AI summaries are provided for informational purposes only and do not replace professional medical advice.
Tadalafil (Cialis) lasts up to 36 hours and works on demand or as a daily low-dose option, while sildenafil (Viagra) works within 30–60 minutes and lasts about 4–6 hours. Your choice depends on how often you have sex, your lifestyle, and how your body responds. Both are prescription medications in Canada.
Erectile dysfunction (ED) affects a large number of Canadian men, and two of the most widely prescribed treatments are tadalafil and sildenafil. Although both belong to the same class of drugs called PDE5 inhibitors, they differ in how long they last, how quickly they work, and how they fit into your daily routine. This guide compares tadalafil vs sildenafil so you can have an informed conversation with your healthcare provider about which ED medication is right for you.
Tadalafil is the active ingredient in Cialis, a medication manufactured by Eli Lilly. Sildenafil is the active ingredient in Viagra, manufactured by BGP Pharma ULC in Canada. Both work by relaxing blood vessels in the penis to increase blood flow, which helps you achieve and maintain an erection when you are sexually stimulated.
Neither medication causes an erection on its own. Sexual stimulation is still required for the medication to work.
Both tadalafil and sildenafil block an enzyme called PDE5. This enzyme breaks down a molecule called cGMP, which relaxes the smooth muscle in the penis and allows blood to flow in. By blocking PDE5, both medications keep cGMP levels higher, which supports stronger and longer-lasting erections.
The key difference is how long each medication stays active in your body, which is determined by its half-life.
| Feature | Tadalafil (Cialis) | Sildenafil (Viagra) |
| Time to work | 30–60 minutes | 30–60 minutes |
| Duration of effect | Up to 36 hours | 4–6 hours |
| On-demand dose | 10 mg or 20 mg | 25 mg, 50 mg, or 100 mg |
| Daily dose option | Yes, 2.5 mg or 5 mg | No |
| Effect of food | Minimal | High-fat meals can delay absorption |
| Best for | Spontaneous sex, daily use | Planned sex, single occasion |
The most important difference between the two is duration. Sildenafil lasts about 4 to 6 hours, which is ideal if you want a medication that works for a single evening. Tadalafil lasts up to 36 hours, giving you a much wider window of opportunity and more spontaneity.
Because tadalafil lasts so long, it is also available as a low-dose daily tablet you can take once a day, so you’re ready at any time without planning.
Both medications typically start working within 30 to 60 minutes. However, food affects sildenafil more. A high-fat meal can slow down how quickly sildenafil is absorbed, which may delay its onset. Tadalafil is less affected by food so you can take it with or without a meal.
Sildenafil is available in 25 mg, 50 mg, and 100 mg strengths. The usual starting dose is 50 mg, taken as needed about one hour before sexual activity. The maximum recommended dose is 100 mg.
Tadalafil is available in 2.5 mg, 5 mg, 10 mg, and 20 mg strengths. The 10 mg and 20 mg doses are taken on demand before sexual activity, while the 2.5 mg and 5 mg doses are taken once daily for continuous effect.
Choose sildenafil if you prefer a medication for a single occasion and can plan. Choose tadalafil if you want more flexibility, a longer-lasting effect, or a daily option that keeps you ready at any time.
Your healthcare provider will also consider your overall health, other medications, and any underlying conditions such as heart disease or high blood pressure before recommending one.
Both medications share similar side effects, including headache, flushing, nasal congestion, indigestion, and back pain. Tadalafil is more commonly associated with muscle aches and back pain, while sildenafil is more commonly associated with visual changes such as a blue tint to vision.
Neither medication should be taken with nitrates, which are often used for chest pain, because the combination can cause a dangerous drop in blood pressure.
You should speak with a healthcare provider before starting either medication, especially if you have heart disease, have had a heart attack or stroke, have low blood pressure, or take nitrates. ED can also signal an underlying health condition, so a medical assessment is important.
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