Sildenafil (Viagra, Revatio): Uses, Dosage, Side Effects and Cost in Canada

Sildenafil is the generic form of Viagra, used for erectile dysfunction. Learn how generic and brand compare, doses, side effects, price in Canada and how to ask a BC doctor.

sexual healthDoctor-reviewedPrescriptionAvailable in Canada
Illustration of a blister card of round tablets for sildenafil (Viagra, Revatio)

Disclaimer: This article is for informational purposes only and does not constitute medical advice. It is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of a physician or other qualified health provider with any questions you may have regarding a medical condition.

Overview

Sildenafil is the medicine in Viagra. It is a prescription tablet for erectile dysfunction (ED), and in Canada it is sold both as brand-name Viagra and as generic sildenafil tablets in 25 mg, 50 mg and 100 mg strengths.

A generic contains the same medicinal ingredient as the brand. Its colour, shape and non-medicinal ingredients can be different, and it is often chosen to lower the cost. Your pharmacist can tell you which products are available.

Sildenafil is also the medicine in Revatio, a separate product used for pulmonary arterial hypertension (high blood pressure in the arteries of the lungs). It has its own dose and is not used for ED. This page is about sildenafil for erectile dysfunction.

Sildenafil needs a prescription. BC residents can speak with a BC-licensed doctor by phone through Avee Health to ask whether it is appropriate for them. The doctor decides based on your health history. A prescription is not guaranteed.

Sildenafil products are used in Canada for two different conditions:

  • Erectile dysfunction in adult men: Viagra and generic sildenafil tablets, taken as needed
  • Pulmonary arterial hypertension: Revatio, a separate product with its own dose, prescribed under specialist care

Sildenafil for ED is not for women or for anyone under 18. It works only with sexual stimulation and does not protect against sexually transmitted infections. The ED tablets and Revatio should not be swapped or taken together.

Generic name

Sildenafil

Drug class

Phosphodiesterase type 5 (PDE5) inhibitor

Category

sexual health

Availability

Prescription required

In Canada

Available

How Sildenafil Works

Sildenafil belongs to a group of medicines called PDE5 inhibitors. Sexual stimulation releases nitric oxide in the penis, which raises the level of a messenger called cGMP. cGMP relaxes smooth muscle so that more blood can flow in. An enzyme called PDE5 breaks cGMP down. Sildenafil blocks that enzyme, which helps the erection response last.

It does not work without sexual stimulation. Blood levels peak about 60 minutes after a dose taken on an empty stomach, and the half-life is 3 to 5 hours.

Dosage Instructions of Sildenafil

Your doctor sets your dose. For erectile dysfunction, the usual directions are the same for brand Viagra and generic sildenafil tablets:

  • Usual dose: 50 mg as needed, about 30 to 60 minutes before sexual activity. It can be taken from 30 minutes to 4 hours before.
  • The dose can be lowered to 25 mg or raised to 100 mg, depending on the response and side effects.
  • Maximum: 100 mg, and no more than one dose a day
  • A 25 mg starting dose is considered at age 65 or older, with liver problems or severe kidney problems, and with alpha-blockers or medicines that raise sildenafil levels. With ritonavir, the maximum is 25 mg in 48 hours.

Swallow tablets whole with water, with or without food. A high-fat meal can delay the effect by about an hour.

Missed dose: for ED, sildenafil is taken only when needed, so there is no missed dose. Do not take more than your prescribed dose or more than one dose a day.

Revatio, the sildenafil product for pulmonary arterial hypertension, has a different dose and schedule set by a specialist. The ED directions above do not apply to it.

Storage Instructions

Store Viagra between 15°C and 30°C in the original package. For generic sildenafil, follow the storage directions on the package or pharmacy label. Keep all tablets out of the reach of children.

Side Effects of Sildenafil

Generic sildenafil has the same medicine as Viagra, so the same side effects apply. In flexible-dose clinical trials, the most common were (sildenafil compared with placebo):

  • Headache: 15.8%, compared with 3.9%
  • Flushing: 10.5%, compared with 0.7%
  • Indigestion: 6.5%, compared with 1.7%
  • Stuffy nose: 4.2%, compared with 1.5%
  • Mild, short-lived vision changes (colour tinge, light sensitivity, blurred vision): 2.7%, compared with 0.4%
  • Dizziness: 2.2%, compared with 1.2%

Get medical help right away if you have:

  • An erection that lasts longer than 4 hours. Delay in treatment can cause permanent damage.
  • Sudden loss or decrease of vision in one or both eyes
  • Sudden decrease or loss of hearing
  • Chest pain, fainting or severe dizziness during or after sex. Stop, call 911, and tell the emergency staff that you took sildenafil, because nitrate medicines must not be given with it.
  • Swelling of the face, lips or throat, trouble breathing, or a severe rash with blistering or peeling skin

Important Safety Information About Sildenafil

  • Nitrates: do not take sildenafil if you use any nitrate medicine, such as nitroglycerin, regularly or occasionally, in any form. Together they can cause a life-threatening drop in blood pressure.
  • Riociguat: do not take sildenafil with riociguat or other guanylate cyclase stimulators.
  • Heart and blood vessels: ED treatments should not be used by men who have been advised to avoid sexual activity. There are no controlled data in men with a heart attack, stroke or life-threatening heart rhythm problem in the past 6 months, unstable angina, heart failure, or resting blood pressure below 90/50 or above 170/110.
  • Vision: do not take it if you have ever had vision loss from NAION (non-arteritic anterior ischemic optic neuropathy). Tell the doctor if you have retinitis pigmentosa.
  • Prolonged erection: more caution is needed with sickle cell anemia, multiple myeloma or leukemia, and with Peyronie's disease or another deformity of the penis.
  • Bleeding disorders and active stomach ulcers: used with caution.
  • Allergy: do not take it if you are allergic to sildenafil or any ingredient. Non-medicinal ingredients differ between products, so ask your pharmacist if you have an allergy or lactose intolerance.
  • Products sold online without a prescription: sildenafil is a prescription drug in Canada. Get it only from a licensed pharmacy.

Drug Interactions

The interactions are the same for generic sildenafil and Viagra. Tell your doctor and pharmacist about everything you take. The main ones are:

  • Nitrates and riociguat: must never be combined with sildenafil
  • Alpha-blockers, such as doxazosin, and other blood pressure medicines: blood pressure can drop further, with dizziness on standing
  • Ritonavir: raises sildenafil levels about 11-fold. The maximum is 25 mg in 48 hours.
  • Erythromycin, saquinavir, ketoconazole, itraconazole and cimetidine: raise sildenafil levels, so a lower starting dose is considered
  • Rifampin and bosentan: lower sildenafil levels
  • Grapefruit juice: may raise sildenafil levels slightly
  • Other ED medicines, including tadalafil, and Revatio: not recommended together

Brands & DIN Number of Sildenafil

Brand Names

  • Viagra
  • Revatio

DIN (Drug Identification Numbers)

  • 02239766
  • 02239767
  • 02239768
  • 02544172

Key Takeaways

  • 1Sildenafil is the medicine in Viagra. Generic sildenafil tablets are also authorized in Canada.
  • 2Generic tablets come in the same 25 mg, 50 mg and 100 mg strengths as Viagra, but may look different.
  • 3The usual ED dose is 50 mg about 30 to 60 minutes before sex, with a range of 25 mg to 100 mg and no more than one dose a day.
  • 4Revatio is a different sildenafil product for pulmonary arterial hypertension, with its own dose.
  • 5Never take sildenafil with nitrates or riociguat.
  • 6Prices vary by pharmacy, strength and brand, so ask your pharmacist.
  • 7Sildenafil needs a prescription. BC residents can ask a BC-licensed doctor by phone whether it is right for them.

Frequently Asked Questions

Is generic sildenafil the same as Viagra?
It has the same medicinal ingredient in the same strengths: generic sildenafil tablets are authorized in Canada in 25 mg, 50 mg and 100 mg. Fillers, colour and shape can differ, so a generic tablet may not look like Viagra.
How much does sildenafil cost in Canada?
The price depends on the pharmacy, the strength, the number of tablets, whether you get generic or brand, and your coverage, so ask your pharmacist for current prices for both.
Does BC PharmaCare cover sildenafil?
Coverage depends on what sildenafil is prescribed for, your PharmaCare plan and any private insurance, and the rules change. Check with your pharmacist, BC PharmaCare or your insurer.
What is the difference between Viagra and Revatio?
Both contain sildenafil. Viagra is authorized for erectile dysfunction and is taken as needed. Revatio is used for pulmonary arterial hypertension, with its own dose and schedule. They are separate products and should not be taken together.
How do I get sildenafil in BC?
Sildenafil needs a prescription. You can see your family doctor, or book a phone visit with a BC-licensed doctor through Avee Health. Visits are covered by MSP with a valid BC health card. The doctor reviews your health history and decides whether sildenafil is appropriate. A prescription is not guaranteed. If one is written, it is sent to the pharmacy you choose.
Can I buy sildenafil without a prescription in Canada?
No. Sildenafil is prescription-only in Canada, both as Viagra and as a generic. A doctor needs to check your heart health and your other medicines first, because sildenafil must never be taken with nitrates or riociguat. Buy it only from a licensed pharmacy.
How long does sildenafil take to work and how long does it last?
It is usually taken 30 to 60 minutes before sex and can be taken up to 4 hours before. Blood levels peak about 60 minutes after a dose on an empty stomach, and a high-fat meal can delay this by about an hour. The half-life is 3 to 5 hours, so the effect fades over several hours.
What is the difference between sildenafil and tadalafil?
Both are PDE5 inhibitors for erectile dysfunction. They differ mainly in how long they act and how they can be taken. A doctor can help decide which suits you, and the same nitrate warning applies to both.
Written By
Avee Editorial

Avee Editorial

Avee Editorial Team

Updated:March 26, 2026