Sildenafil, the active ingredient in Viagra, was first licensed to treat erectile dysfunction (ED) in 1998.1 Since then, several more licensed options have arrived in the UK. That's good news, but it also makes finding the best erectile dysfunction treatment for you a bit more confusing.
This guide walks through how ED tablets work, how the main options differ, and what's worth weighing up before you choose. No jargon, just the stuff that helps you decide.
Every licensed ED tablet works in a similar way. The real differences are how quickly you take it before sex and how long it keeps working.
How do erectile dysfunction treatments work?
When you're aroused, your body releases a chemical called nitric oxide in the penis. This raises the level of another substance, cGMP, which relaxes the smooth muscle in the blood vessels there.2 Relaxed muscle lets more blood flow in, and that's what creates an erection.
Once arousal fades, an enzyme called PDE-5 breaks cGMP down. Blood flow drops and the penis softens again.
Most ED tablets are PDE-5 inhibitors. They block that enzyme, so cGMP sticks around for longer. The result is an erection that's firmer and easier to keep.2
One myth worth busting: these tablets don't make you feel more turned on. You still need sexual stimulation for them to work.3
Recommended reading: Erectile dysfunction: everything you need to know
Think of ED tablets as helping the plumbing, not the mood. Desire and arousal still need to come from you.
Which erectile dysfunction treatments are available?
We prescribe four types of oral ED medication, each named after its active ingredient: sildenafil, tadalafil, vardenafil and avanafil. Most come in a branded version and a generic version.
Generic medicines contain the same active ingredient and work in exactly the same way. They still have to be licensed by the Medicines and Healthcare products Regulatory Agency (MHRA) before they can be prescribed in the UK.
Sildenafil (generic Viagra)
Sildenafil is the active ingredient in Viagra and Viagra Connect. You take it about an hour before sex, and a heavy meal can delay when it starts working.3
It keeps working for around 4 hours, so it suits sex you plan in advance.4 It comes in 25mg, 50mg and 100mg strengths. 50mg is the usual starting dose, and a prescriber can move you up or down depending on how it works for you.3
Viagra Connect
Viagra Connect contains 50mg of sildenafil. In 2017, the MHRA reclassified it as a pharmacy medicine, so you can get it without a prescription after a medical assessment with a pharmacist.5
Tadalafil (generic Cialis)
Tadalafil is the active ingredient in Cialis and Cialis Together. Its big selling point is staying power. One tablet can keep working for up to 36 hours.6
It comes in two forms:6
- On demand (10mg and 20mg) - taken at least 30 minutes before sex, like sildenafil.
- Daily (2.5mg and 5mg) - a lower dose taken every day, so there's always some in your system.
That makes tadalafil a good fit if you have sex often, or you'd rather not plan around a tablet.
Cialis Together
Cialis Together contains 10mg of tadalafil. The MHRA reclassified it as a pharmacy medicine in 2023, with a limit of one tablet a day.7 It isn't sold to men with severe heart problems, severe kidney or liver failure, or men taking certain other medicines. They need treatment supervised by a doctor instead.7
Vardenafil (generic Levitra)
Vardenafil is the active ingredient in Levitra. You take it about 25 to 60 minutes before sex. As with sildenafil, a high-fat meal can slow it down.8
Spedra (avanafil)
Spedra contains avanafil. At the 100mg and 200mg strengths, you take it around 15 to 30 minutes before sex, which is closer to the moment than the other tablets.9 That can suit you if you don't tend to plan ahead.
| Treatment |
Active ingredient |
When to take it |
Generic available? |
| Viagra |
Sildenafil |
About 1 hour before sex |
Yes |
| Cialis |
Tadalafil |
At least 30 minutes before sex, or daily |
Yes |
| Levitra |
Vardenafil |
25 to 60 minutes before sex |
Yes |
| Spedra |
Avanafil |
15 to 30 minutes before sex |
No |
Still not sure? Our ED trial pack includes a mix of treatments at their starting doses, so you can compare them for yourself.
A planned date night or a relaxed weekend away? Matching the tablet to how you actually have sex is often the simplest way to choose.
Are there ED treatments that aren't tablets?
Yes. Tablets are usually the first thing people try, but they're not the only option.
Vacuum pumps
A vacuum pump, such as the VaxAid Deluxe, is a tube you place over your penis. It creates a vacuum that draws blood in to produce an erection.10 It's drug-free, so it can be an option if ED tablets aren't suitable for you.
Alprostadil
Alprostadil is a licensed medicine that comes as an injection or a cream rather than a tablet. It's usually prescribed by a GP or specialist if tablets haven't worked.10
Unlicensed products
Be wary of "herbal" ED products and anything sold online without a health check. The MHRA regularly seizes illegal ED medicines bought online, and their contents can't be trusted.11 It's worth understanding the physical causes of ED and speaking to our pharmacy team or your GP instead.
Do not buy ED medicine from a website that does not ask about your health first. You cannot be sure what an unlicensed product contains.
How do you choose the best erectile dysfunction treatment?
There's no single best ED tablet for everyone. Sildenafil and tadalafil are the two you'll hear about most, but the right one comes down to you. Here's what actually sets them apart.
How often you have sex
Planned, occasional sex? A shorter-acting tablet like sildenafil may be all you need. Sex more often, or more spontaneously? Tadalafil's longer window, or a daily dose, could suit you better.6
How soon you want it to work
If you'd rather not take a tablet an hour in advance, Spedra is taken closer to the time.9
Dose strength
A dose that's too high makes side effects more likely. Too low, and it might not do the job. Your prescriber will usually start you on the standard dose and adjust from there.3
Branded or generic
Branded and generic versions of the same medicine contain the same active ingredient and work the same way. Generics just tend to cost less.
Your health and other medicines
ED tablets aren't safe for everyone. You must not take them if you use nitrate medicines (often prescribed for chest pain) or recreational "poppers", as the combination can cause a dangerous drop in blood pressure.3 Your prescriber will check your health and any other medicines before recommending a treatment.
Recommended reading: Sildenafil vs tadalafil: which is right for you?
Never take an ED tablet if you use nitrates or poppers. Always tell your prescriber about every medicine you take.
What are the side effects of ED treatments?
Like all medicines, ED tablets can cause side effects. They're usually mild and short-lived, and plenty of men don't get any at all. The most common include:
- Headache - very common with sildenafil, affecting more than 1 in 10 men.3
- Flushing - common; a warm, red face or neck.
- Indigestion - common.
- Blocked or runny nose - common.
- Dizziness - common.
- Changes to your vision - such as a blue tinge to things, which is common with sildenafil.3
- Back pain and aching muscles - common with tadalafil.6
Always read the patient information leaflet that comes with your medicine. If side effects bother you or don't settle, speak to a prescriber, as a different dose or treatment may suit you better.
Some side effects need urgent help. Contact a doctor straightaway if you have an erection lasting more than 4 hours, chest pain, or a sudden loss of sight or hearing.3
An erection that won't go down after 4 hours, or a sudden change to your sight or hearing, is a medical emergency. Do not wait to see if it passes.
When should you speak to a GP about ED?
ED is common, and it's nothing to be embarrassed about. But it can sometimes be an early sign of another health condition, such as heart disease, high blood pressure or diabetes.10
Book a GP appointment if:
- ED tablets haven't helped after several tries at the right dose
- Your ED came on suddenly or alongside other new symptoms
- You have a heart condition or take medicines that could interact with ED treatment
- You're worried about what might be causing it
Frequently asked questions
How long does Viagra last?
Viagra usually keeps working for around 4 hours after you take it. That doesn’t mean a 4-hour erection. It means you’ll find it easier to get an erection when you’re aroused during that window. A heavy meal can delay when it starts working. If an erection lasts more than 4 hours, get medical help straightaway.
How long does Cialis last?
One Cialis tablet can keep working for up to 36 hours, which is why some people call it the weekend pill. You still need to be aroused to get an erection during that time. There’s also a lower daily dose of tadalafil, taken every day, so you don’t need to plan sex around a tablet.
Can you take Cialis and Viagra together?
No. You should not take two ED medicines at the same time. Combining them raises the risk of side effects, including a drop in blood pressure. If your current treatment isn’t working well enough, speak to a prescriber. They may suggest a different dose or switching to another medicine instead.
Can you take tadalafil daily?
Yes. Tadalafil comes in low doses of 2.5mg and 5mg that are designed to be taken once a day, at around the same time. This keeps a steady level in your body, so you can have sex whenever the moment’s right. It tends to suit men who have sex at least twice a week.
Cialis Together is a 10mg tadalafil tablet you can buy without a prescription after a consultation with a pharmacist. It works in the same way as Cialis and can last up to 36 hours. It isn’t suitable for men with severe heart problems, severe kidney or liver failure, or those taking certain medicines.
References
- Pharmaceutical Journal. Three decades of Viagra. Pharmaceutical Journal. 2025. pharmaceutical-journal.com
- Corbin JD, Francis SH. Cyclic GMP phosphodiesterase-5: target of sildenafil. Journal of Biological Chemistry. 1999;274(20):13729-13732. doi:10.1074/jbc.274.20.13729
- Viatris. Viagra 50 mg film-coated tablets: Summary of Product Characteristics. Electronic Medicines Compendium; 2025. medicines.org.uk/emc
- NHS. Sildenafil (Viagra). NHS website; 2026. nhs.uk
- Medicines and Healthcare products Regulatory Agency. MHRA reclassifies Viagra Connect tablets to a Pharmacy medicine. GOV.UK; 2017. gov.uk
- NHS. Tadalafil. NHS website; 2026. nhs.uk
- Medicines and Healthcare products Regulatory Agency. MHRA reclassifies Cialis Together tablets to a Pharmacy medicine. GOV.UK; 2023. gov.uk
- European Medicines Agency. Levitra (vardenafil): EPAR summary for the public. European Medicines Agency; 2016. ema.europa.eu
- A. Menarini Farmaceutica Internazionale. Spedra 100 mg tablets: Summary of Product Characteristics. Electronic Medicines Compendium; 2024. medicines.org.uk/emc
- NHS. Erectile dysfunction (impotence). NHS website; 2026. nhs.uk
- Medicines and Healthcare products Regulatory Agency. 20 million illegal erectile dysfunction pills seized as MHRA warns against risky online buys. GOV.UK; 2026. gov.uk
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.