Daily Health

Cialis vs. Viagra: What You Need to Know

Before we answer your questions about Viagra and Cialis, we want to tell you something important. 


Erectile dysfunction is a lot more common than you think. According to a 2020 study by researchers for the International Society for Sexual Medicine, erectile dysfunction can see prevalence rates as high as 48.6%

That means you shouldn’t feel embarrassed if you can’t maintain an erection. 

Three key differences between Viagra vs. Cialis

  1. Cialis contains tadalafil, and Viagra contains sildenafil. They’re both phosphodiesterase-5 (PDE5) inhibitors that increase blood flow to the penis.
  2. Cialis can last for two days, while Viagra lasts for an average of two to four hours.
  3. Food slows down the absorption of Viagra, especially high-fat meals –– which means it may take longer for Viagra to work if you take it after you eat. Cialis works the same way whether you’ve eaten or not. 

Bonus fact: Cialis also treats the signs and symptoms of an enlarged prostate, called benign prostatic hyperplasia (BPH). Viagra doesn’t this condition. 

Is Viagra better because it was first?

Viagra, or sildenafil, became the first oral pill to treat erectile dysfunction in 1998, with a generic version released in 2017. But its use for ED was discovered by accident: Sildenafil was originally developed by Pfizer to treat high blood pressure and angina.

Cialis, on the other hand, was developed by Eli Lilly and Co, who modified components to create tadalafil, a potent and selective PDE5 inhibitor. Cialis was first approved in 2003 as the first and only ED pill clinically proven to last for up to 36 hours. One thing to note: Cialis can only be used once every 72 hours. A generic version was released in September 2018.

Then there’s vardenafil, otherwise known as Levitra. It’s virtually the same as Viagra, but some people prefer one over the other due to individual differences in effectiveness and side effects. 

Okay, but will I get harder with Viagra or Cialis?

The honest truth? Viagra and Cialis are equally effective at treating erectile dysfunction. 

Researchers have been comparing the two medications for years. In a meta-analysis looking at 16 trials comparing Viagra and Cialis, researchers didn’t find any significant differences between the two except for one thing: people preferred to take Cialis because it made them more confident. Why? It all comes down to Cialis’ staying power.

How long do Viagra and Cialis last?

Cialis has been affectionately called the “weekend pill” because of its long lifecycle. On average, Cialis works for about two days after you take it. 

Men and their partners have reported a preference for Cialis because they didn’t have to plan ahead as much for when they might have sex. In other words, Cialis let them be spontaneous. 

Viagra, on the other hand, lasts for two to four hours, with peak levels happening between 30–120 minutes. A higher dosage may mean longer effects, but that doesn’t mean you should insist on an increased dose. You should only take the dosage recommended by your doctor. 

Viagra is still a great medication for an evening when you know you’ll be having sex, but you’ll need to have a little more foresight. 

Which prescription works faster?

Viagra is absorbed quickly, and most people see effects within 30 minutes if they haven’t eaten. Keep in mind that when you take Viagra with a high fat meal, you could be delaying absorption by about an hour.

For most people at a normal dose, Cialis also starts to work within about 30 minutes. But because it’s a long-lasting medication, it can take two hours for Cialis to become fully effective.

What are the side effects of Viagra and Cialis?

The side effects of Viagra and Cialis are almost identical. 

Approximately 15% of people experience side effects of ED medication. Common side effects of Viagra and Cialis are: 

  • Dizziness
  • Headache
  • Flushing in the face
  • Upset stomach
  • Blurred vision
  • Changes in vision colour
  • A runny or stuffy nose or sore throat
  • Muscle or back pain

Less common side effects of Viagra and Cialis are:

  • Priapism — a prolonged erection that lasts more than four hours
  • Heart attack, stroke, cerebrovascular hemorrhage, palpitations, and arrhythmias
  • Vision loss
  • Hearing loss or a ringing in the ears
  • Seizures
  • Swelling and pain in the arms and legs

You should stop using Viagra or Cialis and seek immediate medical attention if you experience any of these symptoms:

  • Priapism — a prolonged erection that lasts more than four hours
  • Sudden vision change or loss 
  • Sudden hearing loss or ringing in the ears
  • An allergic reaction like lip or face swelling, wheezing or trouble breathing, hives.
  • Chest pain, shortness of breath, dizziness, or nausea during sex

Do other drugs interact with Viagra and Cialis?

Cialis and Viagra have similar drug interactions, but it’s universally known that they shouldn’t be used with any medication that lowers blood pressure. That means don’t pair ED prescriptions with nitrates, alpha blockers, antihypertensives, and riociguat

Cialis and Viagra also interact badly with some antibiotics, antifungals, and HIV protease inhibitor drugs. These drugs, all processed in the liver, can increase the level of Cialis and Viagra in the body to unwanted levels. 

Certain anticonvulsants like phenytoin or carbamazepine, and an antibiotic called rifampin, can decrease the effectiveness of Cialis and Viagra.

Last but not least: don’t take Cialis and Viagra with alcohol or grapefruit juice. You could be increasing your chances of experiencing side effects of the medications. 

Alcohol isn’t always conducive to maintaining an erection, anyway. 

What’s the dosage for each drug?

Cialis and Viagra are taken at different doses because of the differences in how long they last. 

A typical dose of Cialis is 10mg to start, which lasts 36 hours. But if that dose doesn’t produce great results, it can be increased to 20mg. Conversely, a dose can be reduced to 5mg if the side effects are too disruptive.


If someone wants to take Cialis on a daily basis, however, the recommended initial dose is 2.5mg once a day, which can be increased to 5mg if it’s not working. Cialis 10mg and 20mg can only be taken once every 72 hours.

Viagra, on the other hand, is taken at a dose of 50mg about one hour before sex. The dose may be increased to 100mg if the initial dose is ineffective or reduced to 25mg if the side effects aren’t great.

Final consideration: lifestyle factors can cause erectile dysfunction

It’s okay to seek treatment for erectile dysfunction. Everyone deserves the (consensual) sex life of their dreams––and if that means taking erectile dysfunction medication, that’s what it’s there for!

But before you go straight for the pills, you may want to consider other lifestyle factors that could be limiting your ability to get and maintain an erection. 

First, erectile dysfunction could be a sign of a more serious medical condition. Heart disease and diabetes have both been linked to ED. That’s why we highly recommend seeing a doctor if you’re experiencing ED, because they’ll be able to eliminate other more serious issues that could be causing it. 

Erectile dysfunction may also be linked to:

  • Smoking (tobacco restricts blood flow to veins and arteries — and your penis)
  • Obesity
  • Antidepressants 
  • Medications that treat high blood pressure
  • Drugs and alcohol

Finally, ED is often psychological –– stress, anxiety, and depression often go hand in hand with a disappearing erection. Our mental health is deeply connected to our sex life––if you’re stressed or depressed, your body isn’t exactly preoccupied with sending blood to your penis for an erection. 

To help you assess whether or not your mental health is affecting your sexual function, start by asking yourself the following questions:

  • Am I happy in my relationship(s) or as a single person?
  • Am I having the type of (consensual) sex that lights me up?
  • Am I communicating with my sexual partner(s) as effectively as I can be?
  • Am I experiencing abnormal stress levels lately?
  • Am I able to experience joy in other aspects of my life?

If you’re looking for mental health support in Canada, check out this resource to get started


We understand that the decision to try ED medication is personal. Learn more about which prescription may be right for you by having a chat with one of our doctors today.

Medically reviewed by
Dr. Kelly Anderson
Family Physician, MD, CCFP(EM)
Disclaimer

The views expressed here are those of the author and, as with the rest of the content on Active Ingredients, are not a substitute for professional medical advice, diagnosis, or treatment. If you have any medical questions or concerns, please talk to your healthcare provider.

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