Highlights
- Viagra works like a blood pressure drug and can interact with hundreds of other medications.
- It is important to know which drugs interact with Viagra and how.
- Some interactions can result in life-threatening side effects.
- Always tell your doctor what other medications you take before taking Viagra or sildenafil (generic Viagra).
Sildenafil citrate, the active substance in Viagra, is a PDE-5 inhibitor that relaxes the smooth muscles of the arteries. It works like some blood pressure medications. If you take it with another drug that affects your blood pressure, you may experience dangerous side effects. Find out which drugs interact with Viagra and how.
Which Drugs Interact With Viagra?
Most drugs interact with other drugs in one way or another. Many also interact with over-the-counter medications, vitamins, and supplements you may take without a prescription. Some foods may also affect how your drug works.
Some drug interactions are dangerous, leading to potentially life-threatening side effects. Others are mild. Doctors know about many drug interactions, but new ones can always happen.
Major Viagra Drug Interactions
In addition to blood pressure medications, drugs that affect the levels of liver enzymes and some foods can also cause severe interactions with Viagra.
Nitrates
Nitrates are drugs that doctors prescribe for chest pain and other heart conditions, such as nitroglycerin and many others. Like Viagra, nitrates work by dilating the blood vessels. Patients who take both drugs risk compounding their effects. The blood vessel-dilating effects of the combination are so intense that they can lead to a dangerous drop in blood pressure.
Alpha Blockers
Like Viagra, alpha-blockers work on the smooth muscles of blood vessels. Although they work through different means, both medications reduce blood pressure. Using them together can lead to dangerously low blood pressure.
Though there are many alpha-blockers, two are of particular interest to men who take erectile dysfunction medication:
- Doxazosin. Doctors may prescribe this drug to treat high blood pressure and benign prostatic hyperplasia (BPH), also known as prostate enlargement. Prostate enlargement often goes hand-in-hand with erectile problems, and people with ED are more likely to take Viagra. If you are taking doxazosin, talk to your doctor before using Viagra.
- Tamsulosin. This medication is also used to treat BPH, often in combination with tadalafil (Cialis)— for better BPH management. Tansulosin doesn’t affect blood pressure as much as some of the other drugs in this class of medications (including doxazosin), but the combination may still produce dangerous interactions. If you’re taking tamsulosin in combination with tadalafil, do not take with Viagra.
CYP3A4 inhibitors
CYP3A4 is an enzyme that plays a key role in the metabolism of numerous medications, including sildenafil. Certain drugs, known as CYP3A4 inhibitors, can slow down the activity of this enzyme and increase levels of sildenafil in the blood.
Antiretroviral medications like atazanavir, ritonavir, and saquinavir are examples of CYP3A4 inhibitors. These drugs are primarily used to manage HIV and can elevate sildenafil concentrations in the bloodstream, increasing the risk of adverse effects.
The class of CYP3A4 inhibitors is not limited to antiretrovirals; it also includes antifungal medications such as ketoconazole and certain antibiotics, like erythromycin.
While not all drugs in this class will have the same degree of interaction, tell your doctor if you take a CYP3A4 inhibitor. Doctors may be able to adjust your medications to compensate for the side effects CYP3A4 inhibitors can cause.
Other ED Medications
Like Viagra, other phosphodiesterase-5 inhibitors — vardenafil (Levitra and Staxyn), tadalafil (Cialis), and avanafil (Stendra) — work by relaxing and dilating the blood vessels. Taking these drugs with Viagra or sildenafil compounds their effects and can cause dangerously low blood pressure.
Never take two ED medications (such as Viagra and Cialis) simultaneously without a doctor’s supervision.
Medications That Affect Liver Enzymes
Many medications, such as ketoconazole, can increase the levels of many different drugs in the bloodstream, including Viagra. Over-the-counter medications like acetaminophen (Tylenol) can also affect liver function. Sildenafil can raise liver enzymes in a small number of people. It rarely causes severe liver damage, but it may compound the hepatotoxic effects of other medications.
See Drugs.com’s Drug Interaction Checker for more information about all of sildenafil’s 37 major drug interactions.
Amyl Nitrite
Amyl nitrite is technically a nitrite rather than a nitrate, but its effect on blood pressure is the same. This medication is an inhaler used to treat chest pain, or angina. Amyl nitrite is often used recreationally as “poppers,” and the practice can be life-threatening for men who are already taking blood pressure or erectile dysfunction medication.
Grapefruit
While not a drug, grapefruit or grapefruit juice can also be dangerous when taken with Viagra. Grapefruit boosts sildenafil levels in the blood, which can cause side effects like headaches, flushing, and hypotension. You should not consume grapefruit when taking Viagra or sildenafil.
Moderate Viagra Drug Interactions
285 drugs can interact with Viagra moderately, covering a wide range of drug classes, including:
- Anticoagulants. Drugs that prevent blood clotting, like warfarin (Coumadin) can cause patients to bleed easily when combined with sildenafil.
- Anti-tumor drugs. Medications like brigatinib (Alunbrig) can reduce sildenafil levels in the blood. Tyrosine kinase inhibitors may cause your “magic pill” to lose its “magic.”
- Narcotics. Opioids like codeine and fentanyl may enhance Viagra’s effects and duration. Combining these drugs with Viagra may lead to priapism — long-lasting, painful erections that require medical attention.
- Immunosuppressants. Drugs like cyclosporine that suppress the immune system can increase sildenafil levels in the blood and cause priapism.
- Prostaglandins. Prostaglandins, like epoprostenol, cover a wide range of medications that act like natural hormones in the body. They are prescribed for a number of reasons, including inflammation and pain. Sildenafil may enhance the effects of these medications, causing low blood pressure.
- ACE inhibitors. These are commonly prescribed blood pressure medications, like lisinopril (Zestril) and benazepril (Lotensin). Taken together with sildenafil, they can cause dangerously low blood pressure.
- Minoxidil. This hair loss drug is another medication that works by improving blood circulation and lowering blood pressure. Patients who take it with sildenafil may experience a dangerous drop in their blood pressure.
Because of the large number of medications that can cause moderate side effects, be sure your provider knows of all the medications you’re taking before you take Viagra.
Minor Sildenafil Drug Interactions
We only know about a handful of drugs that can interact mildly with Viagra or sildenafil.
- Modafinil. This alertness-inducing drug increases the heart rate and blood pressure. Its effects may cancel those of sildenafil, making it less effective.
- Theophylline. This medication relaxes the muscles around the airways to improve blood flow and breathing. Smoking reduces theophylline levels in the blood, which may reduce the effects of Viagra. Caffeine increases theophylline levels, which may enhance the effects of Viagra.
- Dipyridamole. Dipyridamole is an antiplatelet agent that thins the blood, which can cause easy bleeding when taken with Viagra.
Viagra Warnings and Precautions
FDA Prescribing Information for Viagra lists the following precautions:
- Sexual activity. Doctors don’t recommend sexual activity to some patients with cardiovascular problems. These patients should avoid taking Viagra. Some sildenafil side effects can be life-threatening for them.
- Priapism. When interacting with other drugs, Viagra can cause long-lasting erections exceeding four hours. Those who experience this side effect should seek medical attention as soon as possible.
- Vision loss. Extremely rarely, Viagra can cause vision loss in one or both eyes. If you experience this problem, stop using the drug immediately and see your doctor.
- Hearing loss. Stop taking Viagra if you lose your hearing and see your doctor.
Be sure your providers have updated medication lists, and include all the over-the-counter medications and supplements you take.
What to Do if You Have an Adverse Reaction to Viagra?
If you have an adverse reaction while taking Viagra, your first step is to stop taking the drug. Depending on the severity of your symptoms, you should seek medical attention or wait for Viagra to clear your system.
Seek medical help immediately if you experience:
- Chest pain that spreads to your arms and/or jaw
- Irregular heartbeat
- Vision or hearing loss
- Swelling in the extremities
- Lightheadedness
- Seizures
- Trouble breathing
Sildenafil’s more common side effects include:
- Headaches
- Back pain
- Nausea
- Bleeding or stuffy nose
- Dizziness
- Flushing
- Heartburn
- Mild vision changes
Most common side effects are Viagra are not serious, and many will resolve as your body clears the Viagra from your system.
Conclusion
While the list of potential drug interactions with Viagra is long, it’s important to note that serious interactions with Viagra are rare, and many side effects are temporary. Viagra has a long record of being safe for most men to take. However, drug interactions vary from one individual to another, so be mindful of any new symptoms when you begin taking any new medication.
If you have any concerns about new or unusual symptoms after taking Viagra or sildenafil, talk to your healthcare provider. Some interactions may be resolved by adjusting your dose or switching to another ED medication.
For a complete look at all of Viagra’s side effects, read our Comprehensive Guide to Viagra and Sildenafil Side Effects | Online Prescription Medications.
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James spent the better part of the last decade studying and writing about the physiology of sleep and its correlations with dreams. He studied various drugs, natural substances, and hallucinogens that can impact the intensity and frequency of dreams.
For two years, he busted dietary supplement scams, analyzing various performance-enhancing compounds, nootropics, etc.
