07 September, 2020 | Jabbar Ali - MPharm
Viagra or Cialis, which is the better erectile dysfunction pill online? Unfortunately, there is no simple answer to this question. Knowing the differences between these two erectile dysfunction medications can help you make a better choice.
Both work. Both are licensed in the UK, both are backed by years of clinical evidence, and both help around four in five men who use them. The real question is not which medicine is stronger, but which one fits the way you actually live. Cialis stays active far longer and suits men who do not want to plan around a tablet. Viagra is shorter acting, cheaper and better understood by most men starting treatment.
This guide compares them properly. It looks at how fast each one works, how long it lasts, the cost difference between branded and generic, and more.
| Viagra | Cialis | |
|---|---|---|
| Active ingredient | Sildenafil | Tadalafil |
| Drug class | PDE5 inhibitor | PDE5 inhibitor |
| Time to take effect | Around 30 to 60 minutes | Around 30 to 60 minutes |
| How long it lasts | Four to six hours | Up to 36 hours |
| Effect of food | Heavy or fatty meals can delay and reduce its effect. Best on an emptier stomach. | Not affected by food |
| Effect of alcohol | Excess alcohol can reduce effectiveness | Alcohol may interfere with effectiveness |
| Dosing options | On demand only, taken before sexual activity | On demand, or a lower strength taken every day |
| Generic version | Sildenafil | Tadalafil |
| Available without a prescription | Yes, as Viagra Connect from a pharmacy | Yes, as Cialis Together from a pharmacy |
| Often suits | Men who want treatment for a specific occasion, and those wanting the lowest cost per tablet | Men who want spontaneity, or sex more than once or twice a week |
The table covers the practical differences. The sections below explain what they mean in real life.
Along with Levitra and Spedra, Viagra and Cialis are the most popular erectile dysfunction pills online. All these medications belong to a class of drugs called PDE5 inhibitors and work in a similar manner, by improving blood flow to the penis. In the presence of sexual arousal, these medications help men obtain erections required for penetrative sex. Viagra and Cialis are branded medications and can also be purchased in their generic form, sildenafil (generic form of Viagra) and tadalafil (generic form of Cialis).
That shared mechanism is worth understanding, because it explains a lot of what follows. Neither medicine creates desire or produces an erection on its own. Both work by relaxing the blood vessels supplying the penis so that, when you are aroused, more blood can flow in and stay there. If nothing happens the first time you try one, that is usually a matter of timing, expectation or dose rather than the medicine failing. You can read more in our complete guide to erectile dysfunction.
The main difference between Viagra and Cialis relates to how long they remain in the system and effective.
The effects of Viagra can last for four to six hours whereas the effects of Cialis can last for up to thirty six hours.
That 36 hour window is why Cialis is often nicknamed the weekend pill. It does not mean 36 hours of continuous erection, which is not how any of these medicines work. It means that for up to a day and a half after taking it, you are able to get an erection when you are aroused, without thinking about the tablet at all. For a lot of men that difference matters more than anything else on this page.
Viagra needs to be taken 30 to 60 minutes before planned sexual activity, preferably on an empty stomach since heavy meals can reduce this medication’s effectiveness.
Cialis is taken in a similar timeframe, but because it stays active so much longer, precise timing matters far less. Many men take it earlier in the day, or the evening before, and simply stop thinking about it.
Cialis is not affected by food intake but alcohol may interfere with its effectiveness. Some people prefer Cialis because it involves less planning.
Viagra is the more sensitive of the two here. A large, fatty meal can noticeably delay how quickly it works and blunt the effect, which is one of the most common reasons men think their first dose has not worked. With either medicine, heavy drinking is unhelpful, since alcohol makes erections harder to achieve regardless of what you have taken.
Both medicines are long past patent, so generic versions are available: sildenafil for Viagra and tadalafil for Cialis. A generic contains the same active ingredient at the same strength and is held to the same regulatory standards as the branded product. The only meaningful difference is the price, and it is substantial.
Sildenafil is generally the cheapest option per tablet of any ED treatment, which is part of why it remains the most commonly prescribed. Tadalafil costs a little more per tablet but covers a much longer window, so for men having sex more than once in a weekend it can work out better value. If cost is your deciding factor, generic sildenafil is the place to start.
Different erectile dysfunction medications affect people in different ways. The correct choice depends on several factors including existing medical conditions and medications a person might be using. For example, Cialis is not recommended for men who are on alpha blockers. Men who are using alpha blockers can consider Viagra as an alternative, however they must accommodate a six hour time gap between taking the alpha blocker and Viagra.
It is worth adding that the alpha blocker interaction applies to both medicines to differing degrees, and which one is suitable depends on the specific alpha blocker you take and the dose. This is exactly the sort of detail a prescriber checks during your consultation, which is why the medical questionnaire matters.
Neither Viagra nor Cialis, in branded or generic form, should ever be taken alongside nitrate medication such as glyceryl trinitrate (GTN spray or tablets), isosorbide mononitrate or nicorandil, which are commonly prescribed for angina. Combining a PDE5 inhibitor with a nitrate can cause a sudden and dangerous drop in blood pressure. This applies equally to both medicines and is not negotiable.
Other situations that need a prescriber’s judgement include a recent heart attack or stroke, very low or poorly controlled blood pressure, severe liver or kidney problems, and certain eye conditions. Because ED can itself be an early sign of cardiovascular problems, it is also worth reading our guide to erectile dysfunction and cardiovascular health. Declare everything you take, including anything bought over the counter, when you complete your consultation.
Viagra and Cialis have similar side effects such as headache, stuffy nose, flushed facial appearance, stomach upset, nausea, vomiting and blurred vision.
These are usually mild and short lived, and they tend to ease as your body gets used to the medicine. There is one difference worth knowing: because tadalafil stays in your system far longer, any side effects you do get can linger for longer too, and back or muscle ache is reported slightly more often with tadalafil than with sildenafil. Sildenafil is marginally more associated with visual disturbances such as a blue tinge to vision.
Seek medical attention if you experience chest pain during sex, a sudden loss of vision or hearing, or an erection lasting more than four hours, which is a medical emergency. Full frequency data for each medicine is set out in its patient information leaflet on the EMC website.
While requesting any erectile dysfunction pill online from an authorised UK internet pharmacy, answer the medical questionnaire honestly so that a qualified doctor can evaluate your suitability for the medication and provide a free e-prescription in case you do not have one. Both medications are available in different strengths and it is best to request the recommended starting dose.
If the starting dose does not give you the result you want, that does not mean the medicine has failed. Prescribers usually suggest trying it a few times before drawing conclusions, since timing, food, alcohol and nerves all affect the first attempt. From there, the dose can be adjusted or you can switch to the other medicine. Many men try one, then the other, before settling.
Partly. Lower strength versions of both are now available from pharmacies without a prescription, after a consultation with the pharmacist: Viagra Connect (sildenafil) and Cialis Together (tadalafil).
These are a reasonable starting point, but they come in one strength only. If that strength is not right for you, or you want the daily dosing option or a higher dose, you will need a prescription. Our guide to Viagra Connect explains the differences in more detail. Wherever you buy, buy from a registered UK pharmacy. Sites selling prescription ED medication without any consultation are operating illegally and the product may not be what it claims to be.
Viagra and Cialis are both effective, both well tolerated by most men, and both available as much cheaper generics. The right one for you comes down to how often you want to use it, how much you value spontaneity, what else you take and what you want to spend.
“The question our pharmacists hear most is which one is stronger, and the honest answer is neither. What matters is how often you want to use it, what else you take and your heart health, which is why every consultation is reviewed before we prescribe. If the first choice doesn't suit you, we can adjust the dose or switch you to the other.”
Omar El-Gohary, Superintendent Pharmacist and CEO, iQ Doctor (GPhC Reg. No. 2059792)
iQ Doctor is a registered UK pharmacy that specialises in medical remedies for erectile dysfunction, weight loss, hair loss support and much more. Complete a short online consultation, have it reviewed by a UK registered prescriber, and receive your treatment discreetly. If you are unsure which option suits you, get in touch with IQ Doctor's clinical team.
No. Neither is stronger, they simply behave differently. Both work for a similar proportion of men. Cialis stays active much longer, which is often mistaken for being more powerful, but the effect itself is comparable.
Up to 36 hours. That means you can get an erection when aroused at any point in that window, not that the effect is continuous. Viagra lasts around four to six hours by comparison.
No. Never take two PDE5 inhibitors at the same time. Doing so increases the risk of side effects, particularly a dangerous drop in blood pressure, without improving the result. If one is not working for you, speak to a prescriber about switching rather than combining.
Yes. Generic sildenafil contains the same active ingredient at the same strength and meets the same UK regulatory standards. The difference is price, not effectiveness. The same applies to tadalafil and Cialis.
Neither is unaffected, but Cialis is generally the more forgiving choice around a meal and a drink, since food does not interfere with it and its long duration means a delayed effect matters less. Heavy drinking makes erections harder regardless of which medicine you take.
Yes, and many men do. Do not switch mid-dose or take both close together. Speak to your prescriber, who can advise on timing and the right starting dose for the alternative.
For most strengths, yes. Lower strength Viagra Connect and Cialis Together are available from pharmacies without a prescription following a consultation. Anything beyond that requires a prescriber to review your medical history first.
This page has been written by a registered UK pharmacist and reviewed by our clinical team to ensure it is accurate, clear and reflects current clinical guidance.
Last medically reviewed: 07 September, 2020
Last updated: 13 October, 2026