Cialis vs Viagra: What's the Difference?

Cialis and Viagra are two of the most popular and well-known erectile dysfunction (ED) treatments available. They contain different active ingredients, but they’re both prescription-only PDE5 inhibitors and work in similar ways, as we’ll explain below.

In this guide we’ll compare the key differences between the two medications and how to talk with a Canadian-licensed clinician about your treatment options to find the best fit for you.

What is erectile dysfunction?

Erectile dysfunction is a condition characterized by difficulty achieving or maintaining an erection firm enough for penetrative sex. It’s very common in Canada, affecting nearly half (about 49%) of men aged 40 and older. [1]

There are many potential physical and psychological causes, including age, poor blood circulation, high blood pressure, obesity and stress. However, it’s very treatable, and prescription medication is a common way to manage the condition.

What is Cialis?

Cialis is the brand name of an erectile dysfunction treatment that contains the active ingredient tadalafil. It’s available in two dosing regimens: on‑demand Cialis and Cialis Once Daily (daily tadalafil). Both are authorized by Health Canada for treating ED. [2, 3]

Cialis Daily is a low dose (2.5mg or 5mg) tablet you take once a day, even on days you do not plan to have sex. This daily dose helps maintain a steady level of tadalafil in your bloodstream, which may help you get an erection whenever you're sexually aroused.

Regular Cialis is taken as and when you decide you want to have sex, typically 30–60 minutes before sexual activity. The usual dose is 10mg or 20mg, which provides a faster and higher concentration of tadalafil in the body. This can help you achieve firmer erections for up to 36 hours after taking the medication.

In Canada, tadalafil (Cialis) is also an authorized treatment for benign prostatic hyperplasia (BPH), a non-cancerous condition where the prostate gland enlarges as men age. [3]

What is Viagra?

Viagra is authorized in Canada for the treatment of erectile dysfunction, and it's been used for over two decades to improve sexual performance. It's a brand name for sildenafil, which is also the name of the active ingredient in the medication, and is available as a generic (unbranded) tablet.

Viagra is available in doses of 25mg, 50mg and 100mg. It’s also available as a 50mg film. It’s typically taken 30–60 minutes before sexual activity and remains effective for up to 4–6 hours.

How do ED treatments work?

Cialis and Viagra are both phosphodiesterase type 5 enzyme inhibitors, or PDE5 inhibitors for short. They use different active ingredients to treat erectile dysfunction by relaxing the muscles around your blood vessels, which improves blood flow to your penis. This should make it easier to get and maintain erections during sexual arousal.

PDE5 inhibitors don't increase sexual desire or libido. They only affect the physical side of erectile dysfunction and will only work in response to sexual stimulation.

There are also alternative treatments that you can try for ED, depending on what’s causing it. For example, exercises or lifestyle changes such as losing weight or cutting down on alcohol may help. [4] Or if you prefer a chewable tablet, there are alternative medications you can try.

Key differences: Cialis vs Viagra

Here’s a breakdown of the key differences between sildenafil and tadalafil treatments, to help you find which one is right for you.

How long do they last?

One of the biggest differences between Cialis and Viagra is how long they remain effective. Cialis can last up to 36 hours, which is why it's often nicknamed 'the weekend pill'. Viagra typically lasts for approximately 4–6 hours, narrowing your window of opportunity for sex.

How quickly do they work?

Cialis (on demand) may begin to work in as little as 15 minutes for some men, whereas Viagra typically takes approximately 30 minutes to take effect. Both should ideally be taken at least 30 minutes before sexual activity. Cialis Daily must be taken consistently to build up enough of the active ingredient in your body to be effective.

Food and alcohol

You can take Cialis with or without food. However, ideally you should take Viagra on an empty stomach, as it can take longer to work if you take it with food.

Neither should be taken with excessive alcohol, as this is a known contributing factor in erectile dysfunction and could also increase the risk of side effects. [5]

Daily dosing vs planning ahead

Cialis is available as a daily low-dose option (Cialis Daily), meaning you can be ready for sexual activity at any time without planning ahead. Viagra does not have an equivalent daily dosing option.

Side effects

Both medications share similar common side effects, including:

• Headaches
• Nausea
• Stuffy or runny nose
• Facial flushing
• Dizziness
• Indigestion (heartburn)

Seek urgent medical attention by calling 911 or attending your emergency department immediately if you experience any of the following severe side effects:

• Chest pain
• Sudden loss of vision
• A prolonged, painful erection lasting over 4 hours (priapism)
• Severe allergic reaction (anaphylaxis): difficulty breathing or swelling of the lips, mouth, tongue or throat

Who should not take them?

There are some cases where it’s not safe to take these treatments, such as certain medical conditions or potential drug interactions.

Do not use Cialis or Viagra if:

• You are taking nitrates. This is because Viagra and Cialis can enhance the effect of nitrates, which can lead to a significant drop in blood pressure.
• You have had a recent heart attack or stroke, or you have unstable angina or severe heart disease. [2, 3]

Always consult a qualified healthcare professional before starting either treatment, so they can assess your medical history and current medications.

So which is better: Cialis or Viagra?

Cialis and Viagra are both effective for treating erectile dysfunction, improving your blood flow to help you get harder erections during sexual arousal. They both have very similar common side effects, but the duration of action is what sets them apart.

Cialis stays in your body for longer, and is available in two forms (daily use and on-demand) which could make it easier for you to find a dose that suits your sex life.

Both erectile dysfunction treatments need to be prescribed by a healthcare professional, and they're also available as generic medications (tadalafil and sildenafil respectively) at a lower price with the same active ingredient.

Find out what treatment is suitable for you on our website.

References

1. Grover SA, Lowensteyn I, Kaouache M, Marchand S, Coupal L, DeCarolis E, et al. The prevalence of erectile dysfunction in the primary care setting: importance of risk factors for diabetes and vascular disease. Archives of internal medicine [Internet]. 2006 Autumn [cited 2026 July 8];166(2):213–9. Available from: https://pubmed.ncbi.nlm.nih.gov/16432091/
2. Government of Canada, Health Canada, Health Products and Food Branch. Drug Details - Drug and Health Product Register [Internet]. Hres.ca. 2020 [cited 2026 July 9]. Available from: https://hpr-rps.hres.ca/details.php?drugproductid=4928
3. Canada,. Drug Details - Drug and Health Product Register [Internet]. Hres.ca. 2016 [cited 2026 July 9]. Available from: https://hpr-rps.hres.ca/details.php?drugproductid=2744
4. Domes T, Najafabadi BT, Roberts M, Campbell J, Flannigan R, Bach P, et al. Canadian Urological Association guideline: Erectile dysfunction. Canadian Urological Association Journal. 2021 Aug 17;15(10).
5. Li S, Song JM, Zhang K, Zhang C Le. A Meta-Analysis of Erectile Dysfunction and Alcohol Consumption. Urologia Internationalis. 2021;105(11–12):969–85.