Cialis® vs. Viagra®: similarities and differences

Felix Gussone, MD - Contributor Avatar

Reviewed by Felix Gussone, MD, Ro, 

Written by Chimene Richa, MD 

Felix Gussone, MD - Contributor Avatar

Reviewed by Felix Gussone, MD, Ro, 

Written by Chimene Richa, MD 

last updated: Mar 08, 2023

8 min read

People seeking medical treatment for erectile dysfunction (ED) may feel overwhelmed by the options available, especially if their healthcare provider recommends an ED medication. 

When deciding between Cialis (tadalafil) and Viagra (sildenafil), it’s important to understand the key between the drugs, two commonly prescribed ED treatments. One key difference between Cialis and Viagra is how long the effects of the drug last in your body. Read on to learn more about the similarities and differences between Viagra and Cialis. 

Cialis Important Safety Information: Read more about serious warnings and safety info.

Viagra Important Safety Information: Read more about serious warnings and safety info.

Ro Sparks: Harder erections, faster than Viagra/Cialis (sildenafil/tadalafil). Get started with an online visit.

What are erectile dysfunction drugs?

Viagra (active ingredient sildenafil) and Cialis (active ingredient tadalafil) are drugs commonly used to treat erectile dysfunction (ED). ED is a common sexual dysfunction that may cause difficulties getting an erection, keeping an erection, or having morning erections. It affects 30–50 million American men and can prevent people from having a satisfying sex life.

Both Viagra and Cialis are phosphodiesterase type-5 enzyme (PDE-5) inhibitors. These drugs enhance blood flow to the penis, thereby improving erections. Other erectile dysfunction treatments in the PDE-5 inhibitor category include vardenafil (brand name Levitra) and avanafil (brand name Stendra). 

While PDE-5 inhibitors are effective at treating ED, they require sexual stimulation and arousal to work. 

What is Viagra?

Viagra (sildenafil) was the first drug FDA-approved to treat erectile dysfunction. Sildenafil, the active ingredient in Viagra, may also be used to treat pulmonary arterial hypertension (under the brand name Revatio). 

Some healthcare providers may use it “off-label” to treat conditions other than what’s FDA-approved. These conditions may include female sexual arousal disorder and Raynaud’s phenomenon. 

What is Cialis?

Cialis (tadalafil) is an FDA-approved treatment for erectile dysfunction and benign prostatic hyperplasia, a type of enlarged prostate. Under the brand name Adcirca, it can be used to treat pulmonary arterial hypertension. Like Viagra, some providers use it off-label to treat Raynaud’s phenomenon.

Viagra (sildenafil) vs. Cialis (tadalafil): what is the difference?

The biggest difference between Viagra and Cialis is how long the drugs last in your system. Cialis can last up to 36 hours while Viagra is taken on demand and lasts for up to 6 to 8 hours.   

All erectile dysfunction medications (PDE-5 inhibitors) are proven to be safe and effective for treating ED. And, all PDE-5 inhibitors function in the same way. However, there are some key differences between Viagra vs. Cialis that may make one drug the right choice for you:

  • The cost of each medication

  • Whether or not you can/should take the medication with food

  • How long the medication is effective

  • Side effects

  • Frequency of use

Let’s dive deeper into these key differences so you can decide which ED medication may be right for you.

Is Viagra or Cialis more effective?

Viagra and Cialis are both effective at treating erectile dysfunction when used as directed. One study comparing the two drugs showed that they were equally effective in treating erectile dysfunction.

However, differences between Cialis and Viagra might make one drug more effective for helping you achieve stronger, more timely erections based on your needs and lifestyle than the other. 

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Does Viagra or Cialis work faster?

Viagra and Cialis take approximately the same amount of time to work. Let’s look at each a little more closely. 

Viagra

Most people who take Viagra notice that it starts working around an hour after taking it, but it can be effective in as little as 30 minutes. It can take up to two hours to start working for some people. The recommendation is to take Viagra about 60 minutes before sexual activity. You can take Viagra with food or on an empty stomach. However, taking Viagra with a high-fat meal may make the medication take longer to kick in. 

Cialis

For most people, Cialis starts working in about 30 minutes. Like Viagra, you can take it with or without food, but unlike Viagra, a high-fat meal won’t impact the start time of the medication’s effectiveness. 

Does Viagra or Cialis last longer?

One of the key differences between Viagra and Cialis is how long the effects of the drug last in your body. 

In most cases, Viagra leaves the body in about 6 to 8 hours, and it’s taken “as needed” about 60 minutes before sex. The effects of Cialis, however, can last for up to 36 hours. This does not mean you will have an erection for 36 hours (an erection lasting 4 hours or longer is a dangerous condition called priapism)–it just means that you may be able to achieve an erection for 36 hours after taking the medication. For this reason, you can take a lower dose of the drug at the same time once daily, rather than just before you have sex. This can come in handy if you are unsure when sex may occur and can give you more flexibility. 

With both drugs, other factors may impact how long you are able to get and keep an erection (e.g., dosage, health conditions, additional medications, and overall health). And you need to be sexually aroused for either drug to work (in other words, you won’t get unwanted erections after taking these drugs without being sexually aroused).

What doses do Viagra and Cialis come in?

Available dosage is another key difference between Viagra and Cialis. 

Viagra

Sildenafil citrate (Viagra) comes in 25 mg, 50 mg, or 100 mg oral tablets. 

While most people start with the 50 mg dose, your healthcare provider may recommend a higher or lower dose, depending on your medical history. The maximum daily dose for Viagra is 100 mg per day.

Cialis

Tadalafil (Cialis) is available as an oral tablet in varying strengths: 2.5 mg, 5 mg, 10 mg, and 20 mg. 

When using Cialis as needed for ED, most people start with 10 mg at least 30 minutes before sex. However, if you are taking it daily for ED, you’ll likely start with 2.5 mg taken around the same time each day. Your healthcare provider may recommend a higher or lower dose depending on your medical history and other factors.

People using Cialis for BPH usually take a starting dose of 5 mg per day. 

The maximum daily dose for Cialis is 20 mg per day. 

Cost of Cialis vs. Viagra

Like most medications, what you pay for Viagra, Cialis, or their generic equivalents depends on a number of factors, including your health insurance coverage. And, also like most medications, the generic versions of Viagra and Cialis can cost significantly less than the name-brand medications (sometimes as much as 50% less or more).

That being said, Cialis can be more expensive than Viagra, depending on the dose. Cialis may be priced higher due to the longer duration of the effectiveness of each pill (36 hours as opposed to 6-8 hours for Viagra). If upfront cost is a concern, sildenafil might be the better option for you.

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Side effects of Viagra and Cialis

Since they belong to the same drug class, it’s not surprising that Viagra and Cialis have similar side effects. The risk of these side effects may depend on your medication dosage, medical conditions, and other factors. 

Priapism

Priapism is a painful, prolonged erection that lasts more than 4–6 hours and is a medical emergency. If the erection is not relieved, it can permanently damage your penis. All PDE-5 inhibitors, including Viagra and Cialis, increase your risk of developing priapism. Fortunately, this is a relatively rare serious side effect.

Low blood pressure

PDE-5 inhibitors work by encouraging the penis blood vessels to relax, allowing more blood to flow into the penis to maintain the erection. However, they affect the blood vessels throughout your body, not just those in the penis. When your vessels relax (or dilate), it causes your blood pressure to drop. 

In some cases, this is the effect we are looking for in a drug. But if you already have low blood pressure or are taking another medication to lower your blood pressure, PDE-5 inhibitors can make your blood pressure drop lower than intended, which can be dangerous.

Blurred vision

Rarely, people who take PDE-5 inhibitors report blurry vision due to an eye condition called non-arteritic ischemic optic neuropathy (NAION). This mainly happens in people with other risk factors for this condition. NAION can lead to changes in your vision that may or may not be permanent. Before starting a PDE-5 inhibitor like Viagra or Cialis, talk to your eye care professional about whether you are at an increased risk for developing NAION.

Effects on the heart 

The data is murky on how PDE-5 inhibitors affect the heart. It is unclear whether any new heart issues reported in clinical trials resulted from the medications, sexual activity, or other factors. For this reason, people with preexisting risk factors for heart disease (like high blood pressure, high cholesterol, diabetes, etc.) or a history of heart attacks or strokes should get medical advice from their healthcare provider before starting Viagra or Cialis.

Aside from the rare side effects above, there are also some common side effects of both drugs.

Viagra side effects

The most common side effects of Viagra include:

  • Headaches

  • Facial flushing

  • Indigestion/heartburn 

  • Back pain

  • Stuffy nose

  • Nausea 

Cialis side effects

The most common side effects of Cialis include:

  • Headaches

  • Indigestion/heartburn

  • Back pain

  • Muscle aches

  • Nasal congestion

  • Flushing

  • Pain in arms or legs

Cialis is less likely to cause facial flushing than Viagra, but more likely to cause back pain, muscle aches, and pain in arms or legs. If it occurs, the pain usually starts 12–24 hours after taking Cialis and goes away 48 hours after your last dose. People describe the back pain as diffuse lower back pain that may also affect your glutes or thighs that worsens with lying down. Fortunately, this pain is temporary and is not severe for most people.

How safe are Cialis and Viagra?

Cialis and Viagra are both safe and effective medications. However, as with any medication, taking Viagra or Cialis with certain additional medications or health conditions can cause dangerous side effects, as listed above. Seek medical advice from your healthcare provider before starting erectile dysfunction medications, including Viagra or Cialis. Be sure to discuss your medical history, as well as any over-the-counter supplements or prescription medicines you take, so you can best prevent any potential drug interactions. 

Given that both Viagra and Cialis are PDE-5 inhibitors, it is no surprise that they have similar drug interaction warnings. 

One of the most serious drug interactions with PDE-5 inhibitors, like Viagra and Cialis, happens with nitrates, drugs often used to treat chest pain (angina) or other heart conditions. Taking these drugs with PDE-5 inhibitors can lead to a severe drop in blood pressure with potentially fatal consequences. Examples include nitroglycerin and amyl nitrites, also called "poppers".

Similarly, if you take alpha-blockers, you should not take Viagra or Cialis. Alpha-blockers are used to treat high blood pressure and some prostate issues like benign prostatic hyperplasia (BPH). 

Since alpha-blockers may lower your blood pressure, combining them with PDE5 inhibitors can again lead to a dangerous situation where your blood pressure is too low. Examples of alpha-blockers include terazosin (brand name Hytrin) and tamsulosin (brand name Flomax).

Lastly, drugs that affect the CYP3A4 enzyme system may disrupt how your liver processes Viagra and Cialis, thereby increasing your risk of side effects. Examples of these drugs include ketoconazole, itraconazole, ritonavir, indinavir, and erythromycin. Grapefruit juice can also affect this enzyme system, so drinking large quantities could theoretically affect your sildenafil or tadalafil drug levels.

There may be other potential drug interactions with Viagra or Cialis. Seek medical advice from your pharmacist or healthcare professional if you have questions or concerns. 

If you struggle with erectile dysfunction, you’re not alone. Review the following differences and similarities between Viagra and Cialis, and make an appointment with your healthcare provider to determine which medication may be right for you to improve your sexual satisfaction.

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Viagra (sildenafil) vs. Cialis (tadalafil): differences and similarities

Viagra

Cialis

Generic form

sildenafil

tadalafil

What does it treat?

• Erectile dysfunction

• Pulmonary arterial hypertension (under the brand name Revatio)

• Erectile dysfunction

• Benign prostatic hyperplasia (BPH)

• Pulmonary arterial hypertension (under the brand name Adcirca)

How to take it?

• Take 30–60 minutes before sexual activity; effects last about 4 hours.

• Take 30–60 minutes before sexual activity; effects last up to 36 hours.

• Or, take a lower dose daily, as directed by your healthcare provider.

Most common side effects

Headaches, facial flushing, indigestion/heartburn, back pain, stuffy nose, nausea

Headaches, indigestion/heartburn, back pain, muscle aches, nasal congestion, flushing, pain in arms or legs

Risk of priapism?

Yes

Yes

Food

Can take with or without food; high-fat meals may make it take longer to work

Can take with or without food

Drug interactions

Low blood pressure

Low blood pressure

DISCLAIMER

If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.


How we reviewed this article

Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

Current version

March 08, 2023

Written by

Chimene Richa, MD

Fact checked by

Felix Gussone, MD


About the medical reviewer

Felix Gussone is a physician, health journalist and a Manager, Medical Content & Education at Ro.

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