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Sildenafil vs. tadalafil: what’s the difference?

10 min read

Written by: 

Patricia Weiser, PharmD

Reviewed by: 

Peter Schlegel, MD, FACS

 and 

Raagini Yedidi, MD

Updated:  Mar 21, 2025

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Reviewed By

Peter Schlegel, MD, FACS

Peter Schlegel, MD, FACS, is a Ro Advisor, board-certified urologist, and male fertility expert.

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Key takeaways

  • Sildenafil and tadalafil are both prescription medications used to treat erectile dysfunction (ED) and pulmonary arterial hypertension (PAH) by improving blood flow. Tadalafil is also used to manage benign prostatic hyperplasia (BPH). 

  • For ED, sildenafil lasts about four hours, while tadalafil lasts up to 36 hours, offering more flexibility for spontaneous sexual activity. Sildenafil is taken as needed before planned sexual activity, whereas tadalafil offers both as-needed and daily dosing options.

  • Both medications start working in about 30 minutes. However, sildenafil’s effects can be delayed by high-fat meals, while tadalafil is unaffected by food.

Here's what we'll cover

Here's what we'll cover

Key takeaways

  • Sildenafil and tadalafil are both prescription medications used to treat erectile dysfunction (ED) and pulmonary arterial hypertension (PAH) by improving blood flow. Tadalafil is also used to manage benign prostatic hyperplasia (BPH). 

  • For ED, sildenafil lasts about four hours, while tadalafil lasts up to 36 hours, offering more flexibility for spontaneous sexual activity. Sildenafil is taken as needed before planned sexual activity, whereas tadalafil offers both as-needed and daily dosing options.

  • Both medications start working in about 30 minutes. However, sildenafil’s effects can be delayed by high-fat meals, while tadalafil is unaffected by food.

When it comes to treating erectile dysfunction (ED), two of the most well-known medications are sildenafil (Viagra) and tadalafil (Cialis). Both drugs belong to the phosphodiesterase-5 (PDE5) inhibitor class and work by increasing blood flow in the penis. While they share similarities, there are key differences between sildenafil vs. tadalafil in how long they last, how fast they work, and how they are taken.

This guide will compare tadalafil vs. sildenafil, including the drugs’ effectiveness, duration of action, side effects, and cost, to help you make an informed choice with your healthcare provider.

Viagra Important Safety Information: Read more about serious warnings and safety info.

Cialis Important Safety Information: Read more about serious warnings and safety info.

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What is sildenafil?

Sildenafil is a prescription medication used to treat erectile dysfunction (ED) and pulmonary arterial hypertension (PAH). It belongs to a class of drugs called phosphodiesterase-5 inhibitors (PDE5 inhibitors). The Food and Drug Administration (FDA) first approved sildenafil as Viagra for ED in 1998 and later as Revatio for PAH.  

Both brand-name and generic versions of sildenafil are available, but it’s not sold over the counter—you need a prescription from a healthcare provider. 

What is tadalafil?

Tadalafil is another prescription medication that belongs to the PDE5 inhibitor class. The FDA approved tadalafil for ED in 2003. Like sildenafil, tadalafil is also used to treat PAH. 

In addition, tadalafil is approved to reduce urination-related symptoms of benign prostatic hyperplasia (BPH), aka enlarged prostate.

Tadalafil is sold under the brand name Cialis for ED and BPH. It’s also marketed as Adcirca, Tadliq, and Alyq for PAH, and is available in both brand-name and generic versions. Like sildenafil, tadalafil is not available over the counter. You’ll need a prescription from a healthcare provider to get it.

Sildenafil vs. tadalafil: how do they work?

Sildenafil and tadalafil are both PDE5 inhibitors, a class of medications that improve blood flow by relaxing blood vessels. Both medications work via the same mechanism of action. 

ED is the inability to get and keep an erection adequate for satisfying sexual activity. Sildenafil and tadalafil work for ED by enhancing the effects of a natural compound called cyclic guanosine monophosphate (cGMP), which helps relax the smooth muscles in the penis, making it easier for blood to flow in. Normally, an enzyme called PDE5 breaks down cGMP. Sildenafil and tadalafil work by blocking PDE5, preventing it from breaking down cGMP. This allows cGMP to accumulate, relax the smooth muscles in the penis, increase blood flow, and improve erectile function. For ED, this means better blood flow to the corpus cavernosum, the spongy tissue inside the shaft of the penis, enhancing the ability to have a firm and sustained erection when sexually stimulated.

Tadalafil is also approved to treat benign prostatic hyperplasia (BPH), a condition where an enlarged prostate makes urination difficult. Tadalafil works to reduce BPH symptoms; it does this by enhancing blood flow, which can result in fewer urinary symptoms, including less urinary urgency. This also makes tadalafil a useful two-in-one treatment option for individuals who have both ED and BPH. Sildenafil isn’t FDA-approved for treating BPH.

Now that we’ve covered how sildenafil and tadalafil work in the body let’s get into the key differences: how fast they work and how long they last. 

Sildenafil vs. tadalafil: which works faster?

Both medications are effective for treating ED, but their onset times differ. 

Sildenafil starts working around 30 minutes to an hour after taking a dose on an empty stomach. Its absorption can be delayed if you take sildenafil on a full stomach, especially after eating a high-fat meal, such as fried food. These foods shouldn’t stop the medication from working, but it may take an hour longer for the effects to kick in compared to taking it on an empty stomach.

Sildenafil reaches its peak blood levels between 30 minutes to two hours after you take a dose. The recommended time to take sildenafil is about one hour before sex, but it may be taken anywhere from 30 minutes to four hours before planned sexual activity. You can figure out the optimal timing for you based on the way your body responds to the medication. 

Tadalafil also takes about 30 minutes to start working (as fast as 20 minutes in some people) and is not affected or delayed by food. For as-needed tadalafil, you may be able to have sex anywhere from 30 minutes to 36 hours after you take it. Tadalafil can also be taken several hours before sexual activity with equal effectiveness to taking it just before sexual activity.

If you’re taking daily tadalafil (for ED, BPH, or both), the timing of your dose or sex doesn’t matter. You can take tadalafil anytime of day, with or without food. Aim to take it around the same time each day to keep a steady amount of the medication in your system.

Note that ED medications like sildenafil and tadalafil don’t cause automatic erections. You still need sexual stimulation for an erection to happen with either drug. By increasing blood flow, sildenafil and tadalafil both make it easier to get an erection when you’re in the mood. 

Sildenafil vs. tadalafil: which lasts longer?

The main difference between sildenafil and tadalafil is how long they last. Sildenafil remains effective for ED for about four hours after you take it, or possibly longer in some cases. You should not take more than your healthcare provider prescribes, with a maximum of one dose per 24-hour period.

Tadalafil lasts up to 36 hours, allowing for a more extended period of spontaneity. Because of its longer duration, tadalafil is sometimes called the “weekend pill” because one dose lasts up to a day and a half. So, taking a dose on Friday evening can help you be ready for sex that night, anytime on Saturday, and even into Sunday morning.

Tadalafil also has a daily dosing option. If your healthcare provider prescribes daily Cialis, you’ll take a low dose once daily, at any time of day, whether you’re planning on sexual activity or not. This daily dosing option allows you to get an erection whenever arousal happens, which may be preferable for those who prefer more spur-of-the-moment intimacy. 

Sildenafil vs. tadalafil: side effects 

When comparing sildenafil and tadalafil for the treatment of ED, studies have found that both medications have similar safety and effectiveness. A meta-analysis of 16 clinical trials reported that, while both drugs are effective, more people preferred tadalafil. Tadalafil was also shown to improve sexual confidence in men with ED. This might be because it allowed for more sexual spontaneity and had longer-acting effects. When comparing side effects, tadalafil was more likely to cause muscle aches and back pain, while sildenafil was linked to higher rates of headache, stuffy nose, visual changes, and facial flushing.

Sildenafil side effects

Common side effects of sildenafil include headache, facial flushing, indigestion, nasal congestion, dizziness, and visual disturbances (such as a blue tint or other changes in color vision). 

Most sildenafil side effects are mild and temporary, but serious side effects are possible. If you experience severe or persistent symptoms (like an erection lasting beyond four hours), it’s important to seek emergency medical attention.

Sildenafil should not be taken by individuals taking nitrates, such as nitroglycerin for chest pain, or nitrites like “poppers,” as the combination can cause a dangerous drop in blood pressure. It is also contraindicated in people with a known allergy to sildenafil or any of its ingredients. Additionally, sildenafil should not be used with guanylate cyclase (GC) stimulators, such as riociguat, due to the risk of severe hypotension (low blood pressure). 

There are other precautions to consider before taking sildenafil. Always check with a healthcare provider before taking sildenafil to ensure it is safe for you, especially if you have a health condition affecting your heart, circulation, or blood pressure.

Tadalafil side effects 

While not a complete list, the most common side effects of tadalafil include headache, indigestion, back pain, muscle aches, nasal congestion, and facial flushing. These side effects are generally less common and/or severe than those experienced after sildenafil medication. Sometimes, these side effects go away as your body adjusts to the medication.

Similar contraindications and precautions for sildenafil also apply to tadalafil. Tadalafil should not be taken by people using nitrates, as it can significantly lower blood pressure. It is also contraindicated in people with a history of serious allergic reactions to any tadalafil product. Additionally, tadalafil should not be used alongside guanylate cyclase (GC) stimulators like riociguat, as this combination can lead to dangerously low blood pressure. 

Before taking tadalafil, tell your healthcare provider about all the medications and supplements you take and any medical conditions you may have. They can help determine if tadalafil is safe for you.

Sildenafil vs. tadalafil: doses and dosage schedules 

Next, we’ll cover the different forms and strengths, dosages, and tips for taking sildenafil vs. tadalafil. 

Sildenafil doses and dosage schedules

The dosage of sildenafil depends on the condition being treated. The drug is available in the following FDA-approved forms and strengths:

  • Oral tablets: 25 milligrams (mg), 50 mg, and 100 mg

  • Oral liquid suspension: 10 mg/mL

  • Solution for injection: 10 mg/12.5 mL 

For ED, the typical starting dose of sildenafil may be 50 mg or 100 mg, taken about one hour before sexual activity. Depending on how it works for you and whether any side effects are experienced, your healthcare provider may recommend adjusting your dose. Or, they may lower your dose to 25 mg if you experience bothersome side effects. The maximum dosage of sildenafil for ED is 100 mg once daily. 

Sildenafil can be taken with or without food, but taking it after eating a high-fat meal may delay its effects by an hour or so. If you want sildenafil to kick in faster, it’s best to take it on an empty stomach.

Some people may start with a lower dose of sildenafil for ED. Healthcare providers typically recommend a starting dose of 25 mg for people with severe kidney disease and mild-to-moderate liver problems. A lower dose is recommended in these groups because these factors may make the drug stay in your system longer than usual, which can enhance its effects (and side effects). Note that people with severe liver disease should avoid sildenafil altogether.

Sildenafil is also available in 20 mg tablets. This dosage was made available for pulmonary arterial hypertension but allows for easy dose adjustment. The active ingredient in the medications is the same.

Tadalafil doses and dosage schedules

Tadalafil is available as an oral tablet, in strengths of 2.5 mg, 5 mg, 10 mg, and 20 mg. It’s also available in an oral liquid suspension under the brand name, Tadliq, at a dose of 20 mg/5 mL. Ro also offers Daily Rise gummies which contain a daily dose of 7 mg tadalafil in a gummy form. The dosage and schedule vary depending on the condition being treated.

For ED, tadalafil can be taken either as-needed or once daily. The recommended as-needed dose is 10 mg before sexual activity, with adjustments to 20 mg or 5 mg depending on effectiveness and how well you tolerate any side effects. The maximum dose is 20 mg. Alternatively, once-daily dosing involves taking 2.5 mg at the same time every day, regardless of sexual activity, with an option to increase to 5 mg if necessary.

For benign prostatic hyperplasia (BPH), tadalafil is typically prescribed at a fixed dosage of 5 mg once daily, taken at the same time each day. This dosage is also recommended for people with both ED and BPH.

Tadalafil can be taken with or without food. However, special precautions should be taken for people with kidney or liver impairment. In mild to moderate kidney impairment, a starting dose of 5 mg for ED is recommended, but in severe cases, tadalafil should be taken with caution. Similarly, for mild to moderate liver disease, a 10 mg starting dose for ED may be used, but in severe cases, tadalafil should be avoided altogether.

As with any prescription medication, be sure to follow your healthcare provider’s instructions while taking sildenafil or tadalafil. Keep open communication with them about how the medication is working for you. They may recommend dosage adjustments based on individual response to treatment.

Sildenafil vs. tadalafil: cost

The cost of sildenafil and tadalafil varies depending on dosage, pharmacy, location, insurance, and other factors. Without insurance, discounts from services like GoodRx or SingleCare can significantly reduce the price for both medications.

Sildenafil cost

The cost of sildenafil varies without insurance. The retail price for sildenafil 100 mg can cost over $860 for thirty tablets. But most people don’t pay the full retail price. Several savings options are out there. 

Pharmacy discount cards, such as GoodRx and SingleCare, are free and accepted by most pharmacies. They offer discounts that can significantly reduce the cost of sildenafil. For example, a GoodRx discount coupon may lower the price of thirty 100 mg sildenafil tablets to $20.66, though discounts can fluctuate over time and where you are located. Brand name Viagra is significantly more expensive and may not have as many discounts available.

Generic sildenafil is covered by some Medicare and insurance plans. The cost with insurance depends on the specific plan you have. If it is covered, your insurance plan may limit the number of doses you can get each month for ED. You can check with your insurance provider to learn more about your coverage details. 

Tadalafil cost

The cost of tadalafil without insurance coverage or discounts can also be high. The generic is usually covered by insurance, including Medicare drug plans. You can confirm your specific benefits and any quantity limits by contacting the member services department at your insurance company.

GoodRx, SingleCare, and other prescription discount programs can help lower costs significantly. Some pharmacies could even offer generic tadalafil for under $1 per tablet when using such coupons. Without insurance, a 30-tablet supply of 5 mg of tadalafil costs around $19.32 with a GoodRx discount card applied, though this may depend on where you’re located. 

Sildenafil vs. tadalafil: which is better for ED?

Both sildenafil and tadalafil are highly effective for treating ED. The right medication for you depends on your personal preferences, lifestyle, and medical history.

  • If you want a medication that works within an hour or so and is taken only as needed for planned sex, sildenafil may be better for you. 

  • If you prefer a longer-lasting effect or the flexibility of a daily pill, or if you also have urinary symptoms, tadalafil may be a better choice for you.

Studies comparing overall satisfaction have found that people tend to prefer tadalafil 20 mg over sildenafil 50 mg for initiating ED therapy, but both medications are well tolerated. Another systematic review indicated that tadalafil significantly improved the psychological aspects of ED, including sexual confidence, and both patients and their partners showed a preference for tadalafil over sildenafil. 

If you try one of these medications and it isn’t working, talk with your prescriber. They can help determine if you could benefit from a dose adjustment. Or they may recommend switching from sildenafil to tadalafil (or vice versa) to see which one is better for you. 

Sildenafil vs. tadalafil: how do they compare?

Both medications are highly effective for treating ED, but tadalafil offers more flexibility due to its longer-lasting effects. Sildenafil, on the other hand, is a good choice for those who prefer short-acting, on-demand use. The chart below compares some of the key differences between sildenafil vs. tadalafil for ED. 

Bottom line: sildenafil vs. tadalafil

Sildenafil and tadalafil are commonly used to treat erectile dysfunction (ED), among other conditions. They belong to the same drug class and work by increasing blood flow in certain areas of the body.

  • Sildenafil is the active ingredient in Viagra, a prescription medication taken as needed about an hour before planned sexual activity. It’s also used to treat pulmonary arterial hypertension (PAH). 

  • Tadalafil, marketed as Cialis for ED, lasts significantly longer, up to 36 hours, offering more flexibility for those who prefer sexual spontaneity. Tadalafil is also used to treat PAH and to reduce signs and symptoms of BPH in men with an enlarged prostate (with or without ED). 

  • For ED, some men prefer sildenafil for its on-demand effect, while others choose tadalafil for its “weekend” duration or its once-daily dosing option to be ready for sex whenever the mood strikes. 

Schedule an appointment with a healthcare provider to see if sildenafil or tadalafil may be right for you. 

Frequently asked questions (FAQs)

DISCLAIMER

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.

Sildenafil (Generic of Viagra)
Erectile Dysfunction

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

March 21, 2025

Written by

Patricia Weiser, PharmD

Fact checked by

Peter Schlegel, MD, FACS and Raagini Suresh Yedidi, MD

About the medical reviewers

Peter Schlegel, MD, FACS

Peter Schlegel, MD, FACS, is a Ro Advisor, board-certified urologist, and internationally acclaimed expert in the treatment of male fertility. For nearly 20 years, Dr. Schlegel served as the chair of Urology at New York Presbyterian/Weill Cornell. He now focuses on providing the best patient care possible for urologic conditions through his private practice.

Raagini Yedidi, MD

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

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