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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
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
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.
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
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
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
Bleeding or blood clotting disorder
Sickle cell anemia, multiple myeloma, or leukemia
Eye diseases, such as retinitis pigmentosa or other causes of sudden vision loss
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
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
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
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
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
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
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
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.
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
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
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
1998: The US FDA approved Viagra²⁷
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.
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
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.
Sources
(As above)
Onset and duration of action of sildenafil for the treatment of erectile dysfunction - PMC
Sildenafil in the treatment of erectile dysfunction: an overview of the clinical evidence - PMC
Sildenafil in the treatment of erectile dysfunction: an overview of the clinical evidence - PMC
Long-term safety and effectiveness of sildenafil citrate in men with erectile dysfunction - PMC
Prolonged oral sildenafil use-induced Mondor disease: a case report
Sildenafil in the treatment of erectile dysfunction: an overview of the clinical evidence - PMC
Viagra: Dosing, contraindications, side effects, and pill pictures - epocrates online
(As above)
Revatio, Viagra (sildenafil) dosing, indications, interactions, adverse effects, and more
(As above)
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Here at HealthMatch, we’ve done our best to ensure that the information provided in this article is helpful, up to date, and, most importantly, accurate.
However, we can’t replace the one-to-one advice of a qualified medical practitioner or outline all of the possible risks associated with this particular drug and your circumstances.
It is therefore important for you to note that the information contained in this article does not constitute professional medical or healthcare advice, diagnosis or recommendation of treatment and is not intended to, nor should be used to, replace professional medical advice. This article may not always be up to date and is not exhaustive of all of the risks and considerations relevant to this particular drug. In no circumstances should this article be relied upon without independent consideration and confirmation by a qualified medical practitioner.
Your doctor will be able to explain all possible uses, dosages, precautions, interactions with other drugs, and other potential adverse effects, and you should always talk to them about any kind of medication you are taking, thinking about taking or wanting to stop taking.
Access the latest treatments and medications. unavailable elsewhere - entirely free of charge. We make it easy to take part.