Drug information Pricing How it works FAQs Learn more

Sildenafil (generic Viagra®)

Sildenafil is a medication that’s used to treat erectile dysfunction (ED). It works by expanding the blood vessels that go to the penis to deliver better blood flow, improving your ability to get and maintain an erection.

Sildenafil citrate is the generic version of Viagra®. The two medications are identical in chemistry and effectiveness. Sildenafil is a cheaper, more widely available option.

Dosage of sildenafil depends on the severity of your ED. Start a free assessment today to receive a personalized care plan to treat your ED.

The following recommendations will help ensure sildenafil works for you:

  • Take it about one hour prior to intercourse
  • Take it on an empty stomach (at least 2 hr after a meal), with a full glass of water and preferably without alcohol. Taking sildenafil immediately after a meal or with alcohol will worsen its absorption and will not allow the medication to work as well.
  • Take it when you will have sexual stimulation. Sildenafil works best when there is sexual stimulation, with or without a partner. It will not work well without stimulation.

Sildenafil can cause mild to moderate side effects, even when taken as directed. Common adverse reactions include:

  • Muscle pain or back pain
  • Flushing, rash, or warm skin on the face, neck, or chest
  • Indigestion, nausea, or diarrhea
  • Headache or tenderness around the eyes
  • Bloody, congested, or runny nose
  • Difficulty sleeping (insomnia)

Occasionally, sildenafil can cause more serious side effects, including:

  • Blurred vision
  • Light sensitivity
  • Decreased color vision or difficulties visually differentiating between colors
  • Buzzing or ringing in the ears
  • Memory problems
  • Confusion
  • Lightheadedness
  • Unusual weakness or exhaustion
  • Difficulty breathing

If you take sildenafil and then experience any of the following:

  • Feeling faint
  • Difficulty breathing
  • Sudden changes in vision, vision loss, or hearing loss
  • Swollen hands, ankles, or feet
  • Chest pain or heart attack symptoms
  • A seizure
  • A painful erection or an erection that lasts more than four hours

you may need immediate medical attention. Call your doctor or go to your nearest emergency room.

Sildenafil is only FDA-approved for erectile dysfunction in men; it is not approved for sexual dysfunction in women. Both male and female patients can take sildenafil to treat pulmonary arterial hypertension.

Sildenafil can cause health complications in people with certain pre-existing conditions and interact poorly with certain medications. So tell your doctor about any current health conditions, prescription medications you take, and over-the-counter medicines, herbal supplements, or street drugs you may use.

You should not take sildenafil with any other drugs or devices meant to encourage erections. Also remember that sildenafil does not protect against HIV/AIDS or sexually transmitted diseases. Always use any precautions to stay safe when engaging in sexual activities.

Sildenafil makes certain drugs less effective, leading to health complications. Nearly 300 medications and street drugs are known to interact with sildenafil, but some combine more poorly than others.

Medications that interact extremely poorly with sildenafil include but are not limited to:

  • Alpha-blockers
  • Amprenavir
  • Amyl nitrate (“poppers”)
  • Atazanavir
  • Boceprevir
  • Ceritinib
  • Clarithromycin
  • Cobicistat
  • Darunavir
  • Delavirdine
  • Erythromycin
  • Fosamprenavir
  • Idelalisib
  • Indinavir
  • Isosorbide
  • Isosorbide dinitrate
  • Isosorbide mononitrate
  • Itraconazole
  • Ketoconazole
  • Lonafarnib
  • Nefazodone
  • Nelfinavir
  • Nitric Oxide
  • Nitroglycerin
  • Nitroprusside
  • Riociguat
  • Ritonavir
  • Saquinavir
  • Telaprevir
  • Telithromycin
  • Troleandomycin
  • Tucatinib
  • Voriconazole

If you take any drugs listed above or any other medication that you worry may interact poorly with sildenafil, talk to your doctor before you stop taking any current medications or start taking new ones.

Talk to a doctor to get your sildenafil prescription today.


Get started

Calculate the price of your sildenafil prescription.


25 mg

Dollar icon36

per month

Save 50%+ compared to other pharmacies


Quantity: 6

K health enlarged logo

Get Sildenafil from K Health for a fraction of the cost.


5 mg



10 mg



20 mg



25 mg



50 mg



100 mg



Price reflects a 10% discount when ordering a 3-month supply.

Personalized ED treatment made simple (and discreet)


Take the

Take the assessment

Answer a few questions about your habits and history to see if treatment from K is right for you.



Select preferences

Let us know your preferred medication, dosage, quantity and delivery schedule.


treatment plan

Review treatment plan

Your personalized treatment plan and prescription info will be shared within 24 hours.


Get your

Get your medication

Your prescription will arrive within two days after approving your treatment plan.

Have any questions?

How much does sildenafil cost?

Sildenafil costs vary from pharmacy to pharmacy. With K Health, you can get a prescription for sildenafil for as low as $36. Plus, we ship the medication straight to you.

How long does sildenafil last?

The effects of sildenafil can last an average of five hours depending on the dosage, condition being treated, and individual taking it. However, if you take sildenafil to treat ED, your erection should not last more than four hours.

How much sildenafil is too much?

Only take the dosage prescribed by your doctor. Taking more than the recommended amount of sildenafil can increase your risk of developing serious side effects.

How long does it take for sildenafil to take effect?

When taken to treat ED, sildenafil typically takes about 30 minutes to an hour to start working. All patients should take sildenafil as directed by their doctor.

Can you buy Viagra or Cialis online?

You can buy Viagra® and Cialis® online if you have a prescription from a doctor. With K Health, you can text with a doctor, get a generic Viagra® or Cialis® prescription, and get your medication shipped directly to your home.

Can you buy tadalafil online?

You can buy tadalafil online if you have a prescription from a doctor. With K Health, you can text with a doctor, get a tadalafil prescription, and get your medication shipped directly to your home.

Can you buy sildenafil online?

You can buy sildenafil online if you have a prescription from a doctor. With K Health, you can text with a doctor, get a sildenafil prescription, and get your medication shipped directly to your home.

Can you buy erectile dysfunction medication online?

Yes, you can buy erectile dysfunction medication online, but you will need a prescription from a doctor to facilitate the purchase. With K Health, you can text with a doctor and get your ED prescription delivered straight to your door.