Sildenafil vs Tadalafil: treatment duration, dosage and side effects

If you've researched treatment for erectile dysfunction (ED), you will have come across sildenafil and tadalafil. They're the two most commonly prescribed ED medications in the UK and both are proven to be effective.

But there are some key differences between the two that make them suitable for different people. If you're weighing up all your options, our guide to picking the right ED treatment covers the full range. This article focuses specifically on how sildenafil and tadalafil compare.

Both belong to a group of medicines called PDE5 inhibitors. They work by relaxing blood vessels and increasing blood flow to the penis, making it easier to get and maintain an erection when you're sexually aroused.^1,2 But neither one will give you an erection out of the blue or increase your sex drive as many people mistakenly believe.

So, how do they actually differ? Let's break it down.

Sildenafil vs Tadalafil: How Long Do They Last?

This is the biggest difference between the two. Sildenafil typically lasts around four to six hours, with its peak effect about one to two hours after you take it.¹ That makes it well suited to planned sexual activity within a set window.

Tadalafil, on the other hand, can remain active in your system for up to 36 hours.² It's sometimes called the 'weekend pill' because you could take it on a Friday evening and still feel its effects on Sunday morning. This longer window means less pressure to time things precisely and more room for spontaneity.

A 36-hour duration does not mean a 36-hour erection though. It means the medication is active in your body during that window and can help you achieve an erection when you're aroused.

Dosage and How to Take Them

Sildenafil

The recommended starting dose is 50mg, taken around an hour before sexual activity.¹ Your prescriber may adjust this to 25mg or up to 100mg depending on how well it works and whether you experience side effects.

It should be taken no more than once per day. Sildenafil works best on an empty stomach – a heavy or fatty meal can delay its onset.¹

Tadalafil (as needed)

The recommended starting dose is 10mg, taken at least 30 minutes before sexual activity. This can be increased to 20mg if needed.² Like sildenafil, it should not be taken more than once per day.

One advantage is that food does not significantly affect how tadalafil is absorbed, so you don't need to worry about meal timing as much.²

Tadalafil Daily

Tadalafil Daily is a lower-strength option (2.5mg or 5mg) taken once every day at the same time, regardless of when you plan to have sex.³ After about five days it builds up to a steady level in your system, so you're always ready.

This is a popular choice for men who are sexually active more than twice a week and don't want to plan around a tablet.³

Side Effects of Sildenafil and Tadalafil

Because they belong to the same drug class, sildenafil and tadalafil share many of the same potential side effects. These are usually mild and temporary, and tend to ease as your body adjusts. Common symptoms for both include headache, flushing, nasal congestion, and indigestion.^1,2

There's a couple specific symptoms worth knowing about though. Sildenafil can occasionally cause a temporary blue tint to your vision, caused by a mild effect on a related enzyme (PDE6) in the eye.¹ Tadalafil is more commonly associated with back pain and muscle aches, which typically appear 12 to 24 hours after taking it and should resolve within 48 hours.²

One thing to keep in mind. As tadalafil stays in your system longer, any side effects you do experience may last longer too. If side effects are a concern, sildenafil's shorter duration means they'll pass more quickly.

Which Is More Effective for Erectile Dysfunction (ED)?

Both are effective treatments. A systematic review and meta-analysis published in International Urology and Nephrology, which analysed 16 head-to-head trials involving over 5,000 patients, found no significant difference in overall efficacy between sildenafil and tadalafil.⁴ Both improved erection quality and successful intercourse rates to a similar degree.

The same study did find that patients and their partners tended to prefer tadalafil, largely because of its longer duration and the flexibility it allows.⁴ A separate crossover trial of PDE5-inhibitor-naive men found that around 69% chose tadalafil as their preferred treatment after trying both, with the most commonly cited reason being the ability to get an erection well after taking the tablet.⁵

That said, preference doesn't necessarily mean tadalafil is better. Many men prefer sildenafil for its shorter window of action and predictability.

If you're unsure which will suit you, our ED Trial Pack lets you try both so you can compare them firsthand.

How to Choose Between Sildenafil and Tadalafil

The right choice mainly comes down to your routine, how often you think you'll need the treatment, and what you value most.

Sildenafil might suit you better if you prefer a treatment that's active for a defined window, you have sex on a relatively predictable schedule, you want a well-established medication with decades of clinical data behind it, or you'd rather any side effects clear your system quickly.

Tadalafil (as needed) might suit you better if you value spontaneity and don't want to time a pill precisely, you prefer a wider window of effectiveness, or you regularly eat before sexual activity (since food doesn't affect tadalafil's absorption).²

Tadalafil Daily might suit you better if you're sexually active more than twice a week, you want to be ready at any time without taking a tablet beforehand, or you prefer the routine of taking a pill everyday rather than when you need it.³

Tips for Getting the Best Results from Your ED Medication

Whichever treatment you choose, taking some practical steps can help it work as well as possible.

If you're taking sildenafil, try to take it on an empty stomach or after a light meal. A large, fatty meal can delay absorption by up to an hour, which can be frustrating if you've carefully timed your dose.¹

Give the medication enough time to work. Both sildenafil and tadalafil are generally recommended to be taken around 30 to 60 minutes before sex, though individual response varies.^1,2 For instance, Tadalafil can take up to two hours to reach full effect for some men.

Alcohol in moderation is fine, but heavy drinking can reduce the effectiveness of both medications and increase the likelihood of side effects like dizziness or flushing.

Safety Information You Should Know

Both sildenafil and tadalafil are prescription-only medicines in the UK (with the exception of Viagra Connect and Cialis Together which can be purchased over-the-counter).⁶

They should not be taken together, and you must not take either medication with nitrate-based medicines such as glyceryl trinitrate or isosorbide mononitrate, as the combination can cause a dangerous drop in blood pressure.^1,2

You should also tell your prescriber about any other medications you're taking, particularly alpha-blockers, certain antifungals or HIV protease inhibitors, as these can interact with PDE5 inhibitors.^1,2

If you experience an erection lasting more than four hours (priapism), sudden loss of vision or a sudden decrease in hearing, stop taking the medication and seek medical attention straight away.^1,2

Making Your Choice

Sildenafil and tadalafil are both effective and well-tolerated treatments for erectile dysfunction. Neither is objectively better than the other – the right one depends on how you want treatment to fit into your life. For a comparison using the brand names, see our Cialis vs Viagra guide.

If you value a defined, shorter-acting treatment, sildenafil is a solid choice. If you want longer-lasting flexibility, tadalafil may be the better fit.

Frequently Asked Questions

Is tadalafil stronger than sildenafil?

Not exactly. They have their own dosage scales and contain different active ingredients so they are not directly comparable. Considering one as stronger or weaker isn't technically accurate.

For instance, the maximum dose of tadalafil is 20mg, while sildenafil is 100mg. These doses aren't equivalent to each other despite both being maximum doses of ED medication, so neither is stronger or weaker than the other.

Both treatments have achieved similar clinical outcomes⁴, so the question is which suits your lifestyle and needs better.

Can I switch from sildenafil to tadalafil (or vice versa)?

Yes, you can switch between them. You should not take both on the same day. If you're moving from one to the other, stop taking the first and begin the second at the next appropriate time. Your prescriber can advise on the best approach.

How long does sildenafil take to work?

Sildenafil typically starts working within 30 to 60 minutes. Taking it on an empty stomach usually helps it work faster. Its effects generally last four to six hours.¹

How long does tadalafil last?

An as-needed dose of tadalafil can last up to 36 hours.² This doesn't mean a continuous erection for that long. It means the medication remains active in your system and can support an erection when you're sexually stimulated during that time.

Can I take sildenafil or tadalafil with food?

Tadalafil can be taken with or without food.² Sildenafil works best on an empty stomach or after a light meal. High-fat foods can delay its absorption, meaning the effects take longer to start.¹

Are there any medications I should avoid while taking these?

Yes. Both sildenafil and tadalafil must not be taken with nitrate medications (prescribed for chest pain) due to the risk of a severe drop in blood pressure.^1,2 Always disclose your full medication list during your consultation.

Can I buy sildenafil or tadalafil without a prescription in the UK?

Viagra Connect (sildenafil 50mg) and Cialis Together (tadalafil 10mg) are available without a prescription after a pharmacist consultation.⁶ Our Cialis Together vs tadalafil guide covers the tadalafil option in more detail.

References

1. Sildenafil 50mg film-coated tablets – Summary of Product Characteristics (SmPC). Electronic Medicines Compendium (EMC). Available at: medicines.org.uk/emc/product/7141/smpc
2. Tadalafil 20mg film-coated tablets – Summary of Product Characteristics (SmPC). Electronic Medicines Compendium (EMC). Available at: medicines.org.uk/emc/product/9363/smpc
3. Tadalafil 5mg film-coated tablets – Summary of Product Characteristics (SmPC). Electronic Medicines Compendium (EMC). Available at: medicines.org.uk/emc/product/10231/smpc
4. Gong B, Ma M, Xie W, et al. Direct comparison of tadalafil with sildenafil for the treatment of erectile dysfunction: a systematic review and meta-analysis. Int Urol Nephrol. 2017;49(10):1731–1740. PMID: 28741090.
5. Bai WJ, Li HJ, Dai YT, et al. An open-label, multicenter, randomized, crossover study comparing sildenafil citrate and tadalafil for treating erectile dysfunction in Chinese men naïve to phosphodiesterase 5 inhibitor therapy. Asian J Androl. 2015;17(1):61–67. PMID: 25370206.
6. Viagra Connect 50mg film-coated tablets – Summary of Product Characteristics (SmPC). Electronic Medicines Compendium (EMC). Available at: https://www.medicines.org.uk/emc/files/pil.8725.pdf

This article is intended for informational purposes only and does not replace professional medical advice. Always read the patient information leaflet supplied with your medication and speak to a healthcare professional if you have specific concerns.

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