Viagra (sildenafil) is a brand-name prescription drug used to treat erectile dysfunction. As with other medications, Viagra can interact with certain other drugs and foods. However, Viagra is not known to interact with alcohol or supplements. An interaction occurs when one substance causes another substance to have a different effect than expected.

For details about Viagra’s interactions, keep reading. For additional information about Viagra, see this article.

In some cases, a factor or condition could prevent your doctor from prescribing Viagra due to the risk of harm. This is known as a contraindication. The contraindications of Viagra include the ones mentioned below.

Note: Before you start treatment with Viagra, it’s important to tell your doctor if these contraindications apply to you. They can determine whether to prescribe the medication.

Taking a nitrate

Doctors typically will not prescribe Viagra with nitrates. These are medications used to treat or help prevent angina (a type of chest pain). Nitrates also include a group of illicit drugs called poppers, such as amyl nitrate.

Nitrates can lower blood pressure. Taking Viagra with nitrates may lower blood pressure further. A sudden drop in blood pressure can lead to dizziness and fainting. In severe cases, it may lead to stroke or heart attack.

Below are examples of nitrates that can interact with Viagra:

  • nitroglycerin (Nitro-Dur, Nitromist, Nitrostat)
  • isosorbide dinitrate (Isordil)
  • isosorbide mononitrate (Monoket)

If you take a nitrate, talk with your doctor before taking Viagra. They can recommend a different treatment option for your condition.

Taking a guanylate cyclase stimulator

Doctors typically will not prescribe Viagra with guanylate cyclase (GC) stimulators. These are medications used to treat pulmonary arterial hypertension, which is high blood pressure in the arteries of the lungs.

Both Viagra and GC stimulators can lower blood pressure. Taking Viagra with a GC stimulator can lower your blood pressure further.

Below are examples of GC stimulators that can interact with Viagra:

  • riociguat (Adempas)
  • vericiguat (Verquvo)

If you take a GC stimulator, talk with your doctor before starting Viagra treatment. They’ll likely recommend a drug other than Viagra for your condition.

Having had an allergic reaction to Viagra or any of its ingredients

If you have 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.

There’s no known interaction between Viagra and alcohol.

However, drinking alcohol while taking Viagra could worsen some of the drug’s side effects. Examples include flushing, nausea, and dizziness. (For details about possible side effects of Viagra, see this article.)

In addition, drinking large amounts of alcohol can lead to sexual side effects. This includes erectile dysfunction, which Viagra is used to treat. Consuming large amounts of alcohol while taking Viagra could make it hard to tell whether Viagra is working to treat your condition.

If you drink alcohol, talk with your doctor before taking Viagra. They can advise you on whether you should limit your alcohol consumption during your treatment.

Before you start treatment with Viagra, tell your doctor and pharmacist which prescription, over-the-counter, and other medications you take. By sharing this information with them, you may help prevent possible interactions.

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

Here’s a chart of drugs that can interact with Viagra. Due to the risk of interactions, doctors may not prescribe Viagra with these medications. Keep in mind that this chart does not include all drugs that may interact with Viagra. Some of these interactions are described in detail just below in “Drug interactions in depth.”

Drug group or drug nameDrug examplesInteraction result with Viagra
nitrates*nitroglycerin (Nitro-Dur, Nitromist, Nitrostat)
• isosorbide dinitrate (Isordil)
• isosorbide mononitrate (Monoket)
can increase the effect of nitrates
guanylate cyclase (GC) stimulators*• riociguat (Adempas)
• vericiguat (Verquvo)
can increase the effect of GC stimulators
blood pressure drugs• alpha-blockers, such as prazosin (Minipress)
calcium channel blockers, such as amlodipine (Norliqva, Norvasc)
angiotensin receptor blockers, such as losartan (Cozaar)
• central agonists, such as clonidine (Catapres-TTS, Duraclon, Kapvay)
can increase the effect of blood pressure drugs
PDE5 inhibitors• avanafil (Stendra)
tadalafil (Cialis, Adcirca, Alyq)
• vardenafil (Staxyn)
can increase the risk of side effects from Viagra†
certain antifungal drugs• ketoconazole
• itraconazole (Sporanox, Tolsura)
can increase the risk of side effects from Viagra†
erythromycin (E.E.S., Ery-Tab, EryPed, others)can increase the risk of side effects from Viagra†
ritonavir (Norvir)can increase the risk of side effects from Viagra†

* For details about this interaction, see “When to avoid Viagra” above.
† To learn about possible side effects of Viagra, see
this article.

Here’s a closer look at certain drug interactions of Viagra.

PDE5 inhibitors

Drugs called phosphodiesterase 5 (PDE5) inhibitors are used to treat conditions such as erectile dysfunction and pulmonary arterial hypertension.

Interaction result. Taking Viagra with a PDE5 inhibitor can increase the risk of low blood pressure with Viagra.

Interaction explained. Viagra belongs to a drug class called PDE5 inhibitors. Viagra and other PDE5 inhibitors can lower blood pressure when taken on their own. Therefore, taking Viagra with other medications from this same drug class can increase the risk of low blood pressure even more.

Examples of PDE5 inhibitors. Below are PDE5 inhibitors that may interact with Viagra:

Steps you or your doctor may take. Before taking Viagra, be sure to tell your doctor if you’re already taking a PDE5 inhibitor. They’ll likely prescribe a drug other than Viagra for your condition.

Blood pressure drugs

Blood pressure drugs are used to lower blood pressure. Many different classes of blood pressure drugs can interact with Viagra. Examples include:

Interaction result. Taking Viagra with a blood pressure drug can make low blood pressure more likely to occur than usual.

Interaction explained. Both Viagra and blood pressure medications can lower blood pressure when taken on their own. Taking Viagra in combination with blood pressure medication can increase the risk of low blood pressure even more.

Examples of blood pressure drugs. Below are examples of blood pressure medications that may interact with Viagra:

  • alpha-blockers,* such as prazosin (Minipress)
  • CCBs, such as amlodipine (Norliqva, Norvasc)
  • ARBs, such as losartan (Cozaar)
  • ACE inhibitors, such as lisinopril (Zestril)
  • beta-blockers, such as metoprolol (Lopressor, Toprol XL)
  • central agonists, such as clonidine (Catapres-TTS, Duraclon, Kapvay, others)

Steps you or your doctor may take. Before starting treatment with Viagra, it’s important to tell your doctor whether you’re taking any blood pressure medications. They can advise you on whether it’s safe for you to take Viagra. In some cases, they may prescribe a lower starting dose of Viagra. (For details about Viagra’s dosage, see this article.)

* Other alpha-blockers that are not used to treat high blood pressure can also interact with Viagra. An example is tamsulosin (Flomax), which is used to treat benign prostatic hyperplasia.

Certain antifungal drugs

Antifungal drugs are used to treat infections caused by fungi.

Interaction result. Taking Viagra with certain antifungal drugs can increase the risk of side effects of Viagra. (To learn about possible side effects of Viagra, see this article.)

Interaction explained. Certain antifungal drugs can prevent your body from breaking down Viagra. This can lead to a higher level of the drug in your body than usual, which could increase your risk of side effects from Viagra.

Examples of antifungal drugs. Antifungal drugs that may interact with Viagra include ketoconazole and itraconazole (Sporanox, Tolsura).

Steps you or your doctor may take. Before you take Viagra, be sure your doctor knows whether you’re taking any antifungal drugs. They can advise you on whether it’s safe for you to take Viagra with these medications.

Viagra may have other interactions, such as with supplements, foods, vaccines, or even lab tests. You’ll find details below.

Viagra and supplements

As with other medications, drugs can interact with supplements, such as vitamins and herbs.

Viagra and herbs

There were no specific reports of herbs interacting with Viagra. However, it’s still important to talk with your doctor or pharmacist before taking any of these products during Viagra treatment.

Viagra and vitamins

Vitamins have not been reported to interact with Viagra. You should still talk with your doctor or pharmacist before taking any vitamins during your Viagra treatment.

Viagra interactions with food

Eating grapefruit or drinking grapefruit juice while taking Viagra could raise the level of Viagra in your body. A higher level of the drug could increase your risk of side effects. (To learn about possible side effects of Viagra, see this article.)

Viagra and vaccines

There are no specific reports of vaccines interacting with Viagra. If you have questions about getting vaccines while taking Viagra, talk with your doctor or pharmacist.

Viagra and lab tests

Lab tests and Viagra have not been reported to interact with each other. For more information about getting certain lab tests during your Viagra treatment, talk with your doctor or pharmacist.

Viagra interaction with cannabis or CBD

Cannabis (marijuana) and cannabis products, such as cannabidiol (CBD), have been reported to interact with Viagra.

The exact effect of cannabis products on Viagra may vary from person to person. Cannabis products may raise the level of Viagra in the body, which could increase your risk of side effects from Viagra. (To learn about possible side effects of Viagra, see this article.)

On the other hand, cannabis products may also decrease the level of Viagra in the body, which could cause the drug to be less effective than usual.

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 and other factors may increase the risk of interactions with Viagra. Before you take Viagra, be sure to talk with your doctor about your health history. Viagra may not be the right treatment option for you if you have certain medical conditions or other factors affecting your health.

Health conditions or factors that might interact with Viagra include:

  • Liver or kidney problems. If you have liver or kidney problems, be sure to tell your doctor before taking Viagra. Examples of these problems include liver failure and kidney failure. Your doctor may prescribe a decreased dose of Viagra. (For details about Viagra’s dosage, see this article.) Or they may prescribe a treatment other than Viagra.
  • Bleeding problems. Viagra may increase the risk of bleeding if you have a bleeding problem, such as hemophilia. Before taking Viagra, tell your doctor whether you have a bleeding problem. They can advise you on whether the drug is safe for you.
  • Blood cancers. Before starting Viagra treatment, tell your doctor if you have a blood cancer, such as multiple myeloma or leukemia. These conditions can increase your risk of priapism (prolonged, painful erection). Your doctor can help determine whether Viagra is a safe treatment option for you.
  • Problems with blood cells. Before taking Viagra, tell your doctor if you have certain problems with blood cells. This includes sickle cell anemia. This condition can increase your risk of priapism. Your doctor can advise you on whether Viagra is right for you.
  • Heart problems or stroke. Viagra is not recommended if you have or have had certain heart problems or stroke. Examples include having had a heart attack or stroke in the past 6 months. Other examples include low or high blood pressure. It’s not known whether Viagra is safe for people with these conditions. If you have a history of these conditions, your doctor may prescribe a treatment other than Viagra.
  • Eye problems. In rare cases, Viagra may cause serious eye problems such as vision loss. If you have certain eye problems, you may have an increased risk of these side effects. Before taking Viagra, tell your doctor if you have problems with your optic nerve or retina. They can advise you on whether it’s safe for you to take Viagra.
  • Peptic ulcers. Viagra may increase the risk of bleeding if you have a peptic ulcer. If you have this condition, talk with your doctor before starting Viagra treatment. They can help determine whether to prescribe Viagra for you.
  • Misshaped penis. Before taking Viagra, tell your doctor if you have a condition that affects the shape of your penis. Examples include having Peyronie’s disease and a bent penis. These conditions can increase your risk of priapism as a side effect. Your doctor can advise you on whether Viagra is a safe treatment option.
  • Pregnancy. Viagra is not approved for use in females.* It’s not known whether the drug is safe to take during pregnancy. For details about Viagra and pregnancy, see this article.
  • Breastfeeding. Viagra is not approved for use in females.* The drug may pass into breast milk. However, it’s unknown whether this could lead to side effects in a breastfed child. To learn more about Viagra and breastfeeding, see this article.
  • 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.

* Sex and gender exist on spectrums. Use of the term “female” in this article refers to sex assigned at birth.

Here are some frequently asked questions about Viagra and possible interactions.

Do Viagra and ashwagandha interact?

There’s not a known interaction between Viagra and ashwagandha.

Ashwagandha is an herb that some people think eases symptoms of various health conditions, including anxiety, stress, and arthritis.

Ashwagandha is also sometimes used to treat erectile dysfunction (ED). However, it’s unknown whether this herb is effective for treating ED.

To learn more about Viagra and ashwagandha, talk with your doctor or pharmacist. They can advise you on whether it’s safe to take ashwagandha during Viagra treatment.

Does Viagra interact with statin drugs?

Viagra is not known to interact with statin drugs. Statins are used to treat high cholesterol. Examples include Lipitor (atorvastatin) and Zocor (simvastatin).

Having high cholesterol may increase your risk of ED, which Viagra is used to treat. If you have ED related to high cholesterol, your doctor may prescribe Viagra to treat your condition.

You can talk with your doctor or pharmacist if you have questions about statins and Viagra.

Is there an interaction between Viagra and omeprazole?

There’s no known interaction between Viagra and Prilosec (omeprazole). The drug omeprazole is used to treat certain digestive problems, such as heartburn.

There has been at last one report of omeprazole causing ED. (Viagra is prescribed for this condition). If you have ED due to omeprazole, your doctor can advise you on the right treatment option for you. This may include taking Viagra.

Can I take Viagra with allergy or cold medication, such as Claritin or Sudafed?

Neither Claritin (loratadine) nor Sudafed (pseudoephedrine) have been reported to interact with Viagra.

Claritin is a type of medication called an antihistamine and is used to treat conditions such as seasonal allergies. Sudafed is a type of drug called a decongestant and is used for conditions such as nasal congestion.

If you are interested treating allergies or a cold while taking Viagra, talk with your doctor or pharmacist.

Does Viagra interact with blood thinners, such as warfarin or Xarelto?

There’s no known interaction between Viagra and blood thinners, such as warfarin or Xarelto (rivaroxaban). Warfarin and Xarelto are used to treat or help prevent conditions such as blood clots in the body.

If you’d like to learn more about Viagra and blood thinners, talk with your doctor.

You can take certain steps to help prevent interactions with Viagra. Your doctor and pharmacist are key resources, so reach out to them before starting treatment. For example, you should plan the following:

It’s also important to read the label of Viagra and other paperwork that comes with the drug. The label may have colored stickers that mention an interaction. And the paperwork, sometimes called the prescribing information, may contain details about interactions. If this information is difficult to understand, ask your doctor or pharmacist to help explain it.

You can also help prevent interactions with Viagra by taking it exactly as your doctor prescribes.

Besides learning about interactions, you may want to find out more about Viagra. These resources might help:

Disclaimer: Medical News Today 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.