Sildenafil is the active ingredient in Viagra. Tadalafil is the active ingredient in Cialis. The NHS lists four medicines of this kind for erection problems: sildenafil (Viagra), tadalafil (Cialis), vardenafil (Levitra) and avanafil (Spedra). We supply all four after a consultation reviewed by a GPhC-registered pharmacist.
This guide explains how they differ. It does not rank them. Which one suits you depends on you, and the pharmacist decides whether a medicine and a dose are right for you.
What is the difference between sildenafil and tadalafil?
Both are PDE5 inhibitors that work the same way. So are vardenafil and avanafil. The main differences are how long before sex you take each one, how long its effect can last, and that tadalafil can also be taken once a day at a lower dose.
| Medicine | Strengths | Usual starting dose | How often | Most we can supply |
|---|---|---|---|---|
| Sildenafil (Viagra) | 25mg, 50mg, 100mg | 50mg | Never take more than one tablet in 24 hours. | Maximum 8 tablets per 2 weeks |
| Tadalafil, taken when needed (Cialis) | 10mg, 20mg | 10mg | Take one tablet no more than twice a week, and never more than once in 24 hours. | Maximum 8 tablets per 4 weeks |
| Tadalafil, daily (Cialis) | 2.5mg, 5mg | 5mg | Take one tablet a day, at about the same time each day. | 28 tablets on a first supply, up to 56 on later supplies |
| Vardenafil (Levitra) | 5mg, 10mg, 20mg | 10mg | Never take more than one tablet in 24 hours. | Maximum 8 tablets per 2 weeks |
| Avanafil (Spedra) | 50mg, 100mg, 200mg | 100mg | Never take more than one tablet in 24 hours. | Maximum 8 tablets per 2 weeks |
The pharmacist may start you on a lower dose, for example if you take an alpha-blocker or have a liver problem. There is more on this below.
Do they work on their own?
No. These tablets only work with sexual stimulation.
When you are sexually aroused, your body releases nitric oxide in the penis. This sets off a chemical signal that relaxes the blood vessels there, so blood can flow in and cause an erection. An enzyme called PDE5 breaks that signal down. All four tablets block PDE5, so the signal lasts longer. That is why they are called PDE5 inhibitors. Without arousal there is no signal for them to act on.
When do I take each one, and how long does it last?
- Sildenafil: take it about 1 hour before sex (anywhere from 30 minutes to 2 hours before). It takes about an hour to work.
- Tadalafil: take it at least 30 minutes before sex. It takes about 30 to 45 minutes to work, and its effect can last more than 24 hours.
- Vardenafil: take it 25 to 60 minutes before sex. It takes about 30 minutes to work.
- Avanafil: take the 100mg or 200mg tablet 15 to 30 minutes before sex, or the 50mg tablet about 30 minutes before. The 100mg and 200mg tablets can work in about 15 minutes. It lasts about 6 hours.
Each one is taken only when you need it, apart from daily tadalafil (below). Try a tablet 4 to 8 times before deciding it does not work, then tell us.
Does food or alcohol affect them?
A heavy or high-fat meal can delay how quickly sildenafil, vardenafil and avanafil work. Tadalafil is not affected by food.
Drinking less alcohol can help your erections. With tadalafil or avanafil, alcohol can also make low blood pressure more likely, which can make you feel dizzy or light-headed.
Grapefruit juice can raise the amount of these medicines in your blood:
- Sildenafil: avoid grapefruit and grapefruit juice.
- Tadalafil: avoid grapefruit juice.
- Vardenafil: avoid grapefruit and grapefruit juice.
- Avanafil: avoid grapefruit juice in the 24 hours before you take it.
What is daily tadalafil, and who is it for?
Tadalafil can also be taken once a day at a lower dose, 2.5mg or 5mg. It is for men who expect to have sex at least twice a week.
Take one tablet a day, at about the same time each day. You take it whether or not you plan to have sex that day. The available data does not suggest that taking it every day works better than taking tadalafil when needed.
- How much we supply: 28 tablets on a first supply, up to 56 on later supplies.
- Not offered if: you have any liver or kidney disease, or you take doxazosin.
- Blood pressure medicines: if you take them, tadalafil can lower your blood pressure further. If you feel dizzy or sick, see your GP to review your blood pressure medicine.
- GP notification. Daily tadalafil should be added to your regular medication record. We will contact your GP with your consent, or you can tell them yourself. Will you tell my GP?
More on the daily tadalafil page.
How often can I take each one?
- Sildenafil, vardenafil and avanafil: Never take more than one tablet in 24 hours.
- Tadalafil, taken when needed: Take one tablet no more than twice a week, and never more than once in 24 hours.
- Daily tadalafil: Take one tablet a day, at about the same time each day.
There is also a limit on how much we can supply: 8 tablets every 2 weeks for sildenafil, vardenafil and avanafil, and 8 tablets every 4 weeks for tadalafil taken when needed. If you expect to need treatment more than twice a week, the consultation shows you daily tadalafil first, and tadalafil taken when needed is not offered.
Which one is right for me?
No one tablet suits everyone. These are the things that decide it, and the pharmacist checks each of them in your consultation.
- How often you have sex. Daily tadalafil is for about twice a week or more. Tadalafil taken when needed is not for more than twice a week.
- How far ahead you want to plan. Each tablet is taken a different time before sex, as listed above, and tadalafil's effect can last more than 24 hours.
- Other medicines you take. Alpha-blockers, often used for prostate symptoms or blood pressure, need care with all four. We do not offer tadalafil taken when needed with any alpha-blocker, daily tadalafil with doxazosin, or avanafil with tamsulosin or doxazosin. With an alpha-blocker, your dose needs to have stayed the same recently, without dizziness or fainting, and you start on the lowest dose. Erythromycin, aprepitant, diltiazem, fluconazole and verapamil can mean a lower dose. With avanafil: Take no more than one avanafil tablet in 48 hours.
- Your health. A liver problem means a lower starting dose of sildenafil, vardenafil or avanafil, and no more than 10mg of tadalafil taken when needed. Daily tadalafil is not offered with any liver or kidney problem. Avanafil needs a blood pressure reading below 170/100. You can choose another treatment, or have your blood pressure checked and come back. Avanafil is also not offered after a serious heart rhythm problem in the last 6 months.
- What you have tried before. If a medicine has not worked after 4 to 8 tries at the highest dose that suits you, your pharmacist may suggest trying a different one.
The pharmacist decides your starting dose. A first order is usually for the starting dose, or a lower one if your answers call for it. If you switch to a different medicine, you start it at its starting dose, even if you took a higher dose of the one before.
Losing weight, stopping smoking, drinking less alcohol and exercising can all help. If you cycle more than 3 hours a week, try a break from cycling.
Not sure which suits you? Answer a few questions about your health and the medicines you take. A GPhC-registered pharmacist reviews every consultation, and if they cannot approve your order, we refund you in full automatically.
Start your consultationAre the side effects different?
The common side effects listed for each medicine are:
- Sildenafil: Very common / common side effects include headache, dizziness, flushing, nasal congestion, dyspepsia (indigestion), nausea and vision disturbances.
- Tadalafil, taken when needed: Common side effects include headache, flushing, nasal congestion, dyspepsia (indigestion), back pain, myalgia (muscle aches) and pain in the arms and legs.
- Tadalafil, daily: Common side effects include flushing, nasal congestion, dyspepsia (indigestion), headache, back pain, myalgia (muscle aches) and pain in the arms and legs.
- Vardenafil: Very common / common side effects include headache, flushing, nasal congestion, dyspepsia, and dizziness.
- Avanafil: Common side effects include headache, flushing and nasal congestion.
Less common side effects are listed in the leaflet in your pack. Please read it before your first dose.
Each list comes from that medicine's own product information, so the lists cannot be compared to show that one medicine causes fewer side effects than another. These tablets can affect your ability to drive or use machines. Tell us or your GP about any side effect. You can also report it to the MHRA Yellow Card scheme.
Who should not take any of them?
None of the four is suitable if any of these apply to you:
- Nitrates in any form, including nicorandil or amyl nitrite (poppers)
- Riociguat (Adempas), vericiguat (Verquvo) or another guanylate cyclase stimulator
- Stroke or heart attack in the last 6 months
- Unstable angina, or angina during intercourse
- A heart condition for which a doctor has told you to avoid sex or strenuous activity
- Very low blood pressure, below 90/50
Nitrates include GTN spray, isosorbide mononitrate and isosorbide dinitrate, often used for chest pain. Taken with any of these tablets, nitrates and the medicines above can lower your blood pressure too far.
If you ever need emergency treatment for chest pain, tell the doctor or paramedic which of these tablets you take and when you last took it. Tadalafil's product information says that at least 48 hours should pass after the last dose of tadalafil before a nitrate is considered, even in an emergency.
Do not take two erectile dysfunction medicines together. Do not use unlicensed herbal remedies for erections, and do not stop any prescribed medicine unless your doctor tells you to.
These are not the only reasons. The consultation also asks about your other medicines, your eyes, your liver and kidneys, and stops if a tablet would not be safe for you.
Why does my pack say sildenafil or tadalafil instead of Viagra or Cialis?
The sildenafil, tadalafil and vardenafil we supply are generic versions. Each contains the same active ingredient as the brand, at the same strength, and is licensed in the UK. The pack shows the medicine's name and the name of the company that makes it, instead of the brand name.
Tablets made by different companies can look different, even when the medicine and the strength are the same.
Already a Solira patient? If a new pack looks different and you are not sure it is right, message your pharmacist through your account before you take it.
Your order comes in plain packaging, with no medicine names on it. Is the packaging discreet?
Can I get Viagra or Cialis without a prescription?
Two branded tablets can be sold by a pharmacy without a prescription: Viagra Connect (sildenafil 50mg) and Cialis Together (tadalafil 10mg). The MHRA made Viagra Connect a pharmacy medicine in November 2017, and Cialis Together in March 2023. We offer both after a pharmacist consultation, for men aged 18 to 64. See Viagra Connect and Cialis Together, or all our erectile dysfunction treatments.