The Wellness Collective

What to Know About Sildenafil

Mariah Powers
February 5, 2026

Reviewed by Ashley Robinson, PharmD, Pharmacy Manager for TelyRx

Sildenafil is one of the most widely recognized prescription medications in the world, best known by its brand name, Viagra. It is FDA-approved to treat erectile dysfunction (ED) in men.

Sildenafil is famous for being the first oral pill approved for ED. It is a “demand” medication, meaning you take it shortly before you plan to have sex, rather than every day. While typically prescribed as 25 mg, 50 mg, or 100 mg tablets for ED, it is also sold under the brand name Revatio (in 20 mg tablets) to treat pulmonary arterial hypertension (high blood pressure in the lungs).

How Does Sildenafil Work?

Sildenafil is a phosphodiesterase type 5 (PDE-5) inhibitor.

During sexual arousal, your body releases nitric oxide, which triggers a chemical chain reaction to relax the smooth muscles in the penis and fill it with blood. Sildenafil protects the chemical responsible for this relaxation (cGMP) from being broken down by the enzyme PDE-5. This allows the blood vessels to stay open longer and wider, helping you get and keep an erection.

Note: It does not create an erection on its own; sexual stimulation is still required.

Drug Facts

Common Brands	Viagra, Revatio
Drug Class	Phosphodiesterase-5 (PDE-5) inhibitor
Generic Status	Generic version of Viagra
Availability	Prescription Only

Dosing

Note: Dosing information below is educational only. Your prescribing physician will determine your specific dose based on your individual health needs.

Sildenafil is taken “as needed.” It is not a once-daily pill. The typical starting dose is 50 mg. It is best taken approximately 1 hour before sexual activity. However, it can be taken anywhere from 30 minutes to 4 hours before.

Based on effectiveness and side effects, your doctor may increase the dose to a maximum of 100 mg. A lower starting dose of 25 mg is often recommended for men aged 65 and older, or those with kidney or liver impairment, to reduce the risk of side effects.

Do not take sildenafil more than once per 24 hours.

Always follow your healthcare provider’s instructions for exact dosing.

FDA-Approved Uses

Erectile Dysfunction (ED) – To treat the inability to get or keep an erection sufficient for sexual performance.
Pulmonary Arterial Hypertension (PAH) – Sold under the brand Revatio (usually 20 mg), it is used to relax blood vessels in the lungs to lower blood pressure and improve exercise capacity.

Common Off-Label Uses

You may see sildenafil prescribed for uses that are not “FDA-approved.” This is a very common and legal practice called “off-label” prescribing, where a doctor uses their clinical judgment to prescribe a drug for a different (but well-researched) purpose.

While primarily used for ED and PAH, healthcare providers sometimes prescribe sildenafil off-label for other conditions involving blood flow:

Raynaud’s Phenomenon – To help improve severe circulation issues in the fingers and toes caused by cold or stress.
High-Altitude Pulmonary Edema (HAPE) – It is sometimes used by mountain climbers to prevent or treat fluid buildup in the lungs at high altitudes.

Side Effects

Most side effects are mild to moderate and tend to fade as the drug leaves your system (usually within 4-6 hours).

Common Side Effects

Headache
Flushing (warmth or redness in the face/neck)
Indigestion or upset stomach
Nasal congestion (stuffy nose)
Vision changes, such as seeing a blue tinge to objects, difficulty telling blue from green, or sensitivity to light.
Dizziness

Serious Side Effects

Serious side effects are rare, but it’s important to know what to look for if they do occur. Stop taking sildenafil and seek emergency medical help if you experience:

Priapism – An erection that is painful or lasts longer than 4 hours. This is a medical emergency that can cause permanent damage to the penis if not treated immediately.
Sudden Vision Loss – Sudden loss of vision in one or both eyes (NAION).
Sudden Hearing Loss – Sudden decrease or loss of hearing, often accompanied by ringing in the ears.
Severe Low Blood Pressure – Dizziness, fainting, or lightheadedness.
Cardiovascular Symptoms – Chest pain, pressure, or severe shortness of breath during sexual activity.
Allergic Reaction – Hives, difficulty breathing, or swelling of the face/throat.

Call your doctor immediately if you experience any concerning or prolonged symptoms.

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Sildenafil is a medication used to treat erectile dysfunction. Dosing depends on age, tolerance, and response to the medication.

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Pharmacist Tips

Watch Your Meal – While you can take sildenafil with food, a high-fat meal (like a cheeseburger or steak) will delay the drug’s absorption. It may take longer to work or be less effective. For the fastest results, take it on an empty stomach.
Do NOT Mix with Nitrates – NEVER combine sildenafil with nitrates (nitroglycerin, isosorbide) or recreational “poppers” (amyl nitrite). This can cause a dangerous, potentially fatal drop in blood pressure.
Stimulation is Needed – The pill does not work like a switch. You still need sexual stimulation and arousal for the medication to work.
Alcohol Caution – Heavy drinking can worsen side effects like dizziness and low blood pressure. Ironically, excessive alcohol also makes it harder to get an erection, counteracting the medication.
Be Patient – It may take a few attempts to find the right timing and dose. Don’t give up if it doesn’t work perfectly the very first time.

Drug Interactions

Sildenafil interacts with several common medications.

DO NOT TAKE SILDENAFIL if you take:

Nitrates (nitroglycerin, isosorbide mononitrate/dinitrate).
Guanylate Cyclase Stimulators (Riociguat for pulmonary hypertension).

Use caution and inform your doctor if you take:

Alpha-blockers (tamsulosin/Flomax) – Used for prostate issues. Taking these together can cause low blood pressure. Your doctor may advise separating the doses by a few hours.
Blood Pressure Medications – Sildenafil adds to the blood-pressure-lowering effect.
Protease Inhibitors (Ritonavir) – Used for HIV.
Antifungals (Ketoconazole).
Grapefruit Juice – Can increase the levels of sildenafil in your blood, potentially worsening side effects.

Always give your doctor and pharmacist a complete list of all your medications, vitamins, and supplements to check for potential interactions.

FAQs

How long does Viagra (sildenafil) last?

Sildenafil typically stays active in your system for 4 to 6 hours. This does not mean you will have an erection for that long, but that you can achieve one during that window with stimulation.

How much sildenafil should I take for the first time?

The standard starting dose is usually 50 mg. However, if you are over 65 or have kidney/liver issues, your doctor will likely start you on 25 mg. Always follow your provider’s instructions.

How long does it take for sildenafil to take effect?

It typically takes 30 to 60 minutes to start working. It works fastest if taken on an empty stomach.

Can I take Viagra every day?

Sildenafil is generally prescribed for use “as needed” before sex, not as a daily scheduled pill. If you require ED treatment daily or want more spontaneity, talk to your doctor about tadalafil (Cialis), which has a specific low-dose “once-daily” option.

Can women take sildenafil?

Sildenafil is not FDA-approved for sexual dysfunction in women. While some studies have looked into it, results are mixed. It is FDA-approved for women only for the treatment of pulmonary arterial hypertension (PAH).

Does sildenafil make you last longer?

No. Sildenafil helps you get and keep an erection. It does not treat premature ejaculation (how fast you climax) or increase your libido (sex drive).

What should I do if sildenafil doesn’t work?

Don’t panic. It is common for it not to work perfectly the first time. It may take a few attempts for your body to adjust. Ensure you waited long enough (1 hour), didn’t eat a heavy meal beforehand, and were sexually stimulated. If it still doesn’t work after several attempts, talk to your doctor about adjusting the dose or trying a different medication like tadalafil.

Can I cut sildenafil pills in half?

Generally, yes. Unlike some extended-release medications, sildenafil tablets can usually be split if they are scored (have a line down the middle). However, it is always best to use the specific strength prescribed to you. Ask your pharmacist if your specific brand of generic sildenafil is safe to split.

Does sildenafil expire?

Yes, like all medications, sildenafil has an expiration date printed on the bottle or pharmacy label. Do not take expired medication, as it may not be effective and could potentially be unsafe.

How does sildenafil compare to tadalafil and vardenafil?

While all three are PDE-5 inhibitors used for ED, they have large differences in duration and food interactions:

Sildenafil (Viagra) – Lasts 4-6 hours. Works best on an empty stomach (high-fat meals delay it). Good for planned sexual activity.
Tadalafil (Cialis) – Lasts up to 36 hours. Can be taken with or without food. Ideal for spontaneity or “weekend” use.
Vardenafil (Levitra) – Lasts 4-6 hours (similar to sildenafil). It is slightly less affected by food than sildenafil and is sometimes effective for men who did not respond well to sildenafil.

Compare Medications

Compared: Sildenafil, Tadalafil, Vardenafil, or Avanafil?

Sildenafil is the original PDE-5 inhibitor, but there are alternatives.

Sildenafil (Viagra) – The “little blue pill.” Works in 30-60 minutes and lasts for 4-6 hours. Best on an empty stomach.
Tadalafil (Cialis) – The “weekend pill.” Lasts up to 36 hours. It can be taken with food and has a daily dosing option.
Vardenafil (Levitra) – Similar duration to sildenafil (4-6 hours) but is very potent and requires smaller doses (mg for mg).
Avanafil (Stendra) – The fastest-acting option, often working in as little as 15 minutes.

Disclaimer

Important: Information on this page is for educational purposes only. Prescribing decisions are made by independent, licensed providers. TelyRx operates technology-enabled pharmacies and a telehealth platform that connects patients with board-certified licensed providers. Prescriptions, when provider-approved and issued, are filled and shipped by TelyRx-affiliated pharmacies. We do not employ physicians or make prescribing decisions. Learn more about our editorial standards here.

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