PDE5 inhibitor (phosphodiesterase type 5 inhibitor)Prescription required in Canada

Viagrasildenafil citrate

Also sold as: Revatio (lower-dose for pulmonary arterial hypertension)

A prescription tablet for erectile dysfunction, taken as needed roughly an hour before activity.

Quick answer

What it is
A PDE5 inhibitor — it increases blood flow response in the penis, so the body's natural response to arousal becomes more reliable.
What it's used for
Erectile dysfunction. A lower-dose form of the same drug (Revatio) is used for pulmonary arterial hypertension.
Worth knowing
Taken as needed, usually 30–60 minutes before activity. A heavy or high-fat meal delays how quickly it works. It does not work without arousal.
Main safety point
It must never be combined with nitrate medications such as nitroglycerin — the drop in blood pressure can be life-threatening.

Viagra needs a prescription in Canada Pill4Me pharmacists in Chilliwack can help.

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Drug class

PDE5 inhibitor (phosphodiesterase type 5 inhibitor)

Use in Canada

Prescription-only in Canada — widely used for erectile dysfunction

DIN (Canada)

02244549, 02244550 +1 more

What is Viagra?

Sildenafil is approved in Canada for the treatment of erectile dysfunction (ED) — a condition in which a person is unable to achieve or maintain an erection sufficient for satisfying sexual activity. At lower doses under the brand name Revatio, it is also approved for pulmonary arterial hypertension. This page specifically covers sildenafil for erectile dysfunction.

How Viagra works

Sildenafil inhibits the enzyme phosphodiesterase type 5 (PDE5), which breaks down a signalling molecule (cGMP) in the smooth muscle of penile blood vessels. When PDE5 is blocked, cGMP levels remain elevated during sexual stimulation, causing the smooth muscle to relax and blood to flow in — resulting in an erection. Sildenafil requires sexual stimulation to work; it does not cause an erection automatically.

Forms and strengths

Tablets: 25 mg, 50 mg, and 100 mg. Standard starting dose is 50 mg. Generic sildenafil citrate became available in Canada in 2012 and is Health Canada-approved at a fraction of the Viagra brand price.

How Viagra is taken

Taken 30–60 minutes before sexual activity, once per day maximum. Can be taken with or without food, though a heavy or high-fat meal may delay onset. Do not take more than the prescribed dose or more than once in 24 hours. Your physician may adjust the dose (up to 100 mg or down to 25 mg) based on response and tolerability.

This is general information, not a dose for you. Dosing depends on the reason you are taking it, your kidney and liver function, your age, and everything else you take — follow the directions on your own label, and ask us if they differ from what you read here.

If you miss a dose

Sildenafil is taken as needed rather than on a schedule, so there is no missed dose to make up. Do not take more than one dose in 24 hours.

Side effects

Common — usually manageable

  • Headache — the most common side effect, caused by blood vessel dilation
  • Flushing — warmth or redness in the face, neck, or chest
  • Nasal congestion or runny nose
  • Dizziness or lightheadedness, particularly when standing up quickly
  • Indigestion or mild stomach upset
  • Temporary blue-tinted or altered vision at higher doses (usually mild and short-lived)

Get medical help for these

  • Sudden vision loss or significant visual changes — seek emergency care immediately (rare)
  • Sudden hearing loss or ringing in the ears
  • Prolonged erection lasting more than 4 hours (priapism) — this is a medical emergency; go to the ER immediately
  • Severe drop in blood pressure — especially if nitrates or excessive alcohol are also involved
  • Chest pain, irregular heartbeat, or shortness of breath during or after sexual activity

Important warnings

ABSOLUTE CONTRAINDICATION: Do not take sildenafil with nitrate medications — including nitroglycerin (GTN spray, Nitrostat), isosorbide mononitrate, isosorbide dinitrate, or amyl nitrite ('poppers'). The combination can cause a sudden, severe, potentially life-threatening drop in blood pressure.

If you have a heart condition that makes sexual activity inadvisable, sildenafil may not be appropriate. Discuss with your physician before starting.

Alpha-blockers (such as tamsulosin or doxazosin for enlarged prostate or blood pressure) can cause significant dizziness when combined with sildenafil — a lower starting dose and careful timing are required.

Some HIV medications (e.g. ritonavir) and antifungals (ketoconazole, itraconazole) significantly increase sildenafil blood levels — dose reduction to 25 mg is required. This interaction must be reviewed by a pharmacist or physician.

Who should take extra care

Nitrate medications
Nitroglycerin, isosorbide, and amyl nitrite ('poppers') must never be combined with sildenafil.
Heart disease
If sexual activity has been advised against for cardiac reasons, sildenafil is not appropriate until that is reassessed.
Alpha blockers
Tamsulosin, doxazosin and similar prostate or blood pressure medications can cause significant dizziness in combination — timing and dose need pharmacist input.
Liver or kidney impairment
Lower starting doses are used.
Eye conditions
Retinitis pigmentosa and a history of non-arteritic ischaemic optic neuropathy need physician direction.
Ritonavir and antifungals
These raise sildenafil levels substantially and require dose adjustment.

Who should not take it

  • Any patient taking nitrate medications for chest pain or heart disease — including nitroglycerin (GTN spray, Nitrostat), isosorbide mononitrate, isosorbide dinitrate, or amyl nitrite ('poppers'). This combination is absolutely contraindicated.
  • Patients using riociguat (Adempas) for pulmonary hypertension
  • Severe liver disease or hepatic impairment
  • Severely low blood pressure (hypotension)
  • Recent stroke or heart attack — timing depends on clinical assessment by your physician
  • Known hypersensitivity or allergy to sildenafil or any component of the formulation
  • Rare hereditary eye conditions (e.g. retinitis pigmentosa) — use only under explicit physician direction

Drug interactions

Nitrates (nitroglycerin, isosorbide mononitrate, isosorbide dinitrate, amyl nitrite) — absolutely contraindicated; life-threatening hypotension can result. Riociguat — contraindicated combination. Alpha-blockers (tamsulosin, doxazosin, prazosin) — additive blood pressure lowering; start sildenafil at 25 mg and allow time separation. Strong CYP3A4 inhibitors (ketoconazole, itraconazole, ritonavir, erythromycin, clarithromycin) — significantly increase sildenafil exposure; dose reduction to 25 mg required. CYP3A4 inducers (rifampin) — reduce sildenafil levels significantly. Alcohol — moderate amounts are generally acceptable but increase vasodilation and dizziness risk; avoid excessive alcohol on the day of use.

Commonly asked about alongside Viagra: Norvasc.

This is not a complete list. If you take several medications, or buy anything over the counter, a pharmacist medication review is the reliable way to catch interactions that matter.

Coverage in British Columbia

Sildenafil is not currently covered under BC PharmaCare for erectile dysfunction in most circumstances. Generic sildenafil has become significantly less expensive since generics became available in Canada in 2012, making it far more accessible than branded Viagra. Pill4Me dispenses Health Canada-approved generic sildenafil and can advise you on cost. All consultations are strictly confidential. Call 604-705-3644 for pricing or to discuss your prescription.

Coverage may depend on indication, PharmaCare plan and Special Authority requirements. Ask Pill4Me Pharmacy to check your coverage, or see BC PharmaCare.

Frequently asked questions

Do I need a prescription for Viagra (sildenafil) in Canada?
Yes — sildenafil is a prescription-only medication in Canada. It cannot be purchased over the counter, and you should be cautious of online sources that offer it without a prescription. To get sildenafil safely, you'll need to speak with a physician or nurse practitioner. Pill4Me's virtual clinic can connect you with a BC-licensed physician remotely if you don't currently have a prescription. Once prescribed, we'll fill it discreetly and answer any questions you have.
How long does sildenafil last?
The effects of sildenafil typically last 4–6 hours after taking it, though this varies by person. The medication doesn't produce a continuous erection — it makes the body's natural response to sexual stimulation more reliable during that window. Factors like age, other medications, and whether it's taken with food can all influence this. Your pharmacist can answer specific questions based on your situation.
Can I take sildenafil every day?
The standard way to use sildenafil is on an as-needed basis — taken 30–60 minutes before sexual activity, no more than once in 24 hours. Some physicians do prescribe a lower daily dose (typically 25 mg) as a continuous regimen for certain patients. This is not standard practice for everyone and should be specifically prescribed rather than self-initiated. If you're considering a change in how you take it, speak to your pharmacist or physician first.
Is sildenafil safe with heart medication?
It depends entirely on which heart medication. Sildenafil is absolutely contraindicated with nitrates — a combination that can cause a dangerous, sudden drop in blood pressure. This includes GTN spray, isosorbide nitrate tablets, and amyl nitrite. Other heart medications — including beta-blockers, ACE inhibitors, and some diuretics — are generally tolerated, though they may require dose adjustments or monitoring. Alpha-blockers (sometimes used for blood pressure or prostate conditions) can interact significantly. Always bring a complete list of your current medications to your pharmacist before starting sildenafil.
What if sildenafil doesn't work?
If sildenafil doesn't provide the results you expected, a few things are worth checking: Was it taken at the right time (30–60 minutes before)? Was there adequate sexual stimulation? Was a heavy meal taken before the dose? Was the dose appropriate? Some people respond better to a higher dose (100 mg max), and some do better on a different PDE5 inhibitor — tadalafil (Cialis) has a longer duration and is an alternative that works well for many people. Your pharmacist or physician can help assess next steps.
Is generic sildenafil the same as Viagra?
Yes. Generic sildenafil citrate contains the same active ingredient as Viagra, at the same doses, and has the same clinical effect. Generic versions became available in Canada in 2012 and are approved by Health Canada. The difference is cost — generic sildenafil is significantly less expensive than branded Viagra, making it far more accessible for ongoing use.
Can I get a prescription for sildenafil through a virtual clinic?
Yes — in many cases. Our virtual clinic connects you with BC-licensed physicians who can conduct a medical assessment and, if appropriate, prescribe sildenafil remotely. You'll need to be honest about your health history, current medications, and any heart conditions during the consultation. If the physician determines sildenafil is safe for you, the prescription is sent directly to Pill4Me. The process is straightforward, discreet, and handled with full confidentiality.

Related reading

Related medications

Norvasc (amlodipine besylate)

Conditions it’s used for

Erectile Dysfunction

Viagra needs a prescription in Canada

If you don't have one, our virtual clinic connects you with a BC-licensed physician by phone — register once and you can book appointments yourself. Any prescription comes straight to Pill4Me.

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Pill4Me Pharmacy is at 5625 Promontory Rd Unit 101, Chilliwack, BC. We deliver free to Chilliwack, Sardis, Promontory, Vedder and Yarrow, and you can reach a pharmacist directly at 604-705-3644.

Reviewed by a Pill4Me pharmacist · Last reviewed August 17, 2026

Medical disclaimer: This page is general educational information about Viagra and is not individualized medical advice, a diagnosis, or a treatment recommendation. Talk to your pharmacist or prescriber before starting, stopping, or changing any medication. BC PharmaCare coverage criteria change over time — confirm current coverage with us.