Cialis® vs. Viagra®: similarities and differences

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 and Viagra, 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.

Viagra (sildenafil) was the first drug approved by the US Food and Drug Administration (FDA) 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. 

Cialis (tadalafil) is an FDA-approved treatment for erectile dysfunction and benign prostatic hyperplasia (BPH), 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.

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.   

Both medications are part of a drug class known as phosphodiesterase 5 (PDE5) inhibitors. All PDE5 inhibitors are proven to be safe and effective for treating ED. They all 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.

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. 

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. 

Cialis vs. Viagra: which lasts 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 four 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.

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. The generic version also comes in 20 mg 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 could start with 2.5 mg or 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. 

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 brand-name 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.

Does insurance cover Cialis and Viagra? 

It depends on your insurance plan, but many plans generally provide coverage for some form of ED treatment. In general, insurance plans are less likely to cover brand-name Cialis or Viagra vs. generic tadalafil or sildenafil. It is also possible that your plan may cover other ED medications, such as Levitra (vardenafil) or Stendra (avanafil), but not Cialis or Viagra. 

To avoid overpaying for Cialis or Viagra, contact your insurance provider to understand what’s covered. They can help you understand which drug is covered and whether you need to take any additional action to receive coverage. For example, some insurance plans require prior authorization before they approve coverage, so your healthcare provider will need to submit a form on your behalf. Or they may have coverage limits for how many pills you can get at once, or how many refills you can receive.

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. Here is a quick look at the most common side effects of Cialis and Viagra affecting 2% or more of people.

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 not severe for most people.

Additionally, both Viagra and Cialis have the potential to cause rare, but serious, side effects. These may include:

• Priapism: PDE-5 inhibitors increase the risk of experiencing a painful, prolonged erection that lasts more than 4–6 hours. If your erection doesn’t go away after 4 hours, seek emergency medical treatment.

• Low blood pressure: Cialis and Viagra cause a drop in blood pressure, which can be dangerous for people who already have low blood pressure or are taking another medication to lower their blood pressure.

• Blurred vision: Viagra can cause vision changes like blurred vision, increased sensitivity to light, or a color tinge to vision. However, if you experience a sudden loss of vision in one or both eyes, it can be a sign of a non-arteritic ischemic optic neuropathy (NAION).

• Effects on the heart: It’s unclear to what extent PDE-5 inhibitors cause new heart issues. 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.

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 nitrates 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 may not be able to safely take Viagra or Cialis. Alpha-blockers are used to treat high blood pressure and some prostate issues, such as 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 impact 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.

---

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.

Editorial Guidelines | Medical Review Process

Current version

May 17, 2024

Written by

Chimene Richa, MD

Fact checked by

Raagini Yedidi, MD

---

About the medical reviewer

Raagini Yedidi, MD

Raagini Yedidi, MD, is an internal medicine resident and medical reviewer for Ro.