Cialis or Viagra: which is right for you?
Erectile dysfunction (ED) is one of the most common conditions men discuss with a doctor, and two medicines dominate the conversation: Cialis (tadalafil) and Viagra (sildenafil). Both are approved by the European Medicines Agency (EMA). Both belong to the same class of medicines — phosphodiesterase type 5 (PDE5) inhibitors. Both work, for the same fundamental reason.
So why are there two, and does it matter which one you use? It does. The differences between tadalafil and sildenafil are clinically meaningful, and the right choice depends on how — and how often — you want to use the medicine.
This article compares Cialis and Viagra on the factors that actually affect everyday use: how long each lasts, how quickly each works, how food and alcohol affect them, their side-effect profiles, their approved uses beyond ED, and their cost. It reflects the EMA-approved product information and published clinical evidence. It is informational, not a prescription — which medicine, if either, is appropriate for you is a decision only an independent doctor can make after reviewing your health. To look at a specific medicine route, see the Cialis (tadalafil) treatment page or the Viagra (sildenafil) treatment page.
How they work (and why they are so similar)
Both tadalafil and sildenafil are PDE5 inhibitors. During sexual stimulation, the body releases nitric oxide in the erectile tissue, which triggers production of a signalling molecule called cGMP. cGMP relaxes the smooth muscle in the blood vessels of the penis, allowing blood to flow in and produce an erection.
In men with ED, an enzyme called PDE5 breaks down cGMP too quickly, undermining this process. Both Cialis and Viagra block PDE5, allowing cGMP to persist for longer and supporting a normal erectile response to sexual stimulation.
A point that is often misunderstood: neither medicine produces an erection without sexual stimulation. They support the body's natural response; they do not replace it.
Because the mechanism is essentially the same, the two medicines share most of their side effects and contraindications. The differences that matter are pharmacokinetic — how the body absorbs, distributes, and clears the drug.
The headline difference: duration
This is the single most important distinction, and the reason the two medicines suit different people.
| Medicine | Active ingredient | Onset | Duration of effect |
|---|---|---|---|
| Cialis | Tadalafil | 30–60 minutes | Up to 36 hours |
| Viagra | Sildenafil | 30–60 minutes | 4–6 hours |
Viagra gives you a window of several hours. Cialis gives you a window of more than a day — which is why it is sometimes called the "weekend pill." A single Cialis tablet taken on Friday evening can still be effective on Sunday morning.
This is not marketing. It reflects tadalafil's much longer half-life (around 17.5 hours, compared with around 4 hours for sildenafil). The practical consequence is the biggest differentiator in everyday use:
- Viagra suits men who plan sexual activity in advance and want a short-acting, lower-cost medicine that clears the body quickly.
- Cialis suits men who want spontaneity — a wider window in which the medicine is active, without needing to time a tablet precisely.
A 2022 systematic review of patient preference studies (Kim et al.) found that, when men were given a choice between the two, a majority preferred tadalafil — and the leading reason cited was the longer duration and the freedom from timing tablets around sex.
Onset: a smaller difference than people assume
Both medicines typically start working within 30 to 60 minutes. Sildenafil may feel slightly faster for some men (sometimes within 25–30 minutes), but the difference is modest and varies between individuals. Neither is "instant."
One practical difference: food.
- Viagra (sildenafil) absorption is significantly slowed by a heavy or high-fat meal. Taking sildenafil with a large dinner can delay onset by an hour or more. For reliable timing, sildenafil is best taken on an empty stomach or with a light meal.
- Cialis (tadalafil) absorption is not meaningfully affected by food or alcohol (in moderation). You can take it with or without food, which removes a layer of planning.
If your pattern involves a meal before sex, Cialis is the more predictable option.
A difference Viagra cannot match: daily dosing
This is where Cialis pulls away in terms of flexibility. Cialis is the only PDE5 inhibitor licensed in Europe for once-daily use at a low dose.
| Cialis regimen | Dose | Who it suits |
|---|---|---|
| On-demand | 10 mg or 20 mg before activity | Men who have sex occasionally |
| Daily | 2.5 mg or 5 mg every day | Men who have sex more than twice a week, or who prefer not to plan |
Daily tadalafil maintains a steady low level of the medicine in the bloodstream at all times. That means no waiting for a tablet to take effect, no planning around a window, and the ability to be spontaneous any day. It also means you are taking a small dose continuously rather than a larger dose occasionally.
Viagra is licensed only for on-demand use. There is no approved daily regimen for sildenafil.
A use Cialis has that Viagra does not: BPH
Tadalafil is also EMA-approved for the signs and symptoms of benign prostatic hyperplasia (BPH) — the urinary symptoms of an enlarged prostate (weak stream, frequent urination, nocturia). The 5 mg daily dose is specifically approved for men who have both ED and BPH, treating both with one daily tablet.
Sildenafil is approved only for erectile dysfunction. If you have lower urinary tract symptoms alongside ED, Cialis is the only one of the two that can address both.
Side effects: mostly shared, with two differences
Because both drugs inhibit PDE5, their side-effect profiles overlap heavily. The common side effects of both include:
- Headache
- Flushing (facial warmth and redness)
- Indigestion / heartburn
- Nasal congestion
- Dizziness
- Back pain or muscle aches (more common with tadalafil)
- Visual disturbance (a blue tint to vision, more commonly reported with sildenafil)
Most side effects are mild and pass as the medicine clears the body.
Two differences are worth knowing:
Back pain and muscle aches are reported more often with tadalafil than with sildenafil. This reflects tadalafil's longer duration — the medicine (and its effects on smooth muscle) is present in the body for much longer. These effects typically resolve within 48 hours.
Duration of side effects. Because Cialis lasts up to 36 hours, any side effect you experience can also persist for longer. If a side effect is bothersome, sildenafil clears the system far more quickly.
Rare but serious effects — same warning for both
Both medicines carry the same rare-but-serious warnings:
- Priapism — a prolonged erection lasting more than 4 hours, unrelated to sexual stimulation. This is a medical emergency that can cause permanent damage and requires immediate hospital treatment.
- Sudden vision loss — rare reports of non-arteritic anterior ischaemic optic neuropathy (NAION). The evidence here is genuinely debated: a 2023 meta-analysis (Belladelli et al.) found no clear association between PDE5 inhibitor use and ocular events, while a separate 2022 pharmacovigilance study (Etminan et al., JAMA Ophthalmology) identified a signal of increased risk. Both studies are cited here because the question is not settled; anyone experiencing sudden vision loss should stop the medicine and seek urgent care.
- Sudden hearing loss — stop the medicine and contact a doctor immediately.
- Severe low blood pressure — the risk rises sharply if either medicine is combined with nitrate medicines (for chest pain). This combination is absolutely contraindicated and can be life-threatening.
What you absolutely cannot take with either
The following apply to both Cialis and Viagra:
- Nitrates (glyceryl trinitrate, isosorbide mononitrate/dinitrate, nitrate-containing recreational drugs such as "poppers") — combining these with a PDE5 inhibitor can cause a dangerous, potentially fatal drop in blood pressure. This is the single most important contraindication.
- Alpha-blockers (used for high blood pressure or prostate symptoms) — can be combined only with careful dose spacing and medical supervision, due to the risk of low blood pressure.
- Certain other medicines — including some HIV protease inhibitors (e.g. ritonavir) and antifungals (ketoconazole, itraconazole), which can raise PDE5 inhibitor levels in the blood.
Always give the reviewing doctor a complete list of everything you take — prescription, over-the-counter, and recreational. A 2026 pharmacovigilance study (Sridharan et al.) reinforced that clinically significant low blood pressure events with PDE5 inhibitors are most strongly associated with co-administration with nitrates and blood-pressure-lowering therapy.
Cost and availability
Both Cialis and Viagra are now off-patent in Europe, and generic tadalafil and sildenafil are widely available from licensed EU pharmacies at significantly lower prices than the original brands. Generic sildenafil is typically the lowest-cost option in the PDE5 class. Brand-name Cialis remains the more expensive option, particularly for daily use.
Pricing varies by country, pharmacy, dose, and pack size. On intermediary platforms, the consultation (doctor review) is usually priced separately from the medicine and delivery.
Which is right for you? A quick guide
There is no universally "better" option. According to a 2026 network meta-analysis of 83 randomised trials (Salonia et al., The Journal of Sexual Medicine), sildenafil 50 mg and 100 mg had the greatest odds of restoring satisfactory erectile function among the licensed PDE5 inhibitors, ahead of tadalafil 20 mg — so the raw-efficacy edge sits with sildenafil at full dose. The same analysis found tadalafil had the lowest odds of treatment-related adverse events, and its 36-hour window remains the main practical differentiator. Head-to-head differences are modest, and individual suitability is not a statistics question.
As a starting point for a conversation with a doctor:
Viagra (sildenafil) may suit you if:
- You want a short-acting medicine that clears the body quickly
- You plan sexual activity in advance
- Cost is a primary concern (generic sildenafil is the cheapest option)
- You want the medicine with the longest post-market safety record
Cialis (tadalafil) may suit you if:
- You value spontaneity and a longer window of effectiveness
- You have sexual activity more than twice a week (daily dosing becomes practical)
- You also have BPH symptoms
- You want a medicine that is not affected by food
- You prefer not to time tablets around sex
These are starting points, not decisions. Whether either medicine is appropriate for you at all — and at what dose — depends on your cardiovascular health, other medical conditions, and any other medicines you take. That judgement belongs to an independent, qualified doctor.
How to access either medicine in Europe
Both Cialis and Viagra are prescription-only medicines across the EU. They cannot be legally supplied without a prescription from a registered medical professional.
On an intermediary platform like Prescrivia, the process is:
- Complete a structured health assessment covering your medical history, current symptoms, and medications.
- An independent EU-registered doctor reviews your case. If a PDE5 inhibitor is clinically appropriate for you, they may issue a prescription and recommend a specific medicine and dose. If it is not appropriate — for example because of a contraindication — they will explain why.
- If a prescription is issued, it is sent to a licensed EU pharmacy partner, which dispenses and ships the medicine.
You can start from either medicine page — Cialis or Viagra — or browse all erectile dysfunction treatments.
A prescription is never guaranteed before that clinical assessment. Any service that promises a prescription before a doctor has reviewed your health is operating illegally and should be avoided.
The bottom line
Cialis and Viagra are both effective, well-studied, EMA-approved treatments for erectile dysfunction. They share a mechanism and most of their risks. The differences that matter in practice are:
- Duration — Cialis lasts up to 36 hours; Viagra lasts 4–6 hours.
- Dosing flexibility — Cialis offers a licensed daily option; Viagra does not.
- Food — Viagra is slowed by heavy meals; Cialis is not.
- Additional use — Cialis is also approved for BPH; Viagra is not.
- Cost — generic sildenafil is typically the cheapest option.
The right choice is personal, clinical, and depends on your overall health. The role of an intermediary platform is to connect you with an independent doctor who can make that judgement — not to sell you a particular medicine.
Sources
- European Medicines Agency (EMA). Cialis (tadalafil) — Summary of Product Characteristics. EMEA/H/C/000436.
- European Medicines Agency (EMA). Viagra (sildenafil) — Summary of Product Characteristics. EMEA/H/C/000202.
- Salonia A, et al. (2026). A comparative evaluation of on-demand phosphodiesterase-5 inhibitor efficacy in erectile dysfunction treatment: a systematic review and network meta-analysis of double-blind, placebo-controlled, randomized trials. The Journal of Sexual Medicine. PMID: 42296271.
- Kim HK, et al. (2022). Patient preference for tadalafil versus sildenafil in the treatment of erectile dysfunction: a systematic review. PMID: 35225813.
- Belladelli A, et al. (2023). Use of phosphodiesterase type 5 inhibitors and risk of ocular adverse events: a systematic review and meta-analysis. PMID: 37861186.
- Etminan M, et al. (2022). Risk of ocular adverse events associated with phosphodiesterase type 5 inhibitors. JAMA Ophthalmology. PMID: 35389459.
- Sridharan K, et al. (2026). Phosphodiesterase type 5 inhibitors and hypotension adverse events: a pharmacovigilance analysis. PMID: 42170200.