- Sildenafil (Viagra) improves erections by increasing blood flow when you’re sexually aroused; it doesn’t create desire on its own.
- It works in about 30 to 60 minutes and lasts about 4 to 6 hours; a heavy, fatty meal slows it down.
- Never combine it with nitrates or poppers: blood pressure can drop dangerously.
- It’s a prescription drug in Canada, where generic sildenafil arrived early after a 2012 Supreme Court of Canada ruling.
Sildenafil is one of the most widely used medicines in the world. It’s effective, well studied and generally safe for healthy men, with one critical interaction to know about. This guide covers how it works, how it’s used, side effects, and how it compares with tadalafil (Cialis).
How sildenafil works
Sexual arousal releases nitric oxide in the penis, which raises a messenger called cGMP that relaxes blood vessels and lets blood flow in. The enzyme PDE5 breaks cGMP down. Sildenafil blocks PDE5, so the signal lasts longer and erections are firmer and easier to maintain. Without arousal, nothing happens.
Prescribed doses
For erectile dysfunction, the usual starting dose is 50 mg taken about an hour before sex, adjusted to 25 mg or 100 mg depending on effect and side effects, no more than once a day. The maximum is 100 mg. Lower starting doses are used for older men and people taking certain medicines.
Timing and food
- Works in about 30 to 60 minutes
- Effective for about 4 to 6 hours
- A heavy or fatty meal delays the effect; take it on a lighter stomach
- A drink or two is usually fine; heavy drinking makes erections harder and adds to blood pressure drops
Side effects
- Headache, flushing and nasal congestion (most common)
- Indigestion
- Temporary blue tint or light sensitivity in vision
- Dizziness
- Rare: sudden vision loss (NAION) or hearing loss; seek care immediately
- Rare: an erection lasting over 4 hours (priapism), which is an emergency
Never take sildenafil with nitroglycerin or other nitrate medicines, or with poppers. The combination can cause a dangerous drop in blood pressure. Use caution with alpha-blockers too.
Sildenafil vs tadalafil (Cialis)
| Sildenafil (Viagra) | Tadalafil (Cialis) | |
|---|---|---|
| Starts working | 30 to 60 minutes | 30 minutes to 2 hours |
| Lasts | About 4 to 6 hours | Up to 36 hours |
| Food effect | Fatty meals slow it | Little effect |
| Daily low-dose option | No | Yes |
See our ED tablets page for a release-time comparison.
ED as a health signal
Erectile dysfunction can be an early sign of heart disease, diabetes, high blood pressure or low testosterone. A family doctor, walk-in clinic or Canadian telehealth service can check. Steroid users often notice ED after a cycle, when natural testosterone is suppressed; see our PCT guide.
Generic sildenafil in Canada
In 2012 the Supreme Court of Canada invalidated Pfizer’s Canadian patent on Viagra, and generic sildenafil reached Canadian pharmacies years earlier than in many other countries. Sildenafil is a prescription drug in Canada (on Health Canada’s Prescription Drug List).
Buying in Canada
We stock Zionova Viagra (50 mg tablets) and Viagra Genetix Pharma (30 mg tablets), both in packs of 50, plus combination tablets with tadalafil. Check the strength on each product before use. Orders ship in a plain box from inside Canada.
Frequently asked questions
How long does Viagra last?
It works for about 4 to 6 hours after taking it.
Can I take Viagra with food?
Yes, but a heavy or fatty meal can delay the effect.
Is Viagra or Cialis better?
Viagra suits planned occasions; Cialis lasts up to 36 hours and is less affected by food.
Is sildenafil legal in Canada?
It’s a prescription drug in Canada (on Health Canada’s Prescription Drug List).
Can I take Viagra with nitrates?
No. The combination can drop blood pressure dangerously.
Products mentioned in this guide
This article is general information for adults in Canada, not medical advice. Talk to a doctor or pharmacist before using any prescription drug, anabolic steroid or research compound, and get bloodwork done. If you’re in crisis, call or text 9-8-8 (Suicide Crisis Helpline) any time.
