Sildenafil vs Tadalafil: Which ED Tablet Is Right for You?
Sildenafil (Viagra) and tadalafil (Cialis) are the UK's two most prescribed erectile dysfunction treatments. Both belong to the same drug class, both work well, and both are available as affordable generics. But they are not interchangeable — the differences in duration, food interaction, dosing options, and side effect profile mean one will suit your lifestyle significantly better than the other. This guide compares them directly so you and your prescriber can make the right call.
Both medications are available through Access Doctor's online sildenafil and tadalafil prescription service, reviewed by GPhC-registered pharmacist independent prescribers following a confidential consultation.
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Order Sildenafil or Tadalafil → ✓ GPhC-registered pharmacy #9011198 ✓ Pharmacist independent prescribers ✓ Discreet next-day deliveryWhat Are Sildenafil and Tadalafil?
Both sildenafil and tadalafil are PDE5 inhibitors (phosphodiesterase type 5 inhibitors). They work by blocking the PDE5 enzyme, which ordinarily restricts blood flow to the penis. By inhibiting it, both drugs allow smooth muscle in the penile vasculature to relax and blood vessels to widen — increasing blood flow and enabling an erection in response to sexual arousal. Neither drug causes an automatic erection. Sexual stimulation is always required.
For a broader understanding of how PDE5 inhibitors work within the context of erectile dysfunction, our guide to ED basics explains the physiology clearly. If you are considering sildenafil specifically for the first time, our dedicated guide to what Viagra (sildenafil) is and how it works and our complete sildenafil UK guide cover the medication in depth.
Sildenafil (Viagra)
Sildenafil has been available since 1998 — originally developed by Pfizer as Viagra, it is one of the most widely studied medicines in history. Generic sildenafil became available at a fraction of the branded cost after patent expiry, making it highly accessible. It comes in 25mg, 50mg, and 100mg tablets. Our sildenafil dosage and side effects guide covers which strength to start with and what to expect.
Tadalafil (Cialis)
Tadalafil was introduced in 2003 by Eli Lilly as Cialis, rapidly gaining popularity for its significantly longer duration of action — earning it the nickname "the weekend pill." Generic tadalafil has been available since 2017. It comes in 2.5mg, 5mg, 10mg, and 20mg doses, with a daily low-dose option that no other ED medication offers.
Clinical Insight — Dr Abdishakur M Ali: The first question I ask a man who comes to me for an ED prescription is not which drug he has heard of — it is what his sex life actually looks like. How often does he have sex? Does he usually know in advance or does it tend to be spontaneous? Does he eat a large meal in the evening? Is he on any medications I need to check? The answers to those practical questions almost always determine the right prescription before we even get to the pharmacology. Sildenafil for the man who plans ahead; tadalafil for the man who values spontaneity or has sex regularly enough that on-demand dosing feels disruptive.
Quick Comparison: Sildenafil vs Tadalafil
| Feature | Sildenafil (Viagra) | Tadalafil (Cialis) |
|---|---|---|
| Brand name | Viagra | Cialis |
| Drug class | PDE5 inhibitor | PDE5 inhibitor |
| How fast it works | 30–60 minutes | 30–60 minutes |
| How long it lasts | 4–6 hours | Up to 36 hours |
| Affected by food? | Yes — fatty meals delay effect | No — works with or without food |
| Available doses | 25mg, 50mg, 100mg | 2.5mg, 5mg, 10mg, 20mg |
| Daily use option? | No | ✓ Yes (2.5mg or 5mg daily) |
| Taken as needed? | ✓ Yes | ✓ Yes (10mg or 20mg) |
| Distinctive side effect | Temporary visual disturbances (blue tinge) | Back pain and muscle aches |
| Generic available? | ✓ Yes | ✓ Yes |
| Available at Access Doctor? | ✓ Yes | ✓ Yes |
How Long Does Each One Last?
This is the most clinically meaningful practical difference between the two drugs — and usually the deciding factor for most men.
How Long Does Sildenafil (Viagra) Last?
Sildenafil typically lasts 4 to 6 hours, with peak effectiveness reached around 1–2 hours after taking it. It suits planned sexual activity well. Once the window closes, a further dose cannot be taken within 24 hours.
Food interaction: Taking sildenafil after a large or high-fat meal can delay absorption by up to an hour and reduce peak plasma concentration. For most reliable results, take it on an empty stomach or after a light meal. Our guide to what to expect when taking Viagra for the first time explains how to time your dose correctly.
How Long Does Tadalafil (Cialis) Last?
Tadalafil lasts significantly longer — up to 36 hours from a standard as-needed dose. Its effectiveness is not meaningfully affected by food or alcohol within normal limits. It can also be taken as a daily low dose (2.5mg or 5mg) to maintain a continuous background level, removing the need to time doses around sex entirely.
How Quickly Do They Work?
Both begin working within 30 to 60 minutes for most men. Tadalafil may act slightly faster in some cases as food does not slow its absorption. Most prescribers recommend taking either tablet approximately one hour before anticipated sexual activity — though some men find both work within 30 minutes on an empty stomach.
Dosage Guide
Sildenafil Dosage
- Starting dose: 50mg — taken approximately one hour before sex, on an empty stomach if possible
- Increased to 100mg if the 50mg dose is insufficient
- Reduced to 25mg if side effects occur at 50mg
- No more than once every 24 hours
- Do not crush or split tablets — swallow whole with water
Tadalafil Dosage
- As-needed: 10mg, taken at least 30 minutes before sex — with or without food
- Increased to 20mg if 10mg is insufficient
- Daily dose: 2.5mg or 5mg — taken at the same time each day, regardless of sexual activity
- No more than one dose in any 24-hour period (as-needed regimen)
- Daily dosing is better value for men who have sex more than twice a week
Not Sure Which to Choose? Let a Prescriber Advise You
Our pharmacist independent prescribers discuss your lifestyle, medical history, and preferences before recommending the most appropriate sildenafil or tadalafil option — including daily tadalafil if relevant.
Get Your Prescription Online → ✓ GPhC-registered pharmacy #9011198 ✓ Confidential online consultation ✓ Discreet next-day deliverySide Effects: Sildenafil vs Tadalafil
Common to Both
- Headache — the most frequently reported side effect of both
- Facial flushing and warmth
- Nasal congestion or runny nose
- Indigestion or mild stomach discomfort
- Dizziness — particularly if combined with alcohol
More Common with Sildenafil
- Visual disturbances — temporary blue-tinted or blurred vision caused by mild effect on PDE6 in the retina. Generally harmless, short-lived (under an hour), and dose-dependent. More common at 100mg.
- More pronounced facial flushing, particularly at higher doses
More Common with Tadalafil
- Back pain and muscle aches (myalgia) — typically appearing 12–24 hours after the dose and resolving within 48 hours. Related to the longer systemic presence of tadalafil and smooth muscle relaxation beyond the genitourinary system. Often resolves with dose reduction.
- Limb pain
Clinical Insight — Dr Abdishakur M Ali: The visual side effect of sildenafil — that transient blue tinge or sensitivity to light some men notice — frequently causes unnecessary alarm when it hasn't been flagged in advance. It is medically benign in almost all cases and resolves within an hour. I now mention it routinely as part of prescribing counselling, because a man who experiences it unexpectedly may stop the medication thinking something is seriously wrong, and then never try it again. It is worth noting: if vision changes are persistent, severe, or accompanied by pain, that warrants urgent review — but brief and transient visual effects at therapeutic doses are documented and expected.
Critical safety warning: Do not take sildenafil or tadalafil with nitrate medications (glyceryl trinitrate spray, isosorbide mononitrate, isosorbide dinitrate — prescribed for angina or chest pain). The combination can cause a catastrophic and potentially fatal drop in blood pressure. Always disclose every medication you take during your online consultation.
Are Sildenafil and Tadalafil Equally Effective?
In clinical terms, yes. A systematic review analysing 16 clinical trials found no statistically significant difference in overall efficacy between sildenafil and tadalafil for treating ED. Both produce meaningful improvement in erectile function scores versus placebo. Head-to-head trial data consistently shows comparable success rates — approximately 81–82% for both.
Where tadalafil tends to score higher is in patient and partner satisfaction studies, driven almost entirely by its 36-hour window rather than any pharmacological superiority. Some men, however, find sildenafil produces a more predictable, sharper response for them personally. Individual variation is real and matters clinically — which is why trying both (sequentially, not simultaneously) remains a legitimate approach when the first choice doesn't fully satisfy.
Clinical Insight — Dr Abdishakur M Ali: I always tell patients that the best ED medication is the one they will actually use correctly. That sounds obvious, but it has real consequences. A man who finds the timing pressure of sildenafil creates anxiety — watching the clock, worrying whether the window has passed — will get worse outcomes than a man on tadalafil who has taken his dose and can relax. Conversely, a man who dislikes having any drug continuously in his system, or who has sex infrequently, gets no benefit from daily tadalafil. The pharmacology is similar enough that the right choice is almost always the lifestyle fit, not the drug itself.
Cost in the UK
Since the Viagra patent expired in 2013 and Cialis in 2017, affordable generic versions of both medications are widely available. Generic sildenafil is typically the most affordable option for occasional use. For men who have sex frequently, daily low-dose tadalafil (2.5mg or 5mg) is often more cost-effective than buying higher-strength as-needed tablets multiple times per week.
Both are available at competitive prices through Access Doctor's online prescription service for sildenafil and tadalafil.
Which Is Right for Me — Sildenafil or Tadalafil?
Choose Sildenafil if you…
- Are comfortable planning sex around a dose
- Have sex occasionally rather than frequently
- Want the most thoroughly studied ED medication
- Previously tried tadalafil and found the back pain problematic
- Want the most affordable option for occasional use
- Prefer a shorter-acting drug so effects aren't felt for 36 hours
Choose Tadalafil if you…
- Value spontaneity — no timing pressure around doses
- Don't want food to affect how well the medication works
- Have sex regularly (twice or more per week)
- Found sildenafil's 4–6 hour window too short or its food interaction inconvenient
- Want the option of a daily pill for continuous background effectiveness
For a detailed look at how all four MHRA-licensed ED medications compare — including vardenafil and avanafil — our Viagra vs Cialis vs Levitra comparison guide covers the full picture.
Can You Switch Between Sildenafil and Tadalafil?
Yes — straightforwardly. If you have tried one and it doesn't suit you — whether due to side effects, duration, or a lifestyle change — switching to the other is a simple prescribing decision. Inform your prescriber and they can issue a new prescription. Do not take both on the same day. Our guide to whether ED treatment is guaranteed to work sets honest expectations about what to anticipate when switching.
Who Should Not Take Sildenafil or Tadalafil?
PDE5 inhibitors are not suitable for everyone. Do not take either medication if you:
- Take nitrate medications for chest pain or heart conditions (GTN spray, isosorbide mononitrate, isosorbide dinitrate) — this combination is absolutely contraindicated and potentially fatal
- Take alpha-blockers for blood pressure or prostate problems without your prescriber's knowledge — dose adjustment may be needed
- Have been advised to avoid sexual activity due to a cardiac condition
- Have severe liver or kidney disease
- Have had a recent stroke or heart attack (within the last three months)
- Have low blood pressure (hypotension)
- Are taking ritonavir or other strong CYP3A4 inhibitors — these significantly increase drug levels and dose reduction is required
Our guide to what causes erectile dysfunction is useful background if you suspect an underlying condition — such as cardiovascular disease or hypogonadism — may be driving your ED and need addressing alongside medication. For younger men specifically, our guide to ED in young men covers the different risk profile and treatment considerations that apply under 40.
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Sildenafil (Generic Viagra)
MHRA-licensed. Works in 30–60 minutes. Effective for 4–6 hours. The UK's most widely prescribed ED medication. 25mg, 50mg, 100mg.
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36-hour window · daily option
Tadalafil (Generic Cialis)
MHRA-licensed. Effective for up to 36 hours. Daily 5mg option available. Not affected by food. 2.5mg, 5mg, 10mg, 20mg.
Order licensed tadalafil →Ready to Start ED Treatment?
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Start Free Consultation → ✓ GPhC-registered pharmacy #9011198 ✓ Pharmacist independent prescribers ✓ Discreet next-day deliveryMedical disclaimer: This article is for informational purposes only and does not constitute medical advice. Sildenafil and tadalafil are prescription-only medicines in the UK. Always complete a clinical consultation before use. All prescriptions issued through Access Doctor are provided by GPhC-registered pharmacist independent prescribers following a clinical assessment. If you are concerned about symptoms or interactions, consult your GP or call NHS 111.
Frequently Asked Questions
Is tadalafil stronger than sildenafil?
Not necessarily. Both are highly effective PDE5 inhibitors with near-identical clinical success rates (around 81–82%). Tadalafil lasts significantly longer — up to 36 hours vs 4–6 hours — but this is a duration advantage, not a potency advantage. Individual response varies, and some men find sildenafil produces a stronger effect for them personally.
Can I take sildenafil and tadalafil together?
No — never take both on the same day. Combining two PDE5 inhibitors produces no additional benefit and significantly increases the risk of dangerous hypotension, priapism (prolonged painful erection), and other serious adverse effects. Use one or the other.
How long does Viagra (sildenafil) last?
Sildenafil typically lasts 4 to 6 hours, with peak effectiveness reached 1–2 hours after taking it. A large, fatty meal taken close to the dose can delay onset and reduce peak effectiveness — take it on an empty stomach or after a light meal for best results.
How long does Cialis (tadalafil) last?
A standard as-needed dose of tadalafil (10mg or 20mg) lasts up to 36 hours. A daily low dose (2.5mg or 5mg) maintains a continuous background level in the system, providing readiness at any time without timing doses around sex. Tadalafil's effectiveness is not significantly affected by food.
Does sildenafil or tadalafil work faster?
Both begin working within 30 to 60 minutes for most men. Tadalafil may act slightly faster in some cases as food does not slow its absorption. Most prescribers recommend taking either tablet around one hour before anticipated sexual activity, though both can work within 30 minutes when taken on an empty stomach.
Can I buy sildenafil or tadalafil online in the UK?
Yes. Both can be prescribed through a confidential online consultation with a UK-registered pharmacist independent prescriber. Access Doctor is a GPhC-registered pharmacy offering both medications, with discreet next-day delivery once your consultation is approved. Always use a GPhC-registered pharmacy — never purchase from unregistered sites.
Which ED tablet is cheapest in the UK?
Generic sildenafil is typically the lowest cost per tablet for occasional use. For men who have sex regularly, daily low-dose tadalafil (2.5mg or 5mg) can be more cost-effective overall than buying higher-strength as-needed tablets multiple times per week.
Does tadalafil work better than sildenafil for severe ED?
Clinical studies have not found a significant difference in efficacy between the two for any severity of ED. Both are NICE first-line treatments. A prescriber can help determine which is more appropriate for your individual circumstances, including any underlying conditions that may be contributing.
References
- NICE. Erectile dysfunction — management. Clinical Knowledge Summary 2023. cks.nice.org.uk
- NHS. Erectile dysfunction (impotence). nhs.uk
- Carson CC et al. Tadalafil, an oral phosphodiesterase type 5 inhibitor, for the treatment of erectile dysfunction. BJU Int. 2004. pubmed.ncbi.nlm.nih.gov
- Hatzimouratidis K et al. EAU guidelines on male sexual dysfunction. European Association of Urology. 2023. uroweb.org
- GPhC. Standards for registered pharmacies. pharmacyregulation.org