Sildenafil, first sold as Viagra, changed how erectile dysfunction is treated. It is one of the most studied medicines in the world, it works for most men who take it, and it has one interaction that can be dangerous. Here is how it works, what the Canadian label says and who should not take it.
- Sildenafil blocks the PDE5 enzyme, which helps blood flow into the penis during sexual arousal; it does not cause an erection on its own.
- Canadian labelling uses 50 mg about an hour before sex, adjusted to 25 or 100 mg, no more than once a day.
- It must never be combined with nitrate medicines such as nitroglycerin, because blood pressure can fall dangerously.
- Common side effects are headache, flushing, nasal congestion and indigestion.
How it works
During arousal, nerves in the penis release nitric oxide, which raises a messenger molecule called cGMP. cGMP relaxes smooth muscle in the blood vessels so blood flows in and an erection forms. The enzyme PDE5 breaks cGMP down. Sildenafil blocks PDE5, so cGMP lasts longer and the erection response is stronger. Without arousal, nothing happens, which is why it is not an aphrodisiac.
What the label says
The Canadian product monograph for erectile dysfunction starts at 50 mg taken about one hour before sexual activity, with adjustment to 25 mg or 100 mg depending on response and tolerance, and a maximum of one dose a day. Older men and people with certain liver or kidney problems may start lower. Those are label reference amounts, not personal advice; a doctor can check whether it is suitable.
Timing and food
Sildenafil usually starts working within 30 to 60 minutes and lasts around four hours. A heavy, fatty meal can delay its effect by an hour or so. That shorter window is the main practical difference from tadalafil.
Sildenafil or tadalafil?
| Sildenafil (Viagra) | Tadalafil (Cialis) | |
|---|---|---|
| Onset | 30 to 60 minutes | 30 minutes to 2 hours |
| Duration | About 4 hours | Up to 36 hours |
| Food effect | Fatty meals delay it | Little effect |
| Common side effects | Headache, flushing, blue-tinged vision in some | Headache, back and muscle aches |
Side effects
Most are mild and short-lived: headache, facial flushing, stuffy nose, indigestion and dizziness. Some men notice a blue tint or light sensitivity, because sildenafil also weakly affects an enzyme in the retina. Rare but serious problems include sudden vision or hearing loss and an erection lasting more than four hours (priapism), both of which need emergency care.
Nitroglycerin sprays and tablets, isosorbide and “poppers” (amyl or alkyl nitrites) combined with sildenafil can drop blood pressure to dangerous levels. Anyone who may need nitrates for chest pain must not take sildenafil.
Other interactions
Alpha-blockers for blood pressure or prostate symptoms can add to the blood-pressure-lowering effect. Some antifungals, antibiotics and HIV medicines raise sildenafil levels. Large amounts of alcohol make erection problems worse and add to dizziness. Anyone on regular medication should check with a pharmacist.
Who should be cautious
Men with recent heart attack or stroke, unstable chest pain, very low or uncontrolled high blood pressure, severe liver disease or certain inherited eye conditions should talk to a doctor first. Erectile problems can also be an early sign of heart disease or diabetes, so new difficulties are worth a check-up, not just a tablet.
Erectile problems and anabolic steroids
Steroid users sometimes develop erection problems, particularly with nandrolone or during recovery after stopping. That usually reflects hormone levels rather than blood flow, so bloodwork for testosterone, estradiol and prolactin is the first step.
Zionova, 50 mg tabletsViagra (Sildenafil)View product
Frequently asked questions
Does sildenafil work without arousal?
No. It improves the normal response to sexual stimulation; it does not create an erection by itself.
Can I take sildenafil every day?
The label allows at most one dose per day, taken when needed. Daily low-dose use is a tadalafil approach.
What if an erection lasts more than four hours?
Go to an emergency department. Prolonged erections can permanently damage tissue.
Educational information only. Nothing here is medical advice or a recommendation to use any product. Anabolic steroids are Schedule IV under the Controlled Drugs and Substances Act. Talk to a doctor and get bloodwork before and after using any compound.
