Four popular drugs are widely available for treating the symptoms of erectile dysfunction (ED).

The drugs are phosphodiesterase 5 (PDE5) inhibitors, and their brand and generic names, respectively, are Viagra (sildenafil), Cialis (tadalafil), Levitra (vardenafil), and Stendra (avanafil).

They all have approval from the Food and Drug Administration (FDA), and they have the same function. However, there are some differences between them.

Understanding these differences can help a person choose the most suitable option.

Learn more about ED and premature ejaculation in our dedicated hub.

The drugs are all PDE5 inhibitors, and they all work in a similar way. They help relax the muscles and increase blood flow to the body.

This makes it easier for blood to enter the penis, and it allows people with ED to experience a lasting erection during sexual activity.

The drugs act relatively quickly, but the precise timing depends on the drug.

This table shows when to take the drug, the usual starting dose in milligrams (mg), and how long the effect is likely to last. It is of note that a doctor may adjust the dose for people with certain health conditions and those using other medications.

Drug nameWhen to take itStarting doseHow long it lasts
Viagra (sildenafil)30 minutes–4 hours before sex, but preferably 60 minutes before50 mg maximum once daily4–12 hours
Cialis (tadalafil)daily, at the same time each day10 mg maximum once daily17.5–36 hours
Levitra (vardenafil)60 minutes before sex10 mg maximum once daily4–12 hours
Stendra (avanafil)30 minutes before sex100 mg maximum once daily3–6 hours

Viagra, Cialis, Levitra, and Stendra are all drugs for treating the symptoms of ED.

A doctor will reach a diagnosis of ED if a person meets one of the following criteria:

  • never being able to get an erection
  • often being unable to get an erection
  • being able to get an erection but one that does not last long enough for sexual intercourse

Aspects of physical and mental health can contribute to ED, and a doctor will discuss these and lifestyle habits with the individual before prescribing these drugs.

Doctors may not prescribe the drugs to a person who has a cardiovascular health issue, which makes sexual activity dangerous for them.

The drugs are also not suitable for use with certain medications. Below, learn more about medications that can interact with these drugs.

Viagra, Cialis, Levitra, and Stendra have many similar side effects and interactions, but there are also some variations.

Anyone considering using these drugs should speak with a doctor first. The drugs may not be suitable for everyone, as they may affect a person’s existing health conditions or interact with other drugs the person is taking.

None of these drugs are suitable for an individual whom a healthcare professional has advised to avoid sexual activity because they have cardiovascular issues or are taking nitrates for a heart condition.

Using these drugs with nitrates or alpha-blockers may lead to a sudden fall in blood pressure, resulting in dizziness, faintness, and possibly falls and injuries.

An older study in rodents suggests that the following medications may increase the concentration of PDE5 inhibitors in the body, and therefore, an individual should consult a doctor before using ED drugs with any of them:

  • the antibiotics erythromycin and clarithromycin
  • ketoconazole, an antifungal and anti-dandruff agent
  • HIV protease inhibitors, such as ritonavir

Grapefruit juice is a CYP3A4 inhibitor and may increase the impact of these drugs.

The following table compares the possible adverse effects of the four drugs.

Side effectsheadache
nasal congestion
• flushing
• dizziness
• rash
• vision changes
• muscle aches and pains, or myalgia
• headache
• nasal congestion
• flushing
• indigestion
back pain
• limb pain
• muscle aches and pains
• headache
• nasal congestion
• flushing
• sinusitis
• indigestion
• flu-like symptoms
• back pain
• nausea
• high levels of creatine kinase
• headache
• nasal congestion
• flushing
• a sore throat
• back pain
Serious side effects (need immediate medical attention)• vision loss
priapism, which is an erection lasting 4 hours or more
• vision loss
• priapism
• vision loss
• priapism
• sudden hearing loss
• vision loss
• priapism
• hearing loss

Viagra drug interactions

Viagra may interact with the following drugs:

  • nitrates, such as nitroglycerin
  • alpha-blockers
  • drugs to decrease blood pressure
  • CYP4 inhibitors, such as ritonavir, ketoconazole, and erythromycin

Cialis interactions and warnings

People should not use Cialis with the following drugs:

  • nitrates
  • alpha-blockers
  • drugs to reduce blood pressure
  • CYP3A4 inhibitors, such as ketoconazole and ritonavir, as they can increase the impact
  • CYP3A4 inducers, such as rifampin, an antibiotic, as they may prevent Cialis from working

Levitra interactions and warnings

Individuals should not use Levitra if they have an irregular heartbeat or are using the following:

  • nitrates
  • alpha-blockers
  • drugs to lower blood pressure

A doctor may adjust the dose if the person has liver problems or is already using one of the following:

  • ritonavir, indinavir, saquinavir, or atazanavir, which are antiretroviral drugs doctors use to treat or prevent HIV
  • the antifungal medications ketoconazole or itraconazole
  • the antibiotics clarithromycin or erythromycin

Stendra interactions and warnings

A person should not take Stendra with nitrates or any strong CYP3A4 inhibitors, such as ketoconazole or ritonavir.

A doctor may adjust the dose if an individual is using alpha-blockers or a moderate CYP3A4 inhibitor, such as erythromycin, amprenavir, or diltiazem.

People should take care when using Stendra with the following, as they can lead to a drop in blood pressure:

  • drugs to reduce blood pressure
  • alcohol
  • alpha-blockers

Other concerns

Individuals should also take care that their product is an approved version and follow a doctor’s guidance when purchasing any of these drugs.

In 2020, for example, the FDA advised people not to purchase an imported product sold as a supplement called U.S.A Viagra.

The FDA warned that this product contains sildenafil but is not an approved form of Viagra and could be dangerous, especially for people with certain health conditions and those taking drugs that may interact.

The cost and availability of each drug can affect a person’s decision. All four drugs are widely available across the United States, but costs vary greatly.

Generic versions of Viagra, Cialis, and Levitra have approval from the FDA. These may be cheaper than brand-name drugs.

Here, find out how to buy ED drugs online and how much you can expect to pay.

Brand nameAvailable sincePros and cons
Viagra1998• possibly the best-known drug for ED
• generic version available
• suitable for using only when a person needs sexual stimulation
• effect lasting up to 12 hours
• can use with alcohol
Cialis2003• widely available and may be cheaper than Viagra
• suitable for people with benign prostatic hyperplasia
• generic version available
• suitable for daily use to keep the body ready for sexual stimulation at any time
• effect lasting up to 36 hours
• can use with up to 5 units of alcohol
Levitra2003• generic version available
• suitable for using only when a person needs sexual stimulation
• effect lasting up to 12 hours
• can use with alcohol
Stendra2012• adjustable dose, by a doctor, to use with certain drugs
• may have fewer adverse effects
• no generic version yet available
• effect lasting up to 6 hours
• can use with up to 3 units of alcohol

Here, learn more about the cost of Viagra and sildenafil and how to save on purchases.

While these drugs can help manage ED, a doctor may recommend trying making lifestyle changes before taking medication.

Actions that may help improve ED include:

It is advisable for anyone who has concerns about ED to consult a doctor, as they may be able to help. For example, they may prescribe one of these drugs.

If a person is already using one of these medications, they should contact a doctor if the drug is not helping or if they experience side effects such as vision changes. The doctor may recommend changing the dose or drug type.

Individuals should seek immediate medical attention if they experience any of the following:

  • vision loss
  • hearing loss
  • priapism

Viagra, Cialis, Levitra, and Stendra can help a person get an erection, but they will not cure ED. Other possible treatments include testosterone therapy and, in some cases, surgery.

Below, we answer some of the most common questions about Viagra, Cialis, Levitra, and Stendra.

Which is better: Viagra, Cialis, Levitra, or Stendra?

The choice will depend on a person and various factors, such as whether or not the person has sex regularly, other medications they are taking, and the cost and availability of the ED drugs.

Individuals should consult a healthcare professional to help them decide.

Do these drugs make you bigger?

They do not. They improve blood flow to the penis during an erection, but they do not change the size of the penis.

Which pill lasts longer?

The effects of Cialis (tadalafil) last up to 36 hours, but this only means a person can have an erection or multiple erections within that time. It does not mean they will have an erection lasting 36 hours.

Viagra, Levitra, Cialis, and Stendra can help a person with ED get and maintain an erection.

There are many side effects and interactions to consider. However, studies show that, with the right choice and correct use, these drugs can help a person overcome ED and engage in sexual activity.

It is of note that none of these drugs will provide sexual stimulation. The person will need stimulation in order to have an erection.

The only way to decide on the best drug may be through trial and error. Working directly with a doctor can help a person track side effects and decide which drug is most suitable for them.