Viagra

What is Viagra?

Viagra is an oral medication belonging to a class of drugs called phosphodiesterase-5 (PDE5) inhibitors. It blocks the action of a specific enzyme to relax the muscles lining the blood vessels within the penis, which increases blood flow to the area. It works in conjunction with the chemicals released during sexual arousal to help produce and maintain an erection.¹ ² ³

What is Viagra used to treat?

Viagra is approved by the US Food and Drug Administration (FDA) for the treatment of erectile dysfunction (ED) in adult men. While the generic form and other brands of sildenafil are used to treat other health conditions, this article focuses on Viagra in particular.⁴

What You Need To Know About Erectile Dysfunction

Dosage forms and strengths

Viagra is available as an oral tablet in the following strengths:⁵

• 25mg

• 50mg

• 100mg

The typical starting dose for Viagra is one 50mg tablet. However, some patients will need dose adjustments up to 100mg or down to 25mg.⁶

Your doctor will determine the appropriate dose for you depending on your condition, medical history, risk of side effects, and potential medication interactions. Follow your doctor’s recommendations closely when using Viagra. Taking too much Viagra (or taking it too often) can have severe consequences.

How do you take Viagra?

Viagra is taken orally, with or without food, and as needed. The common starting dose of Viagra is 50mg, and it can be increased to 100mg if the response to the initial starting dose is less than expected. Always take the exact amount prescribed by your doctor.⁷

It is usually best to take Viagra about one hour before sexual activity, but it can be effective if taken any time between 30 minutes and four hours before sexual activity. You should take no more than one Viagra dose per 24-hour period.⁸

Seeing results

It takes about 30 minutes for Viagra to start working, and the medication continues to work for about four hours after taking the dose. It is important to remember that sexual stimulation is necessary to trigger an erection. There’s no risk of developing a spontaneous erection in the absence of stimulation.⁹ ¹⁰

Who should not take Viagra?

Viagra is not suitable for people who are allergic to the medication’s active or inactive ingredients. While the drug is commonly prescribed for younger and older men, Viagra should be prescribed cautiously in patients older than 65 years who may need a lower dose.¹¹

Additionally, extra caution is warranted in people with one or more of the following conditions:¹² ¹³

• Chest pain or other conditions requiring treatment with nitrates

• Cardiovascular disease, including chest pain, history of a heart attack or stroke, high blood pressure, heart failure, or heart rhythm abnormalities

• High cholesterol or other heart attack risk factors

• Blood circulation problems

• Pulmonary arterial hypertension

• Liver or kidney disease

• Bleeding or blood clotting disorder

• Sickle cell anemia, multiple myeloma, or leukemia

• Peyronie disease or other conditions affecting the penis

• Eye diseases, such as retinitis pigmentosa or other causes of sudden vision loss

Potential side effects of Viagra

Viagra can trigger side effects ranging from mild to severe. Although serious side effects are rare, knowing the signs can help you understand when to seek medical attention.

Common side effects of Viagra include the following:¹⁴

• Gastrointestinal upset

• Flushing

• Dyspepsia (pain or discomfort in the upper stomach)

• Nasal congestion

• Nosebleed

• Back pain

• Rash

• Feeling lightheaded or dizzy

• Headache

• Muscle aches

• Blurry vision

• Light sensitivity

• Heart palpitations

If these side effects do not improve over time or get worse, speak with your doctor.

If you experience any of the following serious side effects, call 911 or seek emergency care immediately:¹⁵

• Erection lasting longer than four hours

• Painful erection

• Loss of vision

• Loss of hearing

• Severe dizziness or lightheadedness

• Ringing in the ears

• Severe shortness of breath

• Irregular heart rhythm

• Swelling in your hands, ankles, or feet

• Pain in the arm, chest, or jaw

• Seizure

Overdose

It is possible to overdose on Viagra. Symptoms of an overdose are similar to the adverse effects seen in people taking typical doses but are generally more severe. If you believe you’ve taken too much Viagra, contact the National Poison Control helpline or call 911, depending on the severity of your overdose symptoms.¹⁶

Allergy information

It’s rare, but some people are allergic to Viagra. In some cases, people taking Viagra experience an anaphylactic reaction, which is a medical emergency. 

Call 911 if you experience any of the following signs of a drug allergy after taking Viagra:

• Shortness of breath

• Wheezing 

• Rapid heart rate 

• Rash, hives

• Swelling of the mouth, lips, tongue, or throat

• Sudden-onset vomiting 

• Loss of consciousness

Long-term use of Viagra

Viagra is commonly prescribed for long-term use on an as-needed basis. While the medication is generally well-tolerated, some of the men enrolled in a four-year study assessing the drug’s long-term safety and effectiveness reported the following adverse effects:¹⁷

• Heart palpitations

• Stomach pain or discomfort 

• Nasal congestion

• Headache 

In a separate case report, a patient taking sildenafil developed a painful penile blood clot, and his doctors suspect it may have been triggered by long-term Viagra use.¹⁸

Viagra and pregnancy

The US FDA designated Viagra as a pregnancy category B drug. While animal studies did not demonstrate a risk, there are no adequate studies with pregnant women. Usually, a category B drug may be prescribed in cases where the benefits outweigh the potential risks. However, Viagra is not indicated or prescribed for use in women, regardless of pregnancy status.¹⁹

Missed doses

Viagra is taken only when needed. You will take a dose when you expect to engage in sexual activity and no more than once daily. Taking Viagra on a routine or regular basis is not necessary for it to work effectively.²⁰

Drug interactions

Viagra is known to interact with many different medications. Of particular concern are:²¹

• Antibiotics, such as gentamicin, erythromycin, and clarithromycin

• Antifungal medications like ketoconazole (Nizoral) and itraconazole (Sporanox)

• Antiviral drugs, such as atazanavir (Reyataz), fosamprenavir (Lexiva), lopinavir/ritonavir (Kaletra), and others

• Blood pressure drugs: 

  • Alpha-blockers like prazosin (Minipress), doxazosin (Cardura), and alfuzosin (Uroxatral)

  • Angiotensin-converting enzyme (ACE) inhibitors like captopril and benazepril (Lotensin)

  • Beta-blockers like atenolol (Tenormin) and bisoprolol 

  • Nitroprusside 

• Cardiac medications

  • Nitrate derivatives like nitroglycerin (Gonitro) and isosorbide dinitrate 

  • Vericiguat (Verquvo) and riociguat (Adempas)

• Chemotherapy drugs, such as adagrasib (Krazati), ceritinib (Zykadia), and ribociclib (Kisqali)

• Diabetes medications like canagliflozin (Invokana), empagliflozin (Jardiance), and dapagliflozin (Farxiga)

• Diuretics, such as bumetanide and chlorothiazide (Diuril)

• Other forms of sildenafil (such as Revatio)

• Other treatments for ED, such as avanafil (Stendra), tadalafil (Cialis), and vardenafil 

• Alcohol and street drugs, particularly amyl nitrite (“poppers”)

• St. John’s wort

This is not a complete list of drug interactions. Before taking Viagra, speak with your doctor about your current medications and any supplements or other substances you take that could interfere with Viagra or cause harmful consequences.

Can I drink alcohol while taking Viagra?

Drinking alcohol when taking Viagra can affect the drug’s effectiveness, increase its side effects, and cause heart attacks. Speak with your doctor about whether it is safe for you to consume alcohol while taking Viagra.²²

What to discuss with your doctor before starting Viagra

Viagra is available by prescription only, so you’ll need to meet with your doctor before you start taking it. At your appointment, you should discuss the following topics:²³ ²⁴ ²⁵

• Any allergies or previous allergic reactions to sildenafil, Viagra, or other medications

• Your medical history and current medical problems, particularly any history of cardiac disease, circulation problems, heart attack, stroke, abnormal heart rhythm, liver or kidney disease, high or low blood pressure, abnormal penis shape, sickle cell anemia, stomach ulcer, or eye disease

• If you've ever had chest pain with sexual activity or if a doctor has told you to avoid sexual activity for health reasons

• Family history of retinitis pigmentosa

• Depression or other mental health concerns

• Any prescription and over-the-counter drugs, supplements, or herbal preparations you take regularly or occasionally

• Your alcohol, drug, and tobacco use

Stopping Viagra

Since Viagra is taken as needed, you can stop taking it at any time. However, there are reports of psychological dependency development in men who use the drug recreationally (not as a treatment for ED), so if you’ve been using Viagra improperly, speak with your doctor about how to stop safely.²⁶

Drug approval history

• 1998: The US FDA approved Viagra²⁷

Tips for taking Viagra

The following tips can help you take Viagra safely while maximizing the drug’s effectiveness:

• The optimum time to take Viagra is 30–60 minutes before planned sex to help you achieve and maintain an erection during sexual activity.²⁸

• Do not take Viagra with alcohol, as doing so can increase the risk of adverse effects.

• Viagra taken after a high-fat meal may take a little longer to begin working.²⁹

• Never take more of your medication than prescribed.

• Pay close attention to your senses after taking a dose. If, during sexual activity, you begin to feel faint, dizzy, nauseous, or experience chest pain or numbness in your extremities, seek urgent medical care.

• If you experience a painful erection or one lasting longer than four hours, seek immediate medical attention.

Frequently asked questions

How long do the effects of Viagra last?

The duration of its effectiveness depends on various factors, including the dose, the presence of other medical conditions, other medications you’re taking, and your body’s unique handling of the drug. In general, Viagra remains effective for up to four hours, but its effect is significantly milder at four hours than it is at two.³⁰

What does Viagra do the first time you take it?

Viagra begins working after a single dose. You’ll notice the drug’s effects within about 30 minutes of taking it for the first time.