What is the difference between sildenafil and tadalafil?
The difference is duration: sildenafil works for 4 to 6 hours and tadalafil for up to 36 hours, while the effect on the erection itself is the same.
Both substances inhibit the enzyme PDE5, which would otherwise break down the signal substance that makes the blood vessels in the penis widen. With the enzyme slowed down, your own erection comes more easily and lasts longer when you are aroused. The medicine does not cause an erection by itself. It removes a brake; it does not press the accelerator.
Because the mechanism is the same, so is the effect. What separates them is how long the substance stays in the body. Sildenafil gives a window of a few hours, tadalafil a window of up to a day and a half. Window here means the period in which an erection comes more easily when you are stimulated, not that you have an erection all the time.
| Sildenafil (Viagra) | Tadalafil (Cialis) | |
|---|---|---|
| Works after | 30 to 60 minutes | 30 to 60 minutes |
| Duration | 4 to 6 hours | Up to 36 hours |
| Typical dose | 50 mg as needed (25 to 100 mg) | 10 to 20 mg as needed, or 5 mg daily |
| Food | A heavy meal delays the effect | Less affected by food |
| Common side effects | Headache, flushing, blocked nose, visual disturbances | Headache, back pain, muscle pain |
| Generic, per tablet | From DKK 2.86 (50 mg) | From DKK 2.90 (20 mg) |
Dosing and side effects according to the summaries of product characteristics. The doctor chooses type and dose after an individual assessment.
Does food affect sildenafil and tadalafil differently?
Yes, a heavy, fatty meal can delay the effect of sildenafil, while tadalafil is less affected by food.
Sildenafil works fastest on an empty stomach. If you eat a large, fatty dinner just before, it can take longer before the tablet works, and many then wrongly think the medicine does not work. Take it about an hour before, preferably before or long after a heavy meal.
Tadalafil can be taken regardless of meals and time, because it works over a long window. That is one of the reasons many find it more spontaneous.
Alcohol applies to both: a single glass is usually not a problem, but larger amounts weaken the erection by themselves and increase the risk of dizziness and a drop in blood pressure together with the medicine.
Who is sildenafil for, and who is tadalafil for?
Sildenafil suits planned occasions, while tadalafil suits you if you want a longer window and less planning.
- Sildenafil: you have sex at planned times, want precise control and prefer a shorter window. It is the type most men start on.
- Tadalafil as needed: you want to take the tablet on a Friday and have an effect over the weekend without watching the clock.
- Tadalafil 5 mg daily: you have sex often, or you do not want to plan at all. You take a small tablet every day and have a constant effect.
- Side effects also guide the choice: back pain on tadalafil or a blocked nose on sildenafil can be a reason to switch.
There is no single right answer for everyone. The doctor asks how often you have sex, what your occasions typically look like, your health and your other medication, and recommends the type that fits your everyday life.
How much do sildenafil and tadalafil cost in Denmark?
Generic sildenafil costs from DKK 2.86 per tablet and generic tadalafil from DKK 2.90 per tablet, while the originals Viagra and Cialis 20 mg cost over DKK 100 per tablet.
| Medicine | Pack | Pharmacy price |
|---|---|---|
| Sildenafil (generic) | 12 tablets of 50 mg | From DKK 34.30 (DKK 2.86 per tablet) |
| Sildenafil (generic) | 12 tablets of 100 mg | From DKK 47.70 (DKK 3.98 per tablet) |
| Viagra (original) | 12 tablets of 50 mg | DKK 1,292.85 |
| Viagra (original) | 4 tablets of 100 mg | DKK 529.45 |
| Tadalafil (generic) | 12 tablets of 20 mg | From DKK 34.80 (DKK 2.90 per tablet) |
| Tadalafil (generic) | 28 tablets of 5 mg, daily use | From DKK 43.85 |
| Cialis (original) | 4 tablets of 20 mg | DKK 419.90 |
| Cialis (original) | 28 tablets of 5 mg, daily use | DKK 690.10 |
Official pharmacy price including the prescription fee, the same at all Danish pharmacies, with no subsidy. See pharmacy prices today.
Generic medicine contains the same active substance in the same strength as the original, is approved under the same requirements and works the same way. The pharmacy offers the cheapest pack as a starting point. On top comes the doctor-led programme: at Recepta DKK 0 for the first 4 weeks, then DKK 104 per 4 weeks with a 1-year membership (DKK 1,349 paid yearly) or DKK 149 with no binding.
What is tadalafil 5 mg daily?
It is a small dose of tadalafil taken every day, so the effect is constant and you do not have to plan.
The daily dose is typically 5 mg, sometimes 2.5 mg. It suits men who have sex often, or who find it stressful to time a tablet. Generic tadalafil 5 mg costs from DKK 43.85 for 28 tablets, which is one pack per 4 weeks.
Who should not take sildenafil or tadalafil?
You must never take either if you use nitrate medicine such as nitroglycerin, because the combination can cause a life-threatening drop in blood pressure.
That includes nitroglycerin spray. You also cannot use the medicine with unstable heart disease, after a heart attack or stroke within the last 6 months, with very low blood pressure, with severe liver or kidney disease or with rare eye diseases that damage the optic nerve. Some blood pressure medicines of the alpha-blocker type require the doctor to plan the doses with a gap. An erection lasting more than 4 hours is an emergency, and you must go to A&E the same day.
Can you switch from sildenafil to tadalafil?
Yes, if the first type does not work well enough or fits your everyday life poorly, the doctor can adjust the dose or switch to the other.
Between 50 and 80% notice a clear effect of erectile dysfunction medicine. If the first type does not work, it is rarely because the treatment is wrong. Often the dose needs to go up, the timing needs adjusting, or another substance should be tried. Try a treatment a few times before concluding that it does not work.
Frequently asked questions
Is tadalafil stronger than sildenafil?
Which works faster, sildenafil or tadalafil?
Can I take sildenafil and tadalafil on the same day?
Which is cheaper in Denmark, sildenafil or tadalafil?
Is generic tadalafil the same as Cialis?
Does tadalafil cause more back pain than sildenafil?
Can I get sildenafil or tadalafil online in Denmark?
Sources
- European Medicines Agency (EMA): Summaries of product characteristics for Viagra (sildenafil) and Cialis (tadalafil). Dosing, contraindications (nitrates) and side effects.
- pro.medicin.dk: Sildenafil and tadalafil. Action, duration, dose, interactions and side effects.
- Goldstein I, Lue TF, Padma-Nathan H, et al. Oral sildenafil in the treatment of erectile dysfunction. New England Journal of Medicine. 1998;338(20):1397-1404.
- European Association of Urology (EAU): Guidelines on sexual and reproductive health, erectile dysfunction (2025).
- Recepta: pharmacy prices today, price period 28 September to 11 October 2026.
This page is health information and does not replace a medical assessment. Recepta does not sell medicine; prescription medicine is only dispensed after an individual assessment by a doctor and is bought at the pharmacy.