Tadalafil vs Sildenafil (Viagra): Key Differences Explained

Tadalafil and sildenafil are the two most commonly prescribed medications for erectile dysfunction in the UK. Both belong to the same class of drugs (PDE5 inhibitors) and work through similar mechanisms, yet they have important differences that may make one more suitable than the other depending on your needs and lifestyle.

This guide compares these two medications in detail to help you understand how they differ. It is for informational purposes only and does not constitute medical advice. Only a qualified prescriber can determine which medication is appropriate for your individual circumstances.

What Are Tadalafil and Sildenafil?

Both tadalafil and sildenafil are phosphodiesterase type 5 (PDE5) inhibitors. They work by increasing blood flow to the penis, making it easier to achieve and maintain an erection when sexually aroused.

Sildenafil is the active ingredient in Viagra, the first oral medication for erectile dysfunction approved in the UK (1998). It revolutionised ED treatment and remains widely prescribed today. Generic sildenafil has been available in the UK since the Viagra patent expired.

Tadalafil is the active ingredient in Cialis, which was approved several years after Viagra. It’s also available as a generic medication throughout the UK. Tadalafil is prescribed both for erectile dysfunction and benign prostatic hyperplasia (BPH).

For more background on tadalafil specifically, see our guide on what is tadalafil.

Key Differences at a Glance

Feature	Tadalafil	Sildenafil
Duration of action	Up to 36 hours	4-6 hours
Time to onset	30-60 minutes	30-60 minutes
Food effects	Minimal	Reduced effectiveness with high-fat meals
Dosing options	Daily (2.5-5 mg) or on-demand (10-20 mg)	Typically on-demand (25-100 mg)
Common brand name	Cialis	Viagra
Licensed for BPH	Yes	No

Duration of Action: The Primary Difference

The most significant difference between tadalafil and sildenafil is how long they remain active in the body.

Tadalafil: The “Weekend Pill”

Tadalafil can remain effective for up to 36 hours after taking a dose. This extended window has earned it the nickname “the weekend pill”. This doesn’t mean you’ll have an erection for 36 hours, but rather that you may be able to achieve erections during this period when sexually aroused.

This long duration offers flexibility and spontaneity, as you don’t need to time the medication as precisely around sexual activity. Many people find this reduces performance anxiety and makes intimate moments feel more natural.

Sildenafil: Shorter Duration

Sildenafil typically remains effective for 4 to 6 hours. This shorter window means you need to plan ahead and take the medication relatively close to when you anticipate sexual activity.

For some people, the shorter duration is actually preferable. It offers more control over when the medication is active in your system and may result in fewer side effects overall since the drug clears more quickly.

Time to Effect (Onset)

Both medications typically begin working within 30 to 60 minutes after taking a dose, though this can vary between individuals.

Sexual arousal is required for either medication to work. Neither will cause an automatic erection—they simply make it easier to respond to sexual stimulation.

Some factors that may affect how quickly these medications work include:

• Whether you’ve eaten recently and what you’ve eaten
• Your overall health and metabolism
• The specific dose you’re taking
• Individual biological variation

Impact of Food

Sildenafil and Food

High-fat meals can significantly slow down sildenafil’s absorption and reduce its effectiveness. If you take sildenafil after a large, fatty meal, it may take longer to work and may not be as effective.

For best results, sildenafil is often recommended to be taken on an empty stomach or after a light meal. This requirement can limit spontaneity for some people.

Tadalafil and Food

Tadalafil absorption is much less affected by food. You can take it with or without meals, including high-fat meals, with minimal impact on its effectiveness. This flexibility is another reason some people prefer tadalafil.

Dosing Flexibility

Tadalafil Dosing Options

Tadalafil offers two distinct dosing approaches:

On-Demand Use: 10 mg or 20 mg taken as needed, approximately 30 minutes before sexual activity. The effects can last up to 36 hours.

Daily Use: 2.5 mg or 5 mg taken once daily at the same time each day. This approach maintains a constant low level of the medication in your system, allowing for sexual activity at any time without needing to plan ahead.

The daily dosing option is unique to tadalafil among PDE5 inhibitors and is particularly appealing to people who prefer spontaneity or who have sex more frequently than twice per week.

For more information, see our articles on tadalafil 5mg daily and tadalafil 10mg and 20mg on-demand.

Sildenafil Dosing Options

Sildenafil is almost always used on-demand rather than daily. Standard doses are 25 mg, 50 mg, and 100 mg, taken approximately one hour before sexual activity.

Some people find they need to experiment with different doses to find what works best for them, always under medical supervision.

Side Effects Comparison

Both medications share similar side effect profiles because they work through the same mechanism. However, there are some differences in frequency and type.

Common Side Effects for Both

• Headaches
• Facial flushing
• Indigestion
• Nasal congestion
• Dizziness

Differences in Side Effects

Visual disturbances (seeing a blue tinge, blurred vision, or increased sensitivity to light) appear to be more common with sildenafil than with tadalafil. This occurs because sildenafil has a slightly higher affinity for PDE6, an enzyme found in the retina.

Back pain and muscle aches are more frequently reported with tadalafil. These typically appear 12-24 hours after taking the medication and resolve within 48 hours.

For detailed information on tadalafil’s side effects, read our comprehensive guide on tadalafil side effects.

Effectiveness: Which Works Better?

Clinical studies show that both tadalafil and sildenafil are highly effective for erectile dysfunction, with success rates typically above 70-80% when prescribed appropriately.

There isn’t conclusive evidence that one is definitively more effective than the other across all patients. Individual response varies significantly, and what works well for one person may not be ideal for another.

Some studies suggest that tadalafil may have a slight edge in patient satisfaction scores, possibly due to its longer duration and flexibility, but this doesn’t necessarily mean it’s more effective at producing erections.

Cost Considerations in the UK

Generic versions of both medications are now widely available in the UK, which has dramatically reduced costs compared to branded versions.

Generic Pricing

Generic tadalafil and generic sildenafil are broadly comparable in price when purchased through legitimate UK online clinics or pharmacies. Exact prices vary by provider and quantity, but neither has a significant cost advantage in the generic market.

NHS vs Private

Both medications are available on NHS prescription for certain eligible patients, though NHS availability has become more restricted in recent years. Most people in the UK now obtain these medications through private prescriptions, either from their GP, a private clinic, or a regulated online service.

For more information, see our guide on tadalafil on the NHS vs private prescriptions.

Daily Use vs On-Demand: Lifestyle Considerations

The choice between tadalafil and sildenafil often comes down to lifestyle and sexual activity patterns.

When Daily Tadalafil Makes Sense

You might prefer daily low-dose tadalafil if you:

• Have sex more than twice per week
• Value maximum spontaneity
• Don’t want to plan ahead for sexual activity
• Find on-demand dosing inconvenient or creates anxiety
• Also have BPH symptoms (tadalafil is licensed for both ED and BPH)

When On-Demand Medication Makes Sense

You might prefer on-demand medication (either tadalafil or sildenafil) if you:

• Have sex less frequently (once or twice per week or less)
• Prefer not to have medication in your system daily
• Want more control over when the medication is active
• Have found on-demand dosing works well for you

Other Approved Uses

Tadalafil for BPH

Tadalafil is licensed in the UK for treating both erectile dysfunction and benign prostatic hyperplasia (enlarged prostate). It can help relieve urinary symptoms associated with BPH, such as difficulty starting urination, weak stream, and frequent need to urinate.

For men who have both ED and BPH, tadalafil may address both conditions with a single medication, which can be more convenient and cost-effective.

Sildenafil for Pulmonary Hypertension

Whilst not directly relevant to ED treatment, it’s worth noting that sildenafil is also approved for treating pulmonary arterial hypertension under the brand name Revatio (though at different doses than for ED).

Tadalafil is similarly approved for pulmonary hypertension under the brand name Adcirca.

Drug Interactions and Contraindications

Both medications have similar contraindications and potential drug interactions because they work through the same mechanism.

Critical Interactions

Neither tadalafil nor sildenafil should be taken with:

• Nitrates (medications for chest pain/angina) - the combination can cause a dangerous drop in blood pressure
• Riociguat (for pulmonary hypertension)

Caution Required With

• Alpha-blockers (for prostate problems or high blood pressure)
• Other blood pressure medications
• Some antifungal medications
• Certain antibiotics
• HIV medications

Always inform your prescriber of all medications you’re taking, including over-the-counter drugs and supplements.

For information on specific interactions, see our guide on tadalafil, alcohol and blood pressure.

Half-Life and How It Affects You

The half-life of a medication is the time it takes for half of the drug to be eliminated from your body.

Sildenafil has a half-life of about 3-5 hours, which explains its 4-6 hour window of effectiveness.

Tadalafil has a much longer half-life of about 17.5 hours. This extended half-life is why tadalafil can remain effective for up to 36 hours.

The longer half-life means tadalafil stays in your system longer, which has both advantages (extended effectiveness window) and considerations (side effects may also last longer if they occur).

Which Should You Choose?

There’s no universal “best” choice between tadalafil and sildenafil. The right medication depends on your individual circumstances, lifestyle, and preferences.

Reasons to Consider Tadalafil

• You value spontaneity and flexibility
• You have sex more than twice weekly and might benefit from daily dosing
• High-fat meals are part of your regular diet
• You also have BPH symptoms
• You found sildenafil’s shorter duration limiting
• You prefer the option of taking a daily low dose

Reasons to Consider Sildenafil

• You have sex less frequently (once or twice per week or less)
• You prefer medication that clears your system relatively quickly
• You found tadalafil’s long duration inconvenient or caused prolonged side effects
• You’re comfortable planning ahead for sexual activity
• Sildenafil has worked well for you in the past

Trying Both

Some prescribers may suggest trying both medications (at different times, not together) to see which you respond to better and prefer. This approach can be helpful since individual responses vary.

Switching Between Medications

If you’re currently taking sildenafil but interested in trying tadalafil (or vice versa), discuss this with your prescriber. They can guide you on:

• Appropriate timing for switching
• Starting doses for the new medication
• What to expect during the transition
• How to assess which works better for you

Never switch medications or combine them without medical supervision.

Generic vs Branded Versions

Both tadalafil and sildenafil are available in generic and branded forms in the UK.

Generic tadalafil is equivalent to Cialis in terms of the active ingredient and effectiveness. The same applies to generic sildenafil and Viagra.

Generic medications must meet the same rigorous regulatory standards as branded versions. The main differences are price (generics are much cheaper) and sometimes the appearance or packaging.

For more information, see our article on tadalafil vs Cialis.

Safety Profile and Long-Term Use

Both medications have been used by millions of people worldwide and have well-established safety profiles when used as directed.

Long-term studies suggest that both tadalafil and sildenafil are generally safe for continued use under medical supervision. Regular check-ups with your prescriber are important to ensure the medication remains appropriate and effective.

Neither medication addresses the underlying causes of erectile dysfunction. They treat the symptoms, allowing for improved sexual function, but don’t cure the condition.

For information on long-term tadalafil use, see our article on tadalafil long-term use and safety.

Patient Satisfaction and Preference Studies

Research comparing patient satisfaction between tadalafil and sildenafil has yielded interesting results:

• Studies generally show high satisfaction rates for both medications
• Tadalafil often scores slightly higher in patient preference studies
• The longer duration and flexibility of tadalafil are frequently cited as reasons for preference
• However, individual preferences vary widely

These studies provide general guidance but don’t predict what will work best for any individual person.

Obtaining Tadalafil or Sildenafil in the UK

Both medications are prescription-only in the UK. You can obtain them through:

• Your GP with a private or NHS prescription (where eligible)
• A private doctor or clinic
• Regulated online pharmacy services that include a consultation with a UK-registered prescriber

Always ensure you’re using a legitimate, regulated service. The General Pharmaceutical Council (GPhC) regulates online pharmacies in the UK, and you can verify registration on their website.

For guidance on safe purchasing, see our article on how to buy tadalafil online in the UK.

Frequently Asked Questions

Can I take tadalafil and sildenafil together?

No. You should never take tadalafil and sildenafil together or on the same day. Both work through the same mechanism, and combining them increases the risk of serious side effects without improving effectiveness.

Which works faster?

Both typically begin working within 30-60 minutes. Some people report that sildenafil may work slightly faster on an empty stomach, but the difference is minimal and varies between individuals.

Which has fewer side effects?

The side effect profiles are similar. Some people tolerate one better than the other, but you can’t predict this in advance. If you experience problematic side effects with one medication, trying the other may help.

Is tadalafil stronger than sildenafil?

They’re not directly comparable in terms of “strength” because dosing differs. A 20 mg dose of tadalafil doesn’t mean it’s stronger than a 50 mg dose of sildenafil. Both are effective when prescribed at appropriate doses for your individual needs.

Can I switch from sildenafil to tadalafil?

Yes, many people switch between medications. Always do this under medical supervision. Your prescriber will guide you on appropriate dosing and timing when making the switch.

Which is better for daily use?

Tadalafil is the only PDE5 inhibitor with a licensed daily dosing option (2.5-5 mg). Sildenafil is not typically prescribed for daily use for erectile dysfunction.

Frequently Asked Questions (continued)

Does one work better for older patients?

Both medications can be effective across different age groups. Older patients may need dose adjustments due to changes in metabolism or other health factors, but this applies to both tadalafil and sildenafil. Your prescriber will consider your age and overall health when recommending treatment.

Which is safer with alcohol?

Both tadalafil and sildenafil can interact with alcohol. Drinking excessively whilst taking either medication can increase the risk of side effects such as dizziness and low blood pressure. Moderate alcohol consumption is generally considered acceptable with both medications, but this should be discussed with your prescriber.

Conclusion

Tadalafil and sildenafil are both highly effective treatments for erectile dysfunction, and the choice between them often comes down to personal preference, lifestyle, and individual response.

Tadalafil’s longer duration (up to 36 hours) and daily dosing option offer flexibility and spontaneity that many people value. Sildenafil’s shorter duration (4-6 hours) and well-established track record make it a reliable choice for on-demand use.

Neither medication is universally “better”—what matters is finding the treatment that works best for your individual situation. This requires:

• A proper medical assessment by a qualified prescriber
• Consideration of your lifestyle, sexual activity patterns, and preferences
• Possibly trying both medications to see which you respond to better
• Regular follow-up to ensure the medication remains safe and effective

If you’re considering treatment for erectile dysfunction or want to discuss whether tadalafil or sildenafil might be more appropriate for you, speak with a healthcare professional. They can provide personalised guidance based on your medical history and individual needs.

Remember, this information is for educational purposes and should not replace professional medical advice. Always consult a qualified prescriber before starting or changing any medication.