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Blue Rx pill: Sildenafil interactions to avoid
Drug Info

Sildenafil interactions to avoid

Sildenafil interacts with nitrates, alpha-blockers, and medications that treat high blood pressure
Karen Berger medical writer and reviewer headshot
By | Jan. 18, 2024

Key takeaways

  • Sildenafil can treat erectile dysfunction or pulmonary arterial hypertension, depending on the formulation.

  • Some interactions to be aware of include nitrates, alpha-blockers, and medications that treat high blood pressure.

  • Always tell your healthcare provider about your medications, including prescription and OTC drugs, vitamins, and supplements.

Drug interactions | Food interactions | Other interactions | Avoiding interactions | When to talk to a doctor

Sildenafil is a generic prescription drug commonly known by the brand names Viagra and Revatio. Viagra is available in 25 mg, 50 mg, and 100 mg tablets. Viagra and generic sildenafil in these strengths are approved by the U.S. Food and Drug Administration (FDA) to treat erectile dysfunction (ED). Revatio is available in 20 mg tablets. Revatio and generic sildenafil in this strength are FDA-approved to treat pulmonary arterial hypertension (PAH). PAH is a condition of high lung blood pressure caused by obstruction of the small arteries. 

Sildenafil is a member of a drug class known as phosphodiesterase-5 (PDE5) inhibitors. For erectile dysfunction, sildenafil works by increasing blood flow to the penis in combination with sexual stimulation. This helps cause an erection. For PAH, sildenafil works by relaxing blood vessels in the lungs, which helps blood flow.

Sildenafil is a commonly prescribed medication. As of 2020, in the United States, over one million people filled almost 3 million prescriptions for this drug. When taking sildenafil, it is important to be aware of various drug interactions and other factors, such as certain foods, that can cause or worsen adverse effects or affect how effective this medicine is. Continue reading to learn more about sildenafil interactions. 

Sildenafil-drug interactions

Whether you take sildenafil for ED or PAH, the interactions are the same. Let’s review some of the drug interactions of sildenafil.

Nitrates

Nitrates are a class of medications used to treat certain cardiovascular conditions, such as chest pain (angina). They are known as vasodilators because they dilate the veins and arteries, which helps improve chest pain. However, nitrates also have a hypotensive effect, lowering blood pressure. Sildenafil should never be taken with any nitrate medications because it makes the hypotensive effect stronger and could cause dangerously low blood pressure and fainting. Healthcare providers will never prescribe sildenafil to someone who takes a nitrate medication. Examples of nitrates include:

This also includes illicit drugs called “poppers,” such as amyl nitrate, amyl nitrite, or butyl nitrate. 

Alpha-blockers

Alpha-blockers are a class of medications used to treat high blood pressure or an enlarged prostate (benign prostatic hyperplasia, or BPH). The prescribing information for sildenafil warns that combining it with an alpha-blocker may result in increased effects on lowering blood pressure. If the healthcare provider decides to prescribe this combination of drugs, the patient must be considered stable on an alpha blocker before sildenafil is started at the lowest dose. Examples of alpha-blockers include:

Medications that treat high blood pressure

Because of sildenafil’s vasodilatory actions can have an additive effect with other medications used to treat high blood pressure. This could result in dangerously low blood pressure. If you take medication for high blood pressure, consult your healthcare provider for professional medical advice before taking sildenafil. Many medications treat high blood pressure. Some examples include but are not limited to:

Enzyme inhibitors

Many drugs, including sildenafil, are processed in the body by an enzyme called cytochrome P450 3A4 (CYP3A4). Certain drugs inhibit CYP3A4, slowing the processing of sildenafil. This results in a higher level of sildenafil in the body, which could lead to worsened or more serious side effects, including headache, indigestion, flushing, nosebleeds, dizziness, muscle pain, insomnia, vision or hearing loss, and low blood pressure.

The prescribing information for Revatio (for PAH) recommends that CYP3A4 inhibitors should not be used while taking Revatio. 

The prescribing information for Viagra (for ED) recommends using a low dose of sildenafil if a strong CYP3A4 inhibitor must be taken. Always consult your healthcare provider for medical advice because every individual is different.

In some cases, it may be safer to avoid a CYP3A4 inhibitor altogether. Examples of CYP3A4 inhibitor drugs include:

  • Certain antifungal medicines like Nizoral (ketoconazole) or Sporanox (itraconazole)
  • Macrolide antibiotics such as Biaxin (clarithromycin) or erythromycin
  • Antivirals such as Norvir (ritonavir) and other drugs that contain ritonavir (People who take ritonavir should not take more than one 25 mg dose of sildenafil in 48 hours)

Enzyme inducers

While the enzyme inhibitors mentioned above slow sildenafil processing, enzyme inducers have the opposite effect. They speed up how fast sildenafil is processed in the body. This means that sildenafil may be less effective, and a higher dose may be required. The patient will be monitored carefully if an enzyme inducer is combined with sildenafil. In some cases, the healthcare provider may recommend a different medication. Examples of these enzyme inducers include:

Guanylate cyclase stimulators

Adempas (riociguat) and Verquvo (vericiguat) are part of a drug class called guanylate cyclase stimulators. Adempas is used to treat pulmonary arterial hypertension, and Verquvo is used to treat heart problems such as congestive heart failure. Neither of these drugs can be taken with sildenafil. Combining one of these drugs with sildenafil can cause additive effects on lowering blood pressure. 

Other sildenafil products

People who take sildenafil should not take more than one sildenafil product. For example, someone who takes sildenafil for PAH would not be prescribed Viagra (sildenafil)—or any other PDE5 inhibitor such as Cialis (tadalafil) or Levitra (vardenafil)—for erectile dysfunction. 

Sildenafil-food interactions

Sildenafil and high-fat foods

You can take sildenafil with or without food. However, if you take sildenafil after a meal high in fat (for example, pizza and ice cream), the medicine may take longer to begin working. 

Sildenafil and grapefruit 

Grapefruit, as well as grapefruit juice products (including any type of mixed fruit juice that contains grapefruit), acts as an enzyme inhibitor, which may increase sildenafil levels in the body. Ask your healthcare provider how much, if any, grapefruit you can consume while taking sildenafil.

Other sildenafil interactions

In addition to the interactions noted above, there are some other sildenafil interactions to be aware of. 

Sildenafil and alcohol

While sildenafil and alcohol do not have a defined chemical interaction, it is best to avoid alcohol while taking sildenafil for several reasons. Excessive alcohol consumption is linked to sexual issues, particularly when using sildenafil for erectile dysfunction (ED). Combining alcohol with sildenafil may exacerbate a decrease in sexual activity, according to studies. Also, when drinking alcohol, blood pressure can initially drop (and later increase). Since sildenafil can lower blood pressure, this combination could cause dangerously low blood pressure. It’s best to ask your healthcare provider how much, if any, is a safe amount of alcohol to consume while taking sildenafil.

Sildenafil and allergies/medical conditions

People who have had an allergic reaction to sildenafil (symptoms include hives, difficulty breathing, and swelling of the face, lips, tongue, or throat) should never take sildenafil in the form of Viagra or Revatio.

There are also certain health conditions where the healthcare provider will weigh the benefits vs risks of prescribing sildenafil. If the medication is prescribed, the patient will be closely monitored. Examples include:

  • Patients with anatomical problems with the penis, such as Peyronie’s disease
  • People with a medical condition that increases the chance of priapism (a prolonged, painful erection, which is a medical emergency), such as sickle cell anemia, multiple myeloma, or leukemia
  • People with heart disease, heart rhythm conditions, or recent heart attack or stroke
  • People with bleeding conditions
  • People with peptic ulcer disease
  • People with kidney or liver problems
  • People who take medicine (or more than one medicine) to treat high blood pressure
  • People with certain eye conditions like retinitis pigmentosa

Sildenafil and illicit drugs

As mentioned above, sildenafil should never be taken with any type of nitrate. In addition to prescription nitrate medications, this also includes illicit drugs called “poppers,” such as amyl nitrate, amyl nitrite, or butyl nitrate. Although these drugs are not legal and cannot be found in any pharmacy, it is worth noting that they contain nitrates and should never be combined with sildenafil.

How to minimize sildenafil interactions

Sildenafil has some potential interactions, but in many cases can still be taken safely with some precautions. 

Always talk to your healthcare provider before starting a new medication. Before taking sildenafil, be sure your provider knows your medical conditions and history. Also, tell your doctor about any allergies to medicine and all your medications, including prescription and OTC drugs, vitamins, and dietary supplements. While taking sildenafil, do not start any new medication unless your healthcare provider tells you it is safe.

Your healthcare professional may need to adjust the dosage or even change your medication in case of a possible interaction. While taking sildenafil, be aware of potential warning signs of drug interactions, such as feeling dizzy or lightheaded. Always take your medication as directed by your healthcare provider, and ask your provider if you have any questions or concerns about your medications. 

When to talk to a healthcare provider about sildenafil interactions

This article lists various drug interactions but is not a complete list of all possible sildenafil interactions. It is important to tell your healthcare providers about your medications (including prescription medications, over-the-counter drugs, vitamins, and supplements) and your medical conditions to ensure proper management and monitoring. Also, while taking sildenafil, you should not start any new medication unless approved by your healthcare provider.

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