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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.

The following table compares these two ED medications:

CialisViagra
Main ingredienttadalafilsildenafil
How long it takes to workaround 30 minutesaround 30 minutes
How long it lasts17.5–36 hours4–12 hours
When to take itdaily, at the same time each day30 minutes–4 hours before sex, but preferably 60 minutes before
Dosage5, 10, or 25 mg, up to once per day25, 50, or 100 mg, up to once per day
Pricefrom around $18 for 30 tablets of 20 mg of generic tadalafilfrom around $12 for 30 tablets of 100 mg of generic sildenafil
Common side effectsheadache
flushing
indigestion
nasal congestion
back pain
muscle pain
• pain in the limbs
• headache
• flushing
• indigestion
• nasal congestion
• back pain
dizziness
rash
Pros• people can take it with or without food
• lasts longer than Viagra
• can take the medication daily
• only take it when anticipating having sex
• sildenafil is one of the cheaper ED medications
• leaves the body quicker, which may make side effects last less time
Cons• may cause limb pain
• stays in the body longer than Viagra, which may mean side effects last longer
• have to take an hour before sexual activity, which may be unsuitable for people who prefer more spontaneous sex
• may cause dizziness and rash

Levitra and Viagra have the following similarities and differences:

LevitraViagra
Main ingredientvardenafilsildenafil
How long it takes to workaround 60 minutesaround 30 minutes
How long it lasts4–12 hours4–12 hours
When to take it60 minutes before sex30 minutes–4 hours before sex
Dosage2.5, 5, 10 or 20 mg, up to once daily25, 50, or 100 mg, up to once daily
Pricefrom around $47 for 10 tablets of 20 mg of generic vardenafilfrom around $12 for 30 tablets of 100 mg of generic sildenafil
Common side effects• headache
• flushing
• nasal congestion
• indigestion
sinusitis
• flu-like symptoms
• dizziness
nausea
• back pain
• headache
• flushing
• indigestion
• nasal congestion
• back pain
• dizziness
• rash
Pros• people can take it with or without food• sildenafil is cheaper than vardenafil
• has less side effects than Levitra
Cons• may cause flu-like symptoms
• unsuitable for spontaneous sex
• unsuitable for spontaneous sex

The following table provides an at-a-glance comparison between these two medications.

StendraViagra
Main ingredientavanafilsildenafil
How long it takes to workaround 15 minutesaround 30 minutes
How long it lasts3–6 hours4–12 hours
When to take it30 minutes before sex30 minutes–4 hours before sex
Dosage50, 100, or 200 mg, up to once daily25, 50, or 100 mg, up to once daily
Pricefrom around $385 for 6 tablets of 100 mgfrom around $12 for 30 tablets of 100 mg of generic sildenafil
Common side effects• headache
• flushing
• nasal congestion
nasopharyngitis
• back pain
• headache
• flushing
• indigestion
• nasal congestion
• back pain
• dizziness
• rash
Pros• fewer side effects than Viagra
• works within 15 minutes
• sildenafil is cheaper than Stendra
Cons• not available in generic form
• more expensive than sildenafil
• unsuitable for spontaneous sex

The following table compares Levitra and Cialis:

LevitraCialis
Main ingredientvardenafiltadalafil
How long it takes to workaround 60 minutesaround 30 minutes
How long it lasts4–12 hours17.5–36 hours
When to take it60 minutes before sexdaily, at the same time each day
Dosage2.5, 5, 10 or 20 mg, up to once daily5, 10, or 25 mg, up to once per day
Pricefrom around $47 for 10 tablets of 20 mg of generic vardenafilfrom around $18 for 30 tablets of 20 mg of generic tadalafil
Common side effects• headache
• flushing
• nasal congestion
• indigestion
• sinusitis
• flu-like symptoms
• dizziness
• nausea
• back pain
• headache
• flushing
• indigestion
• nasal congestion
• back pain
• muscle pain
• pain in the limbs
Pros• people can take it with or without food
• lasts less time than Cialis, so side effects may pass sooner
• generic Cialis is cheaper than generic Levitra
• has fewer side effects than Levitra
• allows spontaneous sex
Cons• not suitable for spontaneous sex
• has more side effects than Cialis
• may cause limb pain

The price of ED medication can vary widely depending on which medication a person chooses and whether they choose the generic or branded version of the drug.

Costs will also vary depending on whether a person’s insurance wil cover the price of the medication. People should always contact their insurance provider to see which medication it covers. Some companies may not offer coverage for branded medication.

Websites such as Optum Perks find and compare prices of medication and may offer discounts and coupons. People may find their medication at a cheaper price using a comparison site.

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.

ViagraCialisLevitraStendra
Headachexxxx
Nasal congestionxxxx
Flushingxxxx
Indigestionxxx
Nauseaxx
Dizzinessx
Vision changesx
Muscle aches and painsxx
Back painxxx
Limb painx
Sinusitisx
Flu-like symptomsx
High levels of creatine kinasex
Sore throatx
Vision lossxxxx
Priapismxxxx
Sudden hearing lossxx

If a person experiences vision loss, priapism, or sudden hearing loss while using any of these medications, it is important to contact emergency services for immediate medical attention.

Each of the medications in this article can interact negatively with other drugs. It is important to tell a healthcare professional about any other medication a person uses to reduce the risk of negative interactions.

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.

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.

The best ED pill will depend 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.

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.

Tadalafil and sildenafil, the active ingredients in Cialis and Viagra respectively, have similar effectiveness and studies show that both medications improve a person’s sexual confidence.

However, both people who take the medication and their partners prefer tadalafil over sildenafil as the effects last longer.

The manufacturers of Cialis recommend taking the medication around 30 minutes before sexual activity.

Cialis has a longer mechanism of action than Viagra, but it will not help people achieve harder erections than they would if they take Viagra.

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, 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.