retinitis pigmentosa are at higher risk of these side effects. If you have this eye condition, tell your doctor. They can discuss the benefits and risks of using Viagra with you.
  • Bleeding problems. Having bleeding problems, such as hemophilia, may increase your risk of bleeding as a side effect of Viagra. If you have bleeding problems, ask your doctor whether Viagra is safe for you to use.
  • Peptic ulcer. Having a peptic ulcer may increase your risk of bleeding as a side effect of Viagra. If you have this condition, ask your doctor whether Viagra is a safe treatment option for you.
  • Liver problems. Viagra levels can build up in the body of people with liver problems, increasing the risk of side effects. Before you take Viagra, tell your doctor if you have a liver problem, such as alcohol-related liver disease. Your doctor will likely prescribe a lower Viagra dose for you.
  • Severe kidney problems. Viagra levels can build up in the body of a person with a severe kidney problem, such as severe chronic kidney disease. This can increase the risk of side effects from the drug. If you have a severe kidney problem, your doctor will likely prescribe a lower Viagra dose for you.
  • Irregular penis shape. Having a condition that affects the shape of your penis may increase your risk of priapism as a side effect of Viagra. An example is Peyronie’s disease. Ask your doctor whether Viagra is safe for you to take.
  • Pregnancy. Viagra is not meant for use in females.* It’s unknown whether Viagra is safe to take during pregnancy.
  • Breastfeeding. Viagra is not meant for use in females. It’s unknown whether Viagra is safe to take during breastfeeding.
  • Allergic reaction. If you’ve had an allergic reaction to Viagra or any of its ingredients, your doctor will likely not prescribe Viagra. You can ask them about other treatments that may be better choices for you.

* In this article, we use the term “female” to refer to someone’s sex assigned at birth. For information about the difference between sex and gender, see this article.

Find answers to some frequently asked questions about Viagra and possible interactions.

Does Viagra interact with statins, such as Lipitor?

No, Viagra is not known to interact with statins, including atorvastatin (Lipitor).

Statin medications such as Lipitor are commonly prescribed to people with heart problems. Having heart problems sometimes makes it unsafe to take Viagra. But Lipitor itself isn’t known to interact with Viagra.

If you have heart problems, talk with your doctor or pharmacist about whether it’s safe for you to take Viagra.

Is it safe to take Viagra and doxycycline together?

Yes, Viagra and doxycycline (Acticlate, Doryx) are thought to be safe to take together. There have been no reports of an interaction between these medications.

Doxycycline is a kind of antibiotic medication. Viagra can interact with erythromycin (Ery-Tab), which is another antibiotic. Viagra can also interact with certain antifungal drugs, including ketoconazole and itraconazole (Sporanox, Tolsura). But doxycycline isn’t known to interact with Viagra.

Will modafinil interact with Viagra if I take them together?

No, modafinil (Provigil) should not interact with Viagra if these medications are taken together.

Modafinil is prescribed to treat narcolepsy, sleep apnea, and shift work sleep disorder. There have been no reports of an interaction between Viagra and modafinil. If you have questions about Viagra, modafinil, and interactions, talk with your pharmacist or doctor.

Taking certain steps can help you avoid interactions with Viagra. Before starting treatment, talk with your doctor and pharmacist. Things to discuss with them include:

  • Whether you drink alcohol or use cannabis.
  • Other medications you take, as well as any vitamins, supplements, and herbs. Your doctor or pharmacist can help you fill out a medication list.
  • What to do if you start taking a new drug during Viagra treatment.

It’s also important to read Viagra’s label and other paperwork that comes with the drug. You may see colored stickers on the label that describe interactions. And the paperwork (sometimes called the prescribing information) may have other details about interactions. If you need help understanding this information, talk with your doctor or pharmacist.

Taking Viagra exactly as prescribed can also help prevent interactions.

If you still have questions about Viagra and its possible interactions, talk with your doctor.

Questions you may want to ask your doctor include:

  • Will my Viagra dosage affect my risk of interactions?
  • Should I avoid taking Viagra at the same time as my other medications?
  • Do other drugs that could treat my condition have similar interactions as Viagra?

While taking Viagra, do not start taking new medications or supplements without first talking with your doctor or pharmacist. Some interactions with Viagra can be dangerous or even life threatening. Your pharmacist or doctor can check any new medications or supplements for interactions with Viagra.

Disclaimer: Healinggeeks has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.