Tadalafil vs Viagra: Duration, Dosing and Key Differences

Sildenafil is the active ingredient in Viagra, and tadalafil is the active ingredient in Cialis. Both are PDE5 inhibitors commonly prescribed for erectile dysfunction, and where they differ most is in how long they work.

Tadalafil can remain active for up to 36 hours, while sildenafil usually lasts around four hours. Dosing differs too: tadalafil comes both on demand and as a once-daily option, while sildenafil is taken on demand. Food sensitivity, side effects and formulations also vary.

Neither is better in a general sense. The right choice depends on how often you need treatment, your routine, your preferences and your health, which is why this comparison is best used alongside guidance from a UK registered prescriber.

What Is the Real Difference?

Both are phosphodiesterase type 5 inhibitors, and both work by increasing blood flow to the penis in response to sexual stimulation. Neither creates an erection without stimulation, and both are prescription treatments for erectile dysfunction.

Their overall effectiveness is similar, so the genuine differences are practical: how long each stays active, how they are dosed, how sensitive each is to food, and what formulations exist. Those differences can matter a lot depending on your routine, which is why both remain available rather than one replacing the other.

How They Work

During arousal, a signalling chemical relaxes the blood vessels in the penis so blood can flow in. An enzyme called PDE5 normally breaks that signal down again, allowing things to return to normal afterwards.

Both sildenafil and tadalafil inhibit PDE5, so the signal lasts longer and blood flow increases during sexual stimulation.

Because they belong to the same class, they share some side effects, although their individual profiles differ.

Duration: How Long Each One Lasts

Tadalafil: Up to 36 Hours

Tadalafil's effect can last up to 36 hours after a single on-demand dose, considerably longer than other options in its class.

That does not mean a continuous effect throughout. Stimulation is still required. It means the medicine remains active in the body and available to respond for longer. Peak levels in the blood are reached at about two hours.

Sildenafil: Around Four Hours

Sildenafil has a much shorter duration, so timing around sexual activity generally matters more.

The difference comes down to half-life, the time it takes the body to clear half of a dose. Tadalafil's longer half-life is the main reason it lasts longer.

It is also why tadalafil can be taken once daily at a low dose to maintain a steady background level, an approach that would not work as well with a medicine the body clears much faster.

Sildenafil may suit people who prefer a shorter treatment window around a particular occasion.

Dosing: How Each One Is Taken

Tadalafil

Tadalafil can be prescribed in two patterns.

For on-demand tadalafil, the usual starting dose is 10mg, which may be increased to 20mg, taken at least 30 minutes before anticipated activity.

Once-daily tadalafil, at 5mg or 2.5mg, may be considered for people who expect to need treatment frequently, such as at least twice a week.

Sildenafil

Sildenafil is taken on demand rather than daily, usually about an hour before anticipated activity. The starting dose is 50mg, which a prescriber may adjust between 25mg and 100mg.

There is no licensed once-daily sildenafil regimen for erectile dysfunction.

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Does Food Affect Either One?

Only one of them. Tadalafil's absorption is not significantly affected by food, so it can be taken with or without a meal.

Sildenafil's absorption can be delayed by a fatty meal, so it may take longer to start working if taken shortly after eating.

This is one of the more practical differences for everyday use, since it affects how much planning each option needs around meals.

Is There a Dissolvable Version?

For sildenafil, yes. A licensed sildenafil 50mg orodispersible film is available in the UK. It dissolves on the tongue rather than being swallowed with water, and works in the same way as the standard tablet.

For tadalafil, no. There is currently no UK-licensed dissolvable version, and tadalafil is available only as a film-coated tablet. A product offered as dissolvable tadalafil is a red flag rather than a genuine option.

Getting Tadalafil or Sildenafil in the UK

Both require an assessment, though not always the same type.

Standard tadalafil and sildenafil are prescription-only medicines, so a UK registered prescriber assesses suitability before either is supplied, online or in person.

Some products in each class are pharmacy medicines instead: Viagra Connect for sildenafil, and Cialis Together for tadalafil. These can be supplied after a pharmacist's assessment, and the underlying safety questions are similar either way.

Whichever route applies, the assessment is not a formality. It is how suitability is established, covering your medical history, current medicines and possible interactions.

Adding Vardenafil to the Comparison

Bringing vardenafil, sold as Levitra, into the comparison shows that duration and food sensitivity vary across the whole class, not just between two options.

Vardenafil should be avoided in people with congenital QT prolongation, or taking certain medicines that affect heart rhythm.

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How the Side Effects Compare

Both share several mild side effects, because they act on the same pathway: headache, flushing and indigestion. Both can also lower blood pressure to some degree, depending on the medicine, dose and individual.

Tadalafil is more specifically linked to back pain, muscle aches and nasal congestion.

Sildenafil is more associated with visual disturbances, such as a mild blue tinge to vision or temporary blurring, particularly at higher doses. That comes from its effect on a related enzyme in the eye, and is separate from the sudden, serious vision loss that always needs urgent attention.

Neither profile is straightforwardly safer. They differ in which mild effects are more commonly reported, and for most people those effects are mild. A prescriber can help weigh this up if a particular side effect concerns you.

Which One Might Suit You Better?

That depends on how often you need treatment, timing, your routine and your preference, not on which is more effective.

People who prefer a shorter window may value sildenafil. People who want more flexibility around timing may value tadalafil. Food sensitivity and individual side effects can also make one genuinely more comfortable than the other.

None of these are reasons to decide without an assessment. A prescriber can talk through which factors matter most to you, and confirm which options are suitable given your health.

Who Should Not Take Either

Nitrates: An Absolute No

Neither tadalafil nor sildenafil should ever be taken by anyone using a nitrate medicine, in any form, including nitrates for chest pain and recreational nitrites such as amyl nitrite. The combination can cause a potentially dangerous fall in blood pressure.

Other Interactions

Tell your prescriber about all the medicines you take, including supplements and anything bought without a prescription, particularly:

• Alpha blockers and some other blood pressure medicines, since combining them with either medicine can lower blood pressure further
• Other PDE5 inhibitors, which should not be combined with tadalafil or sildenafil unless a prescriber specifically directs it
• Medicines affecting liver enzymes, including some antibiotics and antifungals, which can change how much of either medicine builds up in the body

Heart disease also needs assessing before either is prescribed.

Medical Disclaimer

This article is for general information only and does not replace individual medical advice. Tadalafil and sildenafil are prescription medicines, apart from the specific pharmacy products mentioned above, and suitability depends on an individual clinical assessment.

These treatments may support erectile function, but they do not cure the underlying causes. Results and side effects vary between individuals.

If you experience sudden vision or hearing loss, chest pain, an erection lasting more than four hours, or another serious symptom, seek urgent medical attention.

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