Sildenafil (the medicine in Viagra) and tadalafil (the medicine in Cialis) work in the same way, and for most men they work about as well as each other. The real differences are how long they last and how food affects them. Sildenafil lasts around 4 hours and works best on an empty stomach. Tadalafil lasts up to 36 hours, isn't affected much by food, and can also be taken as a low dose every day. Generic versions of both contain the same medicine as the brands and usually cost less.
"Which one is right for me?" is one of the questions we're asked most often. This guide sets out the differences so you can go into your erectile dysfunction treatment consultation knowing what to ask. Your prescriber will then decide what's suitable for you, based on your health and any other medicines you take.
Sildenafil and tadalafil at a glance
| Sildenafil (Viagra) | Tadalafil (Cialis) | |
|---|---|---|
| When to take it | About 1 hour before sex | At least 30 minutes before sex, or a low dose once a day |
| How long it lasts | Around 4 hours | Up to 36 hours |
| Food | A heavy or fatty meal can slow it down | Not affected much by food |
| Daily option | No | Yes (2.5mg or 5mg once a day) |
| Common side effects | Headache, flushing, indigestion, blocked nose, dizziness, changes in vision | Headache, flushing, indigestion, blocked nose, back pain, muscle aches |
| Generic available | Yes | Yes |
How sildenafil and tadalafil work
Sildenafil and tadalafil both belong to a group of medicines called PDE5 inhibitors. They relax the smooth muscle in the blood vessels that supply the penis, so more blood can flow in when you're aroused. That's what makes it easier to get and keep an erection.
Neither medicine causes an erection on its own. You still need to be sexually aroused for them to work. And because they act in the same way, you should never take them together, or take more than one dose of either in 24 hours.
If you'd like to understand why erection problems happen in the first place, our guide to the causes of erectile dysfunction covers the physical and psychological reasons.
Which is stronger?
Neither is stronger in any useful sense. At the right dose, both help most men get an erection firm enough for sex. Some men find one suits them better than the other, either because it works better for them or because they get fewer side effects with it.
The choice usually comes down to timing. Tadalafil's longer window means you don't have to plan sex around a tablet, which many men and their partners prefer. Sildenafil's shorter action suits men who have sex less often and would rather the medicine was out of their system sooner.
How soon they work and how to take them
Both usually start working within 30 to 60 minutes. Sildenafil is taken about an hour before sex and lasts around 4 hours; a heavy meal can slow it down, so it works best on an empty stomach or after a light meal. Tadalafil is taken at least 30 minutes before, isn't affected much by food, and lasts up to 36 hours.
It's common for the first dose not to work as well as you'd hoped, often because of nerves. It's worth trying the medicine up to 8 times, at a suitable dose, before deciding it doesn't work for you. If it still isn't helping, speak to your prescriber about a different dose or a different medicine.
Alcohol is best kept to a small amount. Drinking a lot makes erections harder to get, whatever medicine you take, and can make side effects such as dizziness worse.
Daily tadalafil
Tadalafil also comes as a low dose (2.5mg or 5mg) taken once a day, at about the same time each day. This keeps a steady level of the medicine in your body, so you don't need to plan around a tablet at all. It tends to suit men who expect to have sex at least twice a week.
Daily treatment isn't for everyone. It means taking a tablet every day whether you have sex or not, so it's worth discussing with your prescriber. You can read more on our daily tadalafil (Cialis Daily) page.
Are they safe?
For most men, both medicines are safe when prescribed after a proper check of your health. Side effects are usually mild and short-lived. Because tadalafil lasts longer, any side effects can last longer too.
There are some important exceptions:
- Don't take either if you use nitrate medicines (such as GTN spray or isosorbide) or "poppers", as the combination can cause a dangerous drop in blood pressure.
- They may not be suitable if you have heart problems, very low blood pressure, or have been told to avoid sexual activity.
- Tell your prescriber about all other medicines you take, including alpha-blockers for blood pressure or prostate problems.
- Take no more than one dose in 24 hours.
Get urgent medical help if you have an erection lasting more than 4 hours, chest pain, or sudden loss of vision or hearing.
Erection problems can sometimes be an early sign of heart disease, diabetes or high blood pressure. If they're new for you, it's worth seeing your GP for a check-up as well.
Brand or generic: does it matter?
Generic sildenafil and tadalafil contain the same medicine as Viagra and Cialis and usually cost much less. They must meet the same standards for quality and how well they work. The differences are the name, the look of the tablet and the price. Our guide to generic and brand-name medicines explains why this is.
Some men still prefer a brand they recognise, and that's a personal choice. Either way, the medicine you're prescribed depends on what's suitable for you.
Other options
Sildenafil and tadalafil aren't the only choices. Vardenafil works in a similar way to sildenafil and lasts for a similar time. Avanafil (Spedra) can start working within 15 to 30 minutes, which some men find useful. If one medicine hasn't suited you, another may.
There's also Viagra Connect, a 50mg sildenafil tablet that a pharmacist can supply without a prescription after checking it's suitable for you.
If you're wondering whether these medicines help with lasting longer, we cover that in does Viagra make you last longer?
Sildenafil vs tadalafil FAQs
Which lasts longer, Cialis or Viagra?
Tadalafil (Cialis) lasts much longer, up to 36 hours. Sildenafil (Viagra) lasts around 4 hours. Neither gives you a constant erection; you still need to be aroused.
Can I take tadalafil every day?
Yes, if it's prescribed that way. Daily tadalafil is a low dose (2.5mg or 5mg) taken once a day. Don't take the higher on-demand dose every day unless your prescriber tells you to.
Is generic sildenafil the same as Viagra?
Yes. Generic sildenafil contains the same medicine as Viagra and works in the same way. It usually costs much less.
Can I drink alcohol with sildenafil or tadalafil?
A small amount is usually fine. Heavy drinking makes it harder to get an erection and can make side effects such as dizziness worse.
Can I switch from sildenafil to tadalafil?
Yes, many men do. Speak to your prescriber first, and never take both on the same day.
Sources: