What’s the difference between Cialis and Viagra?

Tadalafil (Cialis) is used to treat erectile dysfunction (ED, impotence; inability to get or keep an erection), and the symptoms of benign prostatic hyperplasia (BPH; an enlarged prostate) which include difficulty urinating (hesitation, dribbling, weak stream, and incomplete bladder emptying), painful urination, and urinary frequency and urgency in adult men. Tadalafil (Adcirca) is used to improve the ability to exercise in people with pulmonary arterial hypertension (PAH; high blood pressure in the vessels carrying blood to the lungs, causing shortness of breath, dizziness, and tiredness). Tadalafil is in a class of medications called phosphodiesterase (PDE) inhibitors. It works to treat erectile dysfunction by increasing blood flow to the penis during sexual stimulation. This increased blood flow can cause an erection. Tadalafil treats PAH by relaxing the blood vessels in the lungs to allow blood to flow more easily.

If you are taking tadalafil to treat erectile dysfunction, you should know that it does not cure erectile dysfunction or increase sexual desire. Tadalafil does not prevent pregnancy or the spread of sexually transmitted diseases such as human immunodeficiency virus (HIV).

Typical dosing for Cialis (tadalafil)

  • Cialis (tadalafil) is typically taken as a 10 mg dose about 30 minutes before sexual activity when needed. The dose can be adjusted anywhere from 5 mg to 20 mg depending on response Cialis (tadalafil) should not be taken more than once a day at any dose.
  • For people taking Cialis (tadalafil) daily, the usual dose is 2.5 mg to 5 mg by mouth once a day. This does not have to be timed based on sexual activity.

What’s the difference between Cialis and Viagra?

Cialis and Viagra are both PDE5 inhibitors used for the treatment of erectile dysfunction (ED).

  • Both only work when a man is sexually aroused.
  • Cialis lasts for around 36 hours compared with only 4 to 5 hours for Viagra.
  • Food does not affect the activity of Cialis, whereas food may decrease the effectiveness of Viagra.
  • Cialis can be used once daily, at a smaller dosage, and is also effective at treating benign prostatic hyperplasia (BPH).
  • Dosage of Cialis may need to be reduced in men with liver or kidney problems and risk of interactions may be higher than with Viagra.

What ingredients are contained in Cialis or Viagra and how do they work?

Cialis is the brand name for tadalafil and Viagra is the brand name for sildenafil.1,2 Both belong to a class of medicines known as phosphodiesterase type 5 (PDE5) inhibitors. PDE5 inhibitors work only in the presence of sexual stimulation, as they rely on the natural release of nitric oxide (NO), a chemical only released during sexual arousal. NO in turn activates other substances to relax the smooth muscle inside the penis to allow the inflow of blood and an erection to occur.

PDE5 inhibitors enhance the effect of NO.

Which drug was approved first?

On March 27 th, 1998, Viagra became the first oral pill, and the first PDE5 inhibitor, to be approved by the FDA to treat ED. A generic for Viagra was approved in March 2016  and released in December 2017.

Cialis was first approved for ED on November 21st, 2003. It was the third PDE5 inhibitor to come onto the market (after Levitra [vardenafil]).

Which one lasts for longer?

Cialis has an advantage over Viagra and Levitra in that it lasts for a lot longer – 36 hours, compared with 4-5 hours for Viagra and Levitra.  A generic for Cialis was approved in May 2018 and released in September 2018.

How quickly do Cialis and Viagra work and does food have any effect?

Cialis generally works within 16 to 45 minutes, and its activity is not affected by food.

Viagra generally works within 30 minutes, and its effect may be diminished if taken soon after a high fat meal (which may also delay how fast it works). For this reason, Viagra is best taken on an empty stomach.1,2,7

Effectiveness of all PDE5 inhibitors is similar; although reported effectiveness of Viagra, at 84% is slightly higher than that of Cialis at 81%. However, more men prefer Cialis because of its longer duration of effect.

What is the usual dosage of Cialis or Viagra?

Cialis can be taken on an as needed basis, or daily. Generally, daily dosages are smaller than as needed doses. Typically, Cialis is taken as a 10mg starting dose, prior to sexual activity. The effects of Cialis will last around 36 hours. The dosage may be increased to 20mg if 10mg is ineffective or reduced to 5mg if side effects are intolerable.1

When Cialis is taken for daily use, the recommended initial dosage is 2.5mg once daily, or 5mg for people who also have BPH. Timing of the daily dosage does not matter in people using it solely for ED; however, those with BPH are advised to take it at the same time each day. Do not take more than one dose a day but your doctor may consider an increase in dosage from 2.5 to 5mg if ineffective. Side effects of Cialis include headache and indigestion.1

Viagra is taken on an as needed basis, at a dose of 50mg, approximately 1 hour before sexual activity (although can be taken from 30 minutes to 4 hours before). The dose may be increased to 100mg if 50mg is ineffective or decreased to 25mg if side effects are intolerable.2 Viagra should only be taken once a day even though the effects wear off after approximately 4-5 hours. The main side effects are headache, flushing and indigestion.2 Rarely, color perception may be altered with Viagra. This side effect does not happen with Cialis.7

Cost of Viagra varies depending on tablet strength but is approximately $80 per tablet for the 50mg or 100mg strength. Cialis costs approximately $12 for the 5mg strength and $70 for the 20mg strength, per tablet.

All PDE5 inhibitors are contraindicated with nitrates.1,2 The longer duration of action of Cialis means it is at higher risk for drug interactions,1 and dosages may need reducing in men with kidney or liver disease. Cialis is not recommended in men who have had a heart attack or stroke within the past 6 months, with either uncontrolled high blood pressure or severely low blood pressure, unstable angina, or other conditions that make sexual activity inadvisable.

How should I take Cialis for the best results?

Take as directed

For as-needed dosing, take Cialis at least 30 minutes or more before sexual activity.

If your prescription involves taking Cialis daily, take it at the same time each day. This maintains steady levels of Cialis in your body.

Take as part of a lifestyle with physical activity

Smoking, heavy drinking, unmanaged stress, and an unhealthy diet can affect ED as well as how Cialis works, potentially leading to more side effects.

A healthy diet, increasing physical activity, and quitting smoking are important for wellness, physical health, and can affect the severity of ED.

Strategies to reduce stress and support your relationship with your partner can also improve sexual performance and well-being.

Communicate and stay relaxed

Working with a psychiatrist, therapist, or sex therapist can help you navigate strategies for the mental and emotional side of intimacy.

Other ways to improve your sexual performance include managing stress, working through relationship concerns, and treating performance anxiety.

If you’re anxious, stressed, depressed, or nervous, Cialis may not work as well. It’s important to relax and be aroused for the medication to work best.

What should I not take with Cialis?

High fat foods

Avoid high fat foods or heavy meals before taking Cialis and before sexual activity. High fat foods can affect how well Cialis works. It may also take longer to work.

Nitrates and other medications

Some medications can interact with Cialis and change its effectiveness. They include:

  • nitrates
  • antiseizure medications
  • HIV medications
  • certain antibiotics
  • oral antifungal medications
  • high blood pressure medications

Be sure to talk to your doctor or pharmacist about how to take all your medications to avoid interactions.

It’s important to avoid Cialis if you take chest pain (angina) and blood pressure medications in the nitrate category or alpha blocker drugs. They can lower your blood pressure to dangerous levels.

Alcoholic beverages

Use caution with alcohol consumption when taking Cialis. Too much alcohol can affect your ability to become aroused. It can also cause excessive low blood pressure, leading to headache, dizziness, and fainting.

Grapefruit and grapefruit juice

Avoid grapefruit with Cialis. It can increase the levels of the medication in the blood, causing increased side effects.

What else is important to know about taking Cialis?


In some people over 65 years old, Cialis may last longer because it takes more time for your body to process the medication. This affects how soon it leaves your body.

Poor kidney function can increase Cialis levels in your body, increasing side effects. Your doctor may adjust your dose in this case.

Heart and other conditions

If you’re over 65, have a heart condition, or liver- or kidney-related problems, your doctor may need to adjust your dose of Cialis and monitor how the medication works for you.

Fake Cialis

Avoid buying Cialis without a doctor’s prescription. PDE5 medications are some of the most commonTrusted Source counterfeit medications sold online. They can cause serious health risks.

Take as prescribed

Take Cialis exactly as prescribed by your doctor. Don’t take extra doses or change your dosing schedule without talking with your doctor to avoid side effects.

What are the side effects of Cialis?

Common side effects

The most common side effects of Cialis include:

  • back pain
  • diarrhea
  • flushing (redness of the face, neck, or chest)
  • headache
  • upset stomach
  • muscle aches

Serious side effects

Serious side effects of Cialis include:

  • priapism, a painful erection lasting longer than 4 hours, which can cause tissue damage
  • low blood pressure
  • changes in hearing and vision
The takeaway

ED is a common condition and can have many causes, including psychological and physiological reasons.

Risks of ED are higher with certain health conditions, so it’s important to openly talk with your doctor about your concerns. They can help you find the best treatment specific to your situation. This may include the need for ED medications.

Cialis is one of the most popular medications available for ED because it provides two types of dosing and lasts longer than other PDE5 inhibitor medications in this class, like sildenafil (Viagra).

There are several PDE5 inhibitor medications available, so discuss your needs and preferences with your doctor to select the medication best suited to you.

Remember, there are many causes for ED and many treatment options, including Cialis. Don’t be discouraged if Cialis doesn’t work the first time you try it. Your doctor can help adjust the dose or help you find other options to consider.