Cialis vs Viagra: The Key Differences Explained

Both Cialis and Viagra treat erectile dysfunction (ED) in a similar way. The main difference is how long their effects last. Viagra typically lasts anywhere between four and six hours, while Cialis can last for up to 36 hours. This distinction matters for a number of practical considerations, such as the amount of planning sex requires, the potential impact of food on the medication, and the better option for your routine (Huang and Lie, 2013).

If you're comparing Cialis vs Viagra for erectile dysfunction treatment to understand the key differences before discussing your options with a prescriber, this guide is for you. It compares how long each medication lasts, how food can affect treatment, possible side effects, cost, and suitability.

Key Takeaways

• Both Cialis and Viagra work in the same way. They're PDE5 inhibitors that support increased blood flow to the penis during sexual arousal.
• The active ingredient in Cialis, tadalafil, can remain effective for up to 36 hours. The active ingredient in Viagra, sildenafil, has a much shorter duration of action of about 4-5 hours.
• Food can affect the onset of Viagra. A large or high-fat meal may delay the absorption of sildenafil. In contrast, food doesn't affect tadalafil tablets in the same way (Huang and Lie, 2013).
• Both drugs require sexual stimulation to be effective. They support the physical processes involved in achieving an erection, but they don’t create sexual desire.
• Neither is suitable with nitrates. Nitrate drugs are used for chest pain and can lead to a life-threatening drop in blood pressure when combined with a PDE5 inhibitor.
• Brand versus generic can significantly affect the price. Generic sildenafil contains the same active ingredient as Viagra. Generic tadalafil contains the same active ingredient as Cialis. Both generic versions offer the same medical effectiveness as their branded counterparts at a lower cost.

Cialis and Viagra: What They Actually Are

Viagra is a brand name for sildenafil. Sildenafil is also available as a generic ED medication. Cialis is a brand name for tadalafil, which is also available as a generic medicine. Check out our sildenafil and tadalafil treatment product pages for more insights.

Both medications belong to a class of medications called phosphodiesterase type 5 (PDE5) inhibitors. During sexual arousal, the body releases nitric oxide, which contributes to a chain of chemical signals that relax smooth muscle and widen blood vessels in the penis. PDE5 inhibitors help maintain this process, allowing increased blood flow and making it easier to achieve and maintain an erection.

Cialis and Viagra can’t guarantee an erection or make you feel like having sex. Sexual stimulation is still necessary for either medication to work.

The Key Differences Between Cialis and Viagra

The main differences between Cialis and Viagra are the duration, food, side effects, and how much planning you want around sex.

How Quickly Does Each One Start Working?

The time an ED medication takes to work varies between people. Generally, sildenafil reaches the maximum blood concentration sooner than tadalafil, but this doesn't mean that a person will attain an erection at that exact time (Huang and Lie, 2013).

There are several factors that may impact the response, such as food, alcohol, sexual stimulation, other medication, and the underlying cause of ED. When considering Cialis vs Viagra, don't look only at onset. The difference is much greater when you consider how long the two drugs remain effective.

Viagra vs Cialis: Which One Lasts Longer?

Cialis lasts longer in the body than Viagra. Huang and Lie (2013) found that the half-life of sildenafil is approximately 4 hours, while that of tadalafil is approximately 17.5 hours. This longer half-life means that the effects of tadalafil last up to 36 hours.

This doesn’t imply that Cialis will keep an erection up for 36 hours. It means that you may be more likely to get and maintain an erection when you're sexually stimulated during that period. The extended duration makes Cialis more convenient if you want to have more flexibility in relation to sex. You don't have to schedule sex within a limited time frame.

However, don’t assume longer time automatically means better. If you prefer an ED medication that lasts for a shorter period, then Viagra may suit your routine better. Some of the unwanted Cialis effects may also last longer, as tadalafil stays in the body longer.

Why Food Matters More With Viagra Than With Cialis

Food is another practical difference between Cialis and Viagra. Sildenafil can take longer to work if you eat a high-fat meal before taking the medication. Huang and Lie (2013) found that a high-fat meal decreased the peak level of sildenafil and delayed the time needed to reach that peak. Similarly, the NHS guidance states that sildenafil might take longer to work after eating a large meal.

Food doesn't affect the rate or extent of tadalafil absorption. This difference matters because sex often follows dinner. If food regularly affects the effectiveness of an ED medication, discuss it with your prescriber. Don't change the dose or how you use the treatment.

Alcohol and Grapefruit With Both Medicines

Both treatments can be adversely affected by alcohol. The NHS recommends not drinking too much alcohol when taking sildenafil as it can make it more difficult to achieve an erection. Alcohol can also make it more likely to get low blood pressure with tadalafil, which can make you dizzy or lightheaded.

You should also avoid grapefruit or grapefruit juice with these medicines. NHS guidance warns that grapefruit can increase the likelihood of side effects with sildenafil and advises against drinking grapefruit juice while taking tadalafil.

Daily or On-Demand Erectile Dysfunction Treatment

Another notable difference between the two drugs is how doctors can prescribe them. Viagra is an on-demand treatment. Cialis can also be used on demand, but tadalafil is additionally licensed in a lower-dose daily regimen for appropriate patients.

Daily tadalafil keeps a more consistent amount of medication in the body, so you don't need to plan each tablet around sex. A prescriber will consider factors such as your general health, other medicines, and how frequently you expect to have sex before deciding whether this approach is appropriate. Don't choose or change a dose yourself. Let a prescriber assess which option fits your health and routine.

Does Cialis Work Better Than Viagra as an ED Medication?

While both Cialis and Viagra are established erectile dysfunction treatments, they don't work for everyone. The two medications contain different active ingredients, so it's difficult to determine which is "stronger." Let your prescriber choose an effective treatment based on your health, response, and other factors.

The effectiveness of Cialis and Viagra also varies between individuals. Sildenafil might work for one person, but cause bothersome side effects for another. Others might want Cialis's extended action or choose Viagra to suit their lifestyle preferences.

Talk to your doctor or prescriber if your first ED medicine doesn't work. Several factors can affect effectiveness, and sometimes changing treatment may be appropriate.

Side Effects of Cialis and Viagra

Cialis and Viagra can cause side effects, although not everyone experiences them.

Common Side Effects of Each Medicine

The common side effects of sildenafil include headaches, flushing, indigestion, dizziness, nasal congestion, and nausea. Some people also experience temporary visual changes, such as blurred vision or altered color perception.

Common tadalafil side effects include headache, indigestion, flushing, and nasal congestion. It can also cause back pain, muscle aches, and pain in the arms or legs.

This results in somewhat different patterns for the two drugs. Visual side effects are more common with sildenafil, and back and muscle pain are more typical of tadalafil. If side effects continue, become bothersome, or interfere with daily activities, talk to a health care provider; don't switch medications.

Serious Side Effects That Need Urgent Help

While rare, both drugs can cause serious side effects. A prolonged or painful erection, known as priapism, requires urgent medical attention. If an erection lasts for more than four hours, seek medical attention immediately because it can damage penile tissue.

Sudden hearing or eyesight problems can also require urgent assessment. If you notice symptoms of a serious allergic reaction, seizure, or heart problem, seek emergency help.

Chest pain also needs urgent medical attention. If you develop chest pain after taking an ED medication, tell the healthcare professionals the medication you took to help them determine the treatments they can give you safely.

Who Should Not Take Cialis or Viagra?

Cialis and Viagra aren't suitable for everyone, so it’s important to see a healthcare professional to assess your medical history and current medications that can interact with them.

One of the most significant interactions is with nitrates. Doctors prescribe nitrates to treat a variety of conditions, such as chest pain or angina. Don't take a PDE5 inhibitor together with nitrates because it can cause dangerously low blood pressure.

However, your doctor or prescriber should also consider if you:

• recently suffered from a heart attack or stroke
• have low blood pressure
• have significant liver or kidney problems
• suffer from some kind of blood disease such as sickle cell anaemia
• take other medications that might interact with an ED medication.

This isn't a complete list of contraindications or interactions. Before using Cialis, Viagra, or any other PDE5 inhibitor, inform your doctor or prescriber about other medications you're taking and medical conditions.

Cialis vs Viagra Price in the UK

The price could differ depending on the product, pack size, the pharmacy, and the brand or generic version. That's why current pharmacy prices offer a more useful comparison than fixed numbers that can quickly become outdated.

Why Branded Costs More Than Generic

At Curely, branded Viagra and branded Cialis both contain sildenafil and tadalafil, respectively. Generic versions contain the same active ingredients but are usually cheaper than the branded products.

In the UK, generic medicines must meet regulatory requirements for quality, safety and efficacy. Choosing a generic therefore does not mean choosing a medicine with a different active ingredient.

For Viagra specifically, our sildenafil vs Viagra guide explains the difference between the branded and generic versions in more detail. Prices can change, so check the current pharmacy price before deciding how much a treatment will cost you.

What the NHS Will and Won't Prescribe

The NHS prescribing position changed in October 2025. Generic sildenafil was already available for NHS treatment of erectile dysfunction without the Selected List Scheme restrictions that applied to some other ED medicines. From 1 October 2025, generically written prescriptions for tadalafil and vardenafil also stopped the need for the SLS endorsement (Community Pharmacy England, 2025).

There are still restrictions that apply to branded Cialis and Levitra when prescribed through the NHS for erectile dysfunction. The relevant criteria include certain medical circumstances, such as diabetes, multiple sclerosis, Parkinson's disease, prostate cancer, spinal cord injury, and renal dialysis.

These rules are about the NHS prescribing and reimbursement. They don't show that one ED medication works better than another.

Choosing Between Cialis and Viagra

There's no single erectile dysfunction treatment that suits everyone. The right choice depends on your health, other medication, and what you want from treatment.

Cialis may suit people who value a longer treatment window and less planning around sex. Food doesn't affect tadalafil's absorption the way it does with sildenafil. Tadalafil can also stay effective for up to 36 hours.

Viagra might be appropriate for individuals who prefer an on-demand medication with a shorter half-life. However, food may slow the action of sildenafil, especially after a large or high-fat meal.

Tadalafil is also licensed to treat the signs and symptoms of benign prostatic hyperplasia (BPH), or an enlarged prostate. Sildenafil doesn't have that indication. Having BPH alongside ED may therefore be relevant when a clinician considers your treatment options.

It's common for people to try one ED treatment and later discuss an alternative because of side effects, effectiveness, or practical preferences. A licensed prescriber can review your response and decide if changing medication is appropriate.

Erectile Dysfunction Treatment at Curely

At Curely, we provide erectile dysfunction treatment online. You complete a consultation covering your symptoms, medical history, and current medicines. A clinician then reviews the information to determine whether treatment is appropriate.

ED can sometimes relate to wider health issues. Conditions and other factors associated with erectile dysfunction include high blood pressure, high cholesterol, diabetes, cardiovascular problems, hormonal conditions, stress, and some medicines.

For that reason, treatment involves more than simply choosing between Cialis and Viagra based on how long each one lasts. If you're considering either medication, start with an erectile dysfunction consultation online so a prescriber can assess your health, current medication, and treatment preferences.

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Frequently Asked Questions

Can You Take Cialis And Viagra Together?

No. Don't take Cialis and Viagra together unless a clinician specifically directs you to do so. Both medicines belong to the same group of ED medication, known as PDE5 inhibitors, so combining them can increase the risk of side effects rather than improve your response. If one treatment doesn't help you achieve or maintain an erection, consult your prescriber instead of taking both (NHS, 2025).

Does Tadalafil Help With An Enlarged Prostate?

Yes. Tadalafil is approved to treat urinary symptoms caused by benign prostatic hyperplasia (BPH), or an enlarged prostate, as well as erectile dysfunction (NHS, 2025). This may make tadalafil relevant when someone has both conditions, although a prescriber still needs to assess which treatment is appropriate. An enlarged prostate isn't the same as prostate cancer, so watch out for new or changing urinary symptoms.

What Happens If Neither Erectile Dysfunction Treatment Works For You?

If Cialis and Viagra aren't working for you, your prescriber can review why and discuss other options. NHS primary care guidance recommends considering specialist referral when someone doesn't respond to at least two different PDE5 inhibitors and lists alternatives such as vacuum devices and alprostadil (NHS, 2025). Hormonal, psychological, and other health factors may also contribute, so let a professional investigate persistent ED instead of trying to work around it yourself.

Do Cialis And Viagra Work The First Time You Try Them?

Not always. NHS primary care guidance recommends assessing the response to a PDE5 inhibitor after several occasions of use rather than judging it after a single attempt (NHS, 2025). Alcohol, anxiety, tiredness, and other factors can affect what happens, so speak to your prescriber if the medication repeatedly fails to work.

How Long Do Cialis And Viagra Stay In Your System?

Cialis stays in your system longer than Viagra. Sildenafil has a half-life of around four to five hours, compared with approximately 17.5 hours for tadalafil, which helps explain why Cialis lasts longer (Huang and Lie, 2013). Half-life describes how quickly the body removes a medicine; however, it isn't the same as the length of time the medication can aid an erection.

Final Thoughts

The key differences in the Cialis vs Viagra comparison come down largely to duration and how each treatment fits your routine. Cialis lasts longer, with effects that can continue for up to 36 hours, while Viagra has a shorter treatment window. This doesn't make one stronger or more effective for everyone.

Your health, other medication, side effects, and response to treatment also matter. If you're weighing up Cialis and Viagra, an erectile dysfunction treatment consultation gives you the chance to discuss these factors with a prescriber and find an appropriate option for your needs.

References

• Community Pharmacy England. "Revisions to the Selected List Scheme." October 2025.
• Huang, S. A., and Lie, J. D. "Phosphodiesterase-5 (PDE5) Inhibitors in the Management of Erectile Dysfunction." Pharmacy and Therapeutics, volume 38, issue 7, 2013.
• Medicines and Healthcare products Regulatory Agency (MHRA). "MHRA Reclassifies Cialis Together Tablets to a Pharmacy Medicine." March 2023.
• Medicines and Healthcare products Regulatory Agency (MHRA). "UK Product License Information for Sildenafil and Tadalafil." Accessed September 2026.
• Midlands and Lancashire Commissioning Support Unit (NHS). "Primary Care Management of Erectile Dysfunction," Version 2.5, October 2025.
• National Health Service (NHS). "Erectile Dysfunction (Impotence)." NHS Health A to Z. Accessed September 2026.
• National Health Service (NHS). "Sildenafil (Viagra)." NHS Medicines A to Z. Accessed September 2026.
• National Health Service (NHS). "Tadalafil." NHS Medicines A to Z. Accessed September 2026.