Sildenafil vs Tadalafil: Differences, Duration & Safety

Sildenafil and tadalafil are two widely used medicines for erectile dysfunction (ED). Both belong to a class of medicines called phosphodiesterase type 5 (PDE5) inhibitors, but they differ in how long their effects last, how they are taken and how they interact with food and other medicines.

This guide compares sildenafil and tadalafil using information relevant to medicines authorised in the United Kingdom. It explains their main differences, potential side effects, treatment schedules and important safety considerations.

Sildenafil vs Tadalafil: Comparison Table

Feature	Sildenafil	Tadalafil
Well-known brand	Viagra	Cialis
Medicine class	PDE5 inhibitor	PDE5 inhibitor
Typical onset	Approximately 30–60 minutes	May begin working after approximately 30 minutes
Duration	Commonly around 4 hours	Up to 36 hours
Common UK tablet strengths for ED	25mg, 50mg, 100mg	2.5mg, 5mg, 10mg, 20mg
Daily treatment regimen	Generally used as needed for ED	Certain lower strengths are authorised for daily use
Food considerations	A large or high-fat meal may delay onset	Generally taken with or without food
Sexual stimulation required	Yes	Yes

These are general characteristics of authorised medicines used for erectile dysfunction. Individual effects vary, and the prescribing information for the specific medicine should always be followed.

How Do Sildenafil and Tadalafil Work?

Both medicines inhibit the PDE5 enzyme, helping blood vessels in the penis relax and supporting increased blood flow during sexual stimulation.

Neither medicine automatically produces an erection or directly increases sexual desire. Their effects depend on sexual stimulation and individual physiological responses.

The main difference is how long each medicine remains clinically active.

Which Lasts Longer: Sildenafil or Tadalafil?

Tadalafil has a substantially longer duration of action than sildenafil.

Sildenafil is commonly associated with an effective period of approximately four hours, although the actual duration varies.

Tadalafil may support erectile function for up to 36 hours after administration.

This does not mean that an erection lasts continuously throughout either period. Instead, the medicine may support erectile function when sexual stimulation occurs.

Which Works Faster?

Sildenafil commonly begins working within approximately 30–60 minutes. Tadalafil may also begin working within approximately 30 minutes.

Neither medicine is guaranteed to work at a particular time. Individual responses depend on factors such as metabolism, food intake, health conditions and other medications.

Onset alone is therefore not a reliable basis for deciding which medicine is more suitable.

Daily Treatment vs Occasional Use

One important distinction between sildenafil and tadalafil concerns their authorised treatment schedules.

Sildenafil

For erectile dysfunction, sildenafil is generally used when needed before anticipated sexual activity. The recommended maximum frequency for standard ED treatment is once daily.

Tadalafil

Tadalafil has authorised treatment regimens involving either occasional administration or lower-dose daily use.

For example, certain patients may be prescribed tadalafil 2.5mg or 5mg as part of a once-daily regimen. Tadalafil 10mg and 20mg are generally intended for use before anticipated sexual activity rather than continuous daily administration.

The appropriate regimen should be determined through individual medical assessment.

Does Food Affect Sildenafil and Tadalafil Differently?

Food can affect the onset of sildenafil. Taking sildenafil following a large or high-fat meal may delay its absorption and the time before its effects become noticeable.

Tadalafil can generally be taken with or without food, and ordinary meals do not usually have the same clinically important effect on its absorption.

This difference may be relevant when healthcare professionals discuss treatment suitability, but it does not determine which medicine is medically appropriate for an individual.

Comparing Side Effects

Sildenafil and tadalafil share several potential side effects because both belong to the PDE5 inhibitor family.

Side Effects Associated With Sildenafil

Headache
Facial flushing
Indigestion
Nasal congestion
Dizziness
Temporary visual disturbances

Side Effects Associated With Tadalafil

Headache
Indigestion
Facial flushing
Nasal congestion
Back pain
Muscle aches
Dizziness

These lists are not exhaustive. Both medicines can occasionally cause serious adverse effects, including sudden changes in vision or hearing, cardiovascular symptoms and prolonged painful erections.

Seek urgent medical assistance for chest pain, sudden loss of vision or hearing, or an erection lasting more than four hours.

Important Safety Considerations

Both sildenafil and tadalafil can interact with other medicines and may be unsuitable for people with certain medical conditions.

Nitrates and recreational nitrites: Neither medicine should be combined with nitrate medicines or recreational nitrites, commonly known as poppers, because of the risk of a dangerous fall in blood pressure.

Riociguat: Both medicines are contraindicated with riociguat because of the risk of excessive blood-pressure reduction.

Cardiovascular conditions: People with certain heart conditions, recent cardiovascular events or unstable blood pressure require appropriate medical evaluation.

Other medications: Certain antifungal medicines, antibiotics, HIV treatments and alpha-blockers may affect the suitability or dosing of PDE5 inhibitors.

Can Sildenafil and Tadalafil Be Taken Together?

Sildenafil and tadalafil should not be combined without specific medical direction.

Because both inhibit PDE5, combining them can increase the risk of adverse effects, including excessive blood-pressure reduction.

Using two different erectile dysfunction medicines together does not automatically improve treatment effectiveness or safety.

Viagra vs Cialis: Is There a Difference?

Viagra is a brand name for a medicine containing sildenafil, while Cialis is a brand name for a medicine containing tadalafil.

Authorised generic medicines containing these ingredients must meet applicable regulatory requirements for quality, safety and efficacy.

Although Viagra and Cialis are frequently compared, the underlying distinction is between their active ingredients rather than simply their brand names.

What About Products Marketed Internationally?

Products containing sildenafil or tadalafil are marketed internationally under numerous brand names and in different strengths and formulations.

However, the presence of the same active ingredient does not mean that two products have equivalent regulatory approval or manufacturing standards.

In the UK, marketing authorisation applies to individual medicines. Products marketed under names such as Kamagra are not authorised UK medicines and should not be confused with authorised sildenafil or tadalafil products.

Which Medicine Is More Suitable?

There is no single medicine that is automatically the most appropriate treatment for everyone experiencing erectile dysfunction.

Healthcare professionals consider factors such as the underlying causes of ED, existing medical conditions, other medicines, treatment response, adverse effects and individual preferences.

The longer duration of tadalafil may be relevant to some treatment plans, while sildenafil’s shorter duration may be relevant in other circumstances.

Persistent erectile dysfunction should be medically assessed because it can sometimes be associated with conditions such as cardiovascular disease or diabetes.

Frequently Asked Questions

Is tadalafil stronger than sildenafil?

Not necessarily. Sildenafil and tadalafil have different pharmacological properties and dosing ranges. Their strengths cannot be compared simply by the number of milligrams.

Does tadalafil always last 36 hours?

No. Tadalafil may remain effective for up to approximately 36 hours, but individual responses vary.

Does sildenafil work better on an empty stomach?

A large or high-fat meal may delay sildenafil’s onset. Taking it on an empty stomach may therefore affect how quickly its effects begin, although individual responses vary.

Can both medicines cause headaches?

Yes. Headache is a recognised potential side effect of both sildenafil and tadalafil.

Are sildenafil and tadalafil available legally in the UK?

Yes. Certain sildenafil and tadalafil medicines are authorised in the United Kingdom. Depending on the specific product, they may require a prescription or an appropriate pharmacy assessment.

Can someone switch between sildenafil and tadalafil?

A healthcare professional may consider changing treatment when clinically appropriate. Switching should take account of the medicines’ different durations of action, interactions and individual health circumstances.