Urological Health
Penis Health
Erectile Dysfunction
The two ED medications are similarly effective but have key differences
ByKelly Burch
Updated on December 30, 2023
Medically reviewed byJamin Brahmbhatt, MD
Table of Contents
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Table of Contents
What Is Cialis?
What Is Viagra?
How ED Drugs Work
Cialis vs. Viagra
Differences
Cialis and Viagra are the most common medications used to treat erectile dysfunction (ED), and while both work to increase blood flow to the penis to support an erection, there are differences between the drugs. Both medications are phosphodiesterase type 5 (PDE5) inhibitors that work by increasing blood flow to the penis.
The major difference is that Cialis lasts longer and can be taken daily, giving you erections on demand. Viagra is always taken a few hours before it’s needed and offers less spontaneity.
Continue reading to learn more about Cialis vs. Viagra, including the side effects of each and the differences between them.
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What Is Cialis?
Cialis (tadalafil) is a type of PDE5 inhibitor that the Food and Drug Administration approved in 2003. Like other PDE5 inhibitors, it increases blood flow to the penis.
There are two different ways to take Cialis: as needed or daily. If you take the pill daily, the medication stays in your system constantly. This makes it easier to get an erection anytime you need one. This is a good option for people who frequently have sex and like flexibility and spontaneity in their sex lives.
The other option is to take Cialis at least 30 minutes before starting sexual activity. If you take the pill once, the effects of the pill last for about 36 hours. That means you’ll likely find it easier to get an erection during that time.
Cialis and Its Uses
Cialis is primarily for treating ED but can also treat an enlarged prostate. In addition, under the brand name Adcirca, tadalafil can also treat pulmonary arterial hypertension (PAH).
Side Effects
The common side effects of Cialis include:
- Headache
- Heartburn and indigestion
- Nausea and diarrhea
- Cough
- Muscle pain
- Drop in blood pressure
- Flushing
Some side effects of Cialis are an emergency. If you experience these you should speak with your healthcare provider immediately:
- An erection lasting longer than four hours
- Sudden vision changes, including blurred vision
- Sudden hearing changes, including ringing in the ears
- Dizziness
- Chest pain
- Hives, rash, or blistering
- Difficulty breathing or swallowing
- Swelling of the face or mouth
What Is Viagra?
Viagra (sildenafil) was the first erectile dysfunction pill the FDA approved, back in 1998. Like Cialis, it’s a PDE5 inhibitor that increases blood flow to the penis. The difference is that the effects of Viagra don’t last very long (only about four to six hours). Viagra is always taken before an anticipated sexual activity.
Viagra can only be taken once every 24 hours. So, even if you take it daily, there are times when the medication is not in your system, making it difficult to have an erection. Because of that, Viagra is most often used by people who occasionally have sex. The upside to Viagra is that you only take it when you need it.
Side Effects
Common side effects of Viagra include:
- Headache
- Heartburn
- Diarrhea
- Flushing
- Nosebleed
- Sleep troubles
- Numbness, burning, or tingling in the arms, hands, and feet
- Muscle aches
- Changes to vision, including sensitivity to light, seeing a blue tinge, or losing the ability to tell the difference between blue and green
If you experience other, more serious side effects, you should contact your healthcare provider immediately, including:
- Loss of vision or blurred vision
- Changes to hearing or ringing in the ears
- Dizziness and lightheadedness
- Fainting
- Chest pain
- Shortness of breath
As with Cialis, some people may experience a painful, prolonged erection that lasts longer than four hours. They also may experience itching while urinating and/or a rash.
| Viagra (sildenafil) | Cialis (tadalafil) | |
| Type | PDE5 inhibitor | PDE5 inhibitor |
| Dosage | 25-100 milligrams (mg), but only once every 24 hours | 2.5-5 mg daily, or 5-20 mg taken as needed |
| How Fast It Works | One hour (but can be taken 30 minutes to 4 hours before sex) | 30 minutes before sex, unless Cialis is taken daily |
| How Long It Lasts | Up to 36 hours | Between 4 and 6 hours |
| Side Effects | Headache, dizziness, chest pain, erection lasting more than 4 hours; can interact with other medications | Headache, muscle pain, problems with vision or hearing, prolonged erections; can interact with other medications. |
Understanding Dizziness as a Side Effect of Medications
How ED Drugs Work
PDE5 inhibitors work by blocking the breakdown of a substance known as cyclic guanosine monophosphate (cGMP). This, in turn, leads to more nitric oxide in the body.
Nitric oxide is a substance that causes blood vessels to relax. This leads to more blood flow to the penis, leading to stronger erections. Both Cialis and Viagra work in this way.
PDE5 Inhibitors
PDE5 inhibitors may be used to treat other conditions besides PAH. Research is under way to better understand how these drugs can help when treating heart-related conditions (like heart attack), diabetes, cancer, Alzheimer's disease, and more.
Nitric Oxide: Everything You Need to Know
Cialis vs. Viagra
Choosing the right ED pill can be intimidating. Talk with your healthcare provider about your sex life and desired use. Both medications are generic now and can be found at discounted rates, making them more accessible than ever before.
Which Works Faster?
Both Cialis and Viagra work quickly. If you’re taking Cialis as needed, you take the pill about 30 minutes before sex. Viagra can be taken as long as four hours to as little as 30 minutes before sex. It works best when taken one hour before sex.
Which Lasts Longer?
Cialis lasts longer. Cialis stays in your system for up to 36 hours and may provide support for erections during that entire time. Viagra generally only stays in your system for four to six hours.
Which Is More Effective?
Cialis and Viagra are equally effective. All PDE5 inhibitors are about 70% effective at helping people have better erections. That means seven out of 10 people who take these drugs as prescribed will have more frequent or longer-lasting erections.However, eating food, particularly high-fat food, can reduce the effectiveness of Viagra.
There’s no research available on whether Cialis or Viagra will give you harder erections. Because the mechanisms are the same, they’re likely similar. But if you achieve erections naturally, they offer no benefit, and they can't help with issues like anxiety that affect sexual function.
How to Prevent Erectile Dysfunction
Dosage
The dose of Cialis you need will depend on whether you’re taking it daily or as needed. Daily doses are often between 2.5 and 5 mg. The as-needed dose is usually 10 mg but can range from 5–20 mg.
The typical dose of Viagra is 50 mg. However, the dosage can range from 25–100 mg. Your healthcare provider will discuss which dose is right for you.
Safety
Because Cialis and Viagra are both PDE5 inhibitors, they have similar side effects and safety concerns. Talk with your healthcare provider about which might be best for you.
Which Is Better if You Have a Liver or Kidney Disorder?
Some people with severe kidney or liver disease may need to avoid certain PDE5 inhibitors. Cialis should be used in lower doses for people with mild liver disease or who are on renal dialysis. In some cases, low-dose Viagra may be an option for them instead.
People with liver or kidney also should discuss Levitra or Stanxyn (vardenafil) with their healthcare providers. Along with older adults, they may need to use a lower dose or different drug.
Keep in mind that some studies point to potential health benefits of PDE5 use in people with liver conditions, though much more research is needed to add liver or kidney disorders to the growing list of diseases that PDE5 drugs may one day treat.
Main Differences Between Cialis and Viagra
The main difference between Cialis and Viagra is how long each lasts. Cialis stays in your system for up to 36 hours, and you can take it daily. That means you can have erections whenever you want them. It’s also possible to take Cialis as needed, about 30 minutes before sex.
Viagra is always taken as needed, usually about an hour before sex. You can take Viagra daily, but because the medication only stays in your system for four to six hours, it will not be effective all day.
Talking to Your Healthcare Provider About ED
Talking to your healthcare provider about ED can be intimidating. However, it’s important to remember that sexual health is part of overall health. In addition, ED is extremely common. Healthcare providers have experience talking about ED and providing treatment options without any judgment or shame.
If you'd feel more comfortable talking with a healthcare provider virtually rather than in person, consider requesting an online ED prescription instead. But keep in mind that side effects and potential drug interactions (like taking nitrates with Viagra) are best discussed with your primary care provider.
Summary
Cialis and Viagra are both pills for treating erectile dysfunction. They are PDE5 inhibitors that allow for increased blood flow to the penis, leading to more frequent and harder erections. Because they are the same class of medications, they have similar side effects and effectiveness.
Cialis can be taken daily, providing constant treatment for ED for people who have sex frequently. There is also the option to take Cialis as needed. Viagra is always taken as needed, usually an hour before having sex.
10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Urology Care Foundation. Erectile dysfunction (ED).
Emling S. Viagra vs. Cialis: Is one right for you? American Association of Retired Persons (AARP).
MedlinePlus. Tadalafil. National Library of Medicine.
MedlinePlus. Sildenafil. National Library of Medicine.
Samidurai A, Xi L, Das A, Kukreja RC. Beyond Erectile Dysfunction: cGMP-Specific Phosphodiesterase 5 Inhibitors for Other Clinical Disorders. Annu Rev Pharmacol Toxicol. 2023 Jan 20;63:585-615. doi:10.1146/annurev-pharmtox-040122-034745.
Harvard Health Publishing. Can ED drugs really help your sex life?
Food and Drug Administration.Cialis (tadalafil) tablets, for oral use.
Food and Drug Administration.Levitra (vardenafil hydrochloride), for oral use.
Yu HM, Chung HK, Park KS. The PDE5 inhibitor udenafil ameliorates nonalcoholic fatty liver disease by improving mitochondrial function. Biochem Biophys Res Commun. 2021 Jun 18;558:57-63. doi:10.1016/j.bbrc.2021.04.038.
Pfizer. Viagra prescription drug information.
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By Kelly Burch
Burch is a New Hampshire-based freelance health writer with a bachelor's degree in communications from Boston University.
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