Cialis vs Viagra: Which is Better for ED?

A man holding a Viagra tablet and a Cialis tablet
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Both sildenafil and tadalafil have a high success rate and there isn’t one that is “better” than the other. They can vary in effectiveness depending on the individual. Sildenafil and tadalafil are both effective and proven treatments for erectile dysfunction. Sildenafil is the active ingredient in Viagra, and is available as a generic (non-branded) version. Tadalafil is the active ingredient in Cialis, also available as a generic version. Whilst they both belong to the same class of drugs, known as PDE5 inhibitors, they differ slightly in certain areas such as their duration of action and side-effects. This article looks at the difference between Cialis and Viagra. 


Quick overview


Sildenafil (Viagra)

Tadalafil (Cialis) 36-hour

Tadalafil (Cialis) Daily


Prices from £5.89

Prices from £8.99

Prices start from £19.45


25mg, 50mg, 100mg

10mg, 20mg

2.5mg, 5mg


To be taken 1 hour before sexual activity

To be taken 30 minutes before sexual activity

To be taken everyday

Duration of action

Lasts for 4-6 hours

Lasts for up to 36 hours

Continuous effect whenever there is sexual stimulation

Time taken to work

Works within 30-60 minutes

Work within 20-30 minutes

Works spontaneously upon sexual stimulation

How it is taken?

Can be taken with or without food, but most effective when taken on an empty stomach

Can be taken before or after food, but more effective when taken on an empty stomach

Can be taken with or without food

Side-effects (common)*

Headache, facial flushing, nasal congestion

Headache, facial flushing, nasal congestion


Prescription required?

Yes (except for 50mg which is available over the counter as Viagra Connect and Eropid)



Unique selling points

  • Cost-effective
  • Available as multiple strengths
  • Can be bought over the counter
  • Works quickly
  • Has a long duration of action
  • Can be used continuously for spontaneous sexual activity
  • Low side-effect profile

*For a full list of side-effects, please consult product literature


What is sildenafil?

Sildenafil is a drug that is used to treat erectile dysfunction. It works by relaxing the smooth muscle in the penis, when there is sexual stimulation. This allows blood to enter the penis easily, causing an erection. It can help to stimulate an erection that is harder, and lasts longer. Sildenafil was first introduced to the market by Pfizer in 1998, as Viagra. They had a license, also known as a patent, to be the only supplier of sildenafil. When this patent expired in 2013, it opened the door to other pharmaceutical companies, allowing them to manufacture sildenafil as a generic (non-branded) version. Pfizer had invested a huge sum of money in developing Viagra, as well as in clinical trials and marketing. This is the reason that Viagra is so expensive. The other companies that manufacture sildenafil already have the ingredients, and do not need to pay for clinical trials or marketing, as this has already been done by Pfizer. This is the reason that the generic version of sildenafil is available at a much lower cost. The active ingredient is exactly the same and they both are equally as effective as each other. 


What is tadalafil?

Tadalafil is also a drug that is used to treat erectile dysfunction. Similar to sildenafil, tadalafil works by allowing smooth muscles to relax in the penis, widening blood vessels. This allows blood to enter the penis when there is sexual stimulation, resulting in an erection. Tadalafil was first introduced to the market in 2003 as Cialis, by the pharmaceutical company Ely Lilly. The patent for Cialis expired in 2017, allowing other pharmaceutical companies to manufacture a non-branded (generic) version at a cheaper price. Both generic tadalafil and Cialis contain the same active ingredient, and there is no difference in effectiveness between the two.


What lasts longer, sildenafil or tadalafil?

Tadalafil lasts longer than sildenafil. Sildenafil has a duration of action for up to 4 hours, whilst tadalafil can last for up to 36 hours. This does not mean you will have a constant erection for the time periods each drug is active for. It means that you will achieve an erection upon sexual stimulation, for the time period that the drug is active for. Tadalafil 2.5mg and 5mg (tadalafil daily) can be taken every day, and is best suited for those that have more than 2 sexual encounters per week.


What works quicker, tadalafil or sildenafil?

Tadalafil works quicker than sildenafil by around 10-20 minutes on average. Sildenafil works around 30-60 minutes after it has been taken, whereas tadalafil works around 20-30 minutes after it has been taken. This can depend on the individual and how they respond to each treatment. Both sildenafil and tadalafil work best on an empty stomach. Taking tadalafil or sildenafil after a meal is likely to increase the length of time it takes to work.


What has the least side-effects, sildenafil or tadalafil?

Both tadalafil and sildenafil have a similar side-effect profile, but the side-effects of tadalafil may last longer, due to its larger window of action. However, sildenafil has a longer list of common side-effects that don’t appear to be as common in tadalafil. A common side-effect of both, include headache. You may also encounter facial flushing, which is when your face experiences a rapid sensation of warmth. Nasal congestion is another common side-effect of tadalafil and sildenafil.


Which one has a higher success rate?

Both tadalafil and sildenafil have proven to have similar success rates in clinical trials, with both proving that they are effective in over 80% of those that use either drug. A study conducted by a hospital in China, showed that tadalafil was preferred by men, and that their partners also preferred the effect that that tadalafil had over sildenafil. Another clinical trial carried out in Italy, showed that 73% of men preferred tadalafil over sildenafil.


Do you need a prescription for tadalafil or sildenafil?

Both tadalafil and sildenafil require a prescription, with the exception of Viagra Connect, which can be bought over the counter. To obtain sildenafil or tadalafil, you should visit your doctor, who will asses you before prescribing either drug. Erectile dysfunction treatment is not available on the NHS, unless you have a certain medical condition, and you will need to pay the private cost of the treatment. There is no set fee, and pharmacies are able to charge their own price for these treatments. You are also able to buy ED treatment online, after completing an online questionnaire. You are able to purchase Viagra Connect from a local pharmacy, after having a consultation with the pharmacist. Alternatively, you are also able to buy Viagra Connect online, after answering questions relating to your health.


How do I know which one to use?

The only way to know whether you should use tadalafil or sildenafil, is to try both treatments. You should speak to a pharmacist or doctor about which one to try. This can depend on various factors surrounding your sexual activity and preferences. If you have tried one tablet, you should try it a few times to allow your body to get used to it. If you aren’t experiencing the desired effects, you should try a higher strength the next time. If you have reached the maximum strength, and you have tried it a few times without the desired effect, you should speak to your doctor or pharmacist about trying an alternative.


Is Cialis 20mg equal to Viagra 100mg?

These strengths are both the highest doses available. Both are more likely to illicit a response, where the lower doses have not worked. However, they both need to be taken at differently, and differ in their duration of action.


Can you take tadalafil and sildenafil together?

You cannot take tadalafil and sildenafil together, or on the same day. Taking more than one ED treatment at the same time, or on the same day can cause unwanted and potentially harmful side effects. This can include, dizziness, nausea, indigestion and a painful erection lasting longer than 4 hours. You can however, use both treatments on different days. 


So, sildenafil vs. tadalafil – which one is better?

On paper, tadalafil is better than sildenafil as it offers various advantages, mainly its longer duration of action. It also works faster than sildenafil, with milder side-effects. Whilst both treatments are more effective on an empty stomach, tadalafil is not affected by food to the same extent as sildenafil is. However, the truth is that individuals vary in their response to different treatment. Some men prefer sildenafil despite having tried tadalafil, and vice versa. You can see how our customers rate each treatment by looking at our sildenafil reviews and tadalafil reviews pages. 

Whilst all of our content is written and reviewed by healthcare professionals, it is not intended to be substituted for or used as medical advice. If you have any questions or concerns about your health, please speak to your doctor.