Viagra ( Sildenafil )

Viagra vs. Cialis vs. Levitra vs. sildenafil. How are they different?

All of these medications relax muscles in the penis and improve blood flow to treat ED. Although they act similarly, some differences may cause a medical professional to suggest one over the other.


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.

Searching for a simple answer to how to treat your ED can feel a bit like Alice in Wonderland. You chase after the one answer you need, but it takes a turn just as you’re about to grasp it. Suddenly you’re down the rabbit hole—in this case, the Internet rabbit hole—and more confused than ever about what treatment is right for you. You’ve likely run into multiple names of medicines, like Viagra, Cialis, Levitra, and sildenafil, but you’re no closer to a clear answer.


  • Erectile dysfunction, problems getting or maintaining an erection, is a common condition.
  • Viagra, Cialis, Levitra, and sildenafil all belong to the same class of drugs.
  • These medications relax muscles in the penis and improve blood flow to treat ED.
  • Although they act similarly, some differences may cause a medical professional to suggest one over the other.
  • Choosing between them should also come down to which fits best with your lifestyle.

It’s a common experience, especially since between 3 and 76.5% of men experience erectile dysfunction globally, according to a 2019 study (Kessler, 2019). Younger men aren’t immune to erectile dysfunction, more commonly known as ED, either. Roughly 8% of men 20–29 and 11% of men age 30–39 have erectile dysfunction, according to one study that looked at 27,000 men from eight different countries (Rosen, 2004). But this may only give us a limited idea of the true scope of the common condition as Rosen and his fellow researchers found that in men with ED in their study, only 58% had ever sought help from a medical professional for the condition.

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If prescription medication is needed to treat erectile dysfunction—which isn’t always the case, as things as simple as dehydration can cause ED—those same names pop up: Viagra, Cialis, Levitra, and sildenafil. It’s a lot easier to keep straight once you know that all of these fall into the same class of drugs called phosphodiesterase-5 inhibitors (PDE-5 inhibitors), which just means they all work in a similar way. Although erections are surprisingly complicated, these drugs do something simple to help: They all relax muscles in the penis and improve blood flow in order to treat ED.

What are PDE-5 inhibitors?

Movies and TV shows would have you believe it’s easy, maybe even too easy at times, to get an erection. But a lot of systems have to work together properly to make one happen, meaning there’s actually nothing easy or simple about it. Ignoring the emotional and psychological aspects of arousal, even the biology of an erection is complex. But there’s one step in the process where things tend to go wrong, and that’s where these medicines come in.

Before an erection can happen, a messenger called cGMP tells erectile tissue to relax, which allows blood to flow in. But at the same time, the blood vessels that take the blood back to your heart get compressed so that more blood is trapped in the penis. If all that goes right, you get an erection. The penis is able to relax thanks to an enzyme called phosphodiesterase-5 (PDE-5) that breaks down cGMP, ending the signal to the erectile tissue. This is where things tend to go wrong.

If you have too much phosphodiesterase or it takes over too soon, cGMP can’t do its job. PDE-5 inhibitors block this enzyme from breaking down this important messenger that kick starts the blood flow needed to get and maintain an erection. Higher levels of cGMP make this process easier. That’s the goal of all of these medications, though their exact chemical structure and the way that you take them differ.

What is Viagra?

Viagra is a brand name for sildenafil, which is just one type of PDE-5 inhibitor. The active ingredient is sildenafil citrate, and Viagra comes in three doses (25 mg, 50 mg, and 100 mg). The Food and Drug Administration (FDA) approved Viagra in 1998, and by the end of 2005, more than 27 million men worldwide (17 million of them in the United States) had been prescribed sildenafil for the treatment of ED (McMurray, 2007).

Viagra is an oral medication taken in anticipation of sex. It can be taken anywhere between 30 minutes and four hours ahead of sexual activity. Though Viagra can start to take effect and help achieve an erection in just 12 minutes, the medication reaches peak levels in your body after 30–120 minutes (Eardley, 2002). It can last in your body for up to four to five hours, but your age, health, and diet all affect the exact amount of time it will work. Viagra is also most effective when taken on an empty stomach.

The most common side effects of Viagra include indigestion, headaches, facial flushing, back pain, and stuffy nose. Although not as common, it can potentially cause priapism, a persistent and painful erection that can last more than four hours. Other serious, but less common, side effects include hearing loss (which can be sudden), severe low blood pressure, and vision loss, which can be in one or both eyes. You should not take Viagra if you have low blood pressure, heart problems such as a history of heart attack or chest pain, or uncontrolled high blood pressure.

Genuine vs. generic Viagra

As mentioned, Viagra is the brand name for sildenafil. “Genuine” Viagra is the medication sold under the brand name, while “generic Viagra” is another term for sildenafil. Sildenafil became available as a generic medication in December of 2017. Until then, only two companies (Pfizer and Teva Pharmaceuticals) could create this medication. Now that more companies can produce it, the price of generic sildenafil has been driven down even lower. Just like the branded version, generic Viagra comes in three doses: 25 mg, 50 mg, and 100 mg.

But Viagra isn’t the only brand name prescription medication that uses sildenafil. Another drug, Revatio, uses the same ingredient. Revatio, which comes in 20 mg doses, is approved by the FDA for a completely different purpose than Viagra, though the active ingredient is the same. Revatio treats pulmonary arterial hypertension (PAH), a condition in which the pressure in blood vessels that carry blood from your heart to your lungs is higher than normal, and some patients with more general pulmonary hypertension (PH) (Barnett, 2006).

There’s also a generic form of Revatio available. Although this may sound more complicated, it’s actually beneficial for people who may benefit from sildenafil. Generic Revatio comes in more dose sizes than the brand-name version. In addition to the 20 mg dose, it may be prescribed in 40 mg, 60 mg, 80 mg, and 100 mg doses. This allows more flexibility for patients to work with their healthcare providers to find the right dose that provides for the most benefit in facilitating erections and causes the least amount of side effects.

What is Cialis?

Cialis (generic name tadalafil) is another common prescription medication used to treat erectile dysfunction. The generic name of Cialis is tadalafil. Similarly to Viagra, Cialis works by blocking phosphodiesterase-5 (PDE-5), making it easier to get and keep an erection, but also improves blood flow. Cialis comes in doses of 2.5 mg, 5 mg, 10 mg, and 20 mg. Unlike Viagra, the effects of Cialis may take 1–2 hours to kick in but may last up to 36 hours. There’s also a generic version of Cialis (tadalafil) now available, which may be more affordable than the version sold under the brand name. Though Cialis can be taken as an as-needed treatment for ED at any of the doses, there’s another option for treatment with this prescription.

Daily Cialis is the only treatment of erectile dysfunction that’s taken daily instead of in anticipation of sexual activity. Only 2.5 mg and 5 mg are used as daily doses to treat sexual dysfunction. Taking the medication daily integrates it into your routine and eliminates the need to plan for sex. Like Viagra, it also should be taken on an empty stomach and may cause side effects such as priapism or sudden vision loss in one or both eyes.

What is Levitra?

Levitra (generic version vardenafil) is another common erectile dysfunction treatment. Similar to the other PDE-5 inhibitors, Levitra is taken as needed before sexual activity and comes in four doses (2.5 mg, 5 mg, 10 mg, and 20 mg). Although half of the medicine leaves your system after four to five hours, the effects of Levitra may last for up to eight hours. Levitra is also the only ED medication that can be taken with food, although a high-fat meal is not advised. A high-fat meal (fat content at or above 55%) can delay the absorption of the medication by about an hour and also decreases maximum blood flow.

Levitra has similar potential side effects to Viagra. Common side effects include headaches, facial flushing, nasal congestion, and upset stomach. Priapism is a potential side effect, as is sudden vision loss in one or both eyes. Levitra also increases the likelihood of QT prolongation (a change seen on an EKG), which can sometimes be followed by irregular heartbeats.

Which one is right for me?

Although all of these medications are PDE-5 inhibitors, they all have subtle differences in action. That means a healthcare professional may suggest one over the other for reasons specific to an individual’s health. It’s also important to discuss the medicines you’re taking with a medical professional as all of these treatments have potential drug interactions such as nitrates.

But there are also lifestyle factors to consider. Daily Cialis allows for more spontaneity in someone’s sex life over oral medications that require planning around sexual activity. Levitra has a longer duration of action, but you may prefer a short-acting medication if you experience some of the side effects of these prescriptions. Cost is another factor that may sway your decision. Sildenafil is the most inexpensive of the treatments, while Levitra tends to cost more. Overall, the decision comes down to many individual factors.

Drug How it’s taken Doses How long it takes to work How long it works Avoid Cost
Viagra Oral, as needed 25 mg, 50 mg, 100 mg 30-60 minutes 4-5 hours Food, alcohol, certain medications $$
Generic Viagra Oral, as needed 25 mg, 50 mg, 100 mg 30-60 minutes 4-5 hours Food, alcohol, certain medications $
Sildenafil Oral, as needed 20 mg, 40 mg, 60 mg, 80 mg, 100 mg 30-60 minutes 4-5 hours Food, alcohol, certain medications $ (cheaper than generic Viagra)
Cialis Oral, as needed 2.5 mg, 5 mg, 10 mg, 20 mg 1-2 hours Up to 36 hours Food, alcohol, certain medications $$
Daily Cialis Oral, daily 2.5 mg, 5 mg n/a n/a Food, alcohol, certain medications $$
Levitra Oral, as needed 25 mg, 50 mg, 100 mg 30-60 minutes Up to 8 hours Alcohol, certain medications $$$


  1. Barnett, C. F., & Machado, R. F. (2006). Sildenafil in the treatment of pulmonary hypertension. Vascular Health and Risk Management, 2(4), 411–422. doi: 10.2147/vhrm.2006.2.4.411,
  2. Eardley, I., Ellis, P., Boolell, M., & Wulff, M. (2002). Onset and duration of action of sildenafil for the treatment of erectile dysfunction. British Journal of Clinical Pharmacology, 53. doi: 10.1046/j.0306-5251.2001.00034.x,
  3. Kessler, A., Sollie, S., Challacombe, B., Briggs, K., & Hemelrijck, M. V. (2019). The global prevalence of erectile dysfunction: a review. BJU International, 124(4), 587–599. doi: 10.1111/bju.14813,
  4. McMurray, J. G., Feldman, R. A., Auerbach, S. M., DeRiesthal, H., & Wilson, N. (2007). Long-term safety and effectiveness of sildenafil citrate in men with erectile dysfunction. Therapeutics and Clinical Risk Management, 3(6), 975–981. Retrieved from
  5. Rosen, R. C., Fisher, W. A., Eardley, I., Niederberger, C., Nadel, A., & Sand, M. (2004). The multinational Mens Attitudes to Life Events and Sexuality (MALES) study: I. Prevalence oSf erectile dysfunction and related health concerns in the general population. Current Medical Research and Opinion, 20(5), 607–617. doi: 10.1185/030079904125003467,

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