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Last updated October 10, 2019. 4 minute read

What's the difference between Cialis and Viagra?

Viagra (sildenafil) and Cialis (tadalafil) can be effective in as little as 1 hour, though for some patients, these medicines can work more rapidly. Sildenafil will work reliably for 6–8 hours, but tadalafil will work for up to 36 hours.

Written by Health Guide
Reviewed by Dr. Jefferson Chen, MD

Weighing the benefits and risks of Cialis versus Viagra requires some basic knowledge of each. A brief comparison of Viagra versus Cialis can be made by examining how they can be used (“as needed” for either or daily for Cialis), the time it takes for them to work, the length of time they continue to work, and the side effects each of them might cause.

Vitals

  • Viagra (sildenafil) and Cialis (tadalafil) can be effective in as little as 1 hour, though for some patients, these medicines can work more rapidly.
  • Sildenafil will work reliably for 6–8 hours, but tadalafil will work for up to 36 hours.
  • To find out which medication may be right for you, talk with your healthcare provider.

Yet, one issue is rarely the sole factor men consider when taking a medication for erectile dysfunction. It is the interplay between a man’s social circumstances (and that of their partner), his need for a rapid onset of medication activity versus a prolonged duration of action, the individual reaction to the drug in terms of side effects, a person’s prior medical history, the other medications they take, and the very personal definition of what it means to achieve an erection satisfactory for sexual activity.

How Viagra and Cialis work

Viagra and Cialis are part of a family of medications called PDE-5 inhibitors. PDE-5 (phosphodiesterase type-5) is an enzyme that’s the bouncer of the reproductive system: It curtails an erection by hustling blood out of the penis (through a chain reaction involving other molecules). Viagra and Cialis work by blocking PDE-5. This maintains elevated levels of a substance known as cGMP, which relaxes smooth muscle and encourages blood vessels to widen. That makes blood flow more freely, including to the penis.

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Viagra vs. Cialis

Viagra and Cialis can be effective in as little as 1 hour, though for some patients, these medicines can work more rapidly.

Viagra leaves the body in about 6 to 8 hours, while Cialis can work for 24 to 36 hours. Nevertheless, the effect of a medication may not be needed beyond 6 or 8 hours, and any side effects (in addition to any positive effect) they cause will fade rapidly as the medication leaves the bloodstream. That means that someone who experiences nasal congestion or flushing when they use either Cialis or Viagra may find it useful to take the shorter acting medication, Viagra.

The length of time a medicine works is important to some. Let’s consider two men. One might be able to predict when sexual activity will occur. A drug that works rapidly and leaves his system quickly thereafter would be perfect, as with Viagra. Another man might know sex will occur during the course of a weekend but cannot know exactly when that will occur. For him, a drug with a prolonged period of activity is far more important than how long it takes for a medicine to start working. He would prefer Cialis. Also, Cialis can be taken in a low daily dose, and for a solid subset of patients, this is preferred.

Side effects of Viagra and Cialis

Common side effects of Viagra and Cialis include dizziness, headache, flushing, upset stomach or indigestion, blurred vision, changes in vision color, flu-like symptoms (such as a runny or stuffy nose or sore throat), memory problems, muscle or back pain, insomnia, or abnormal ejaculation.

Less common side effects of Viagra and Cialis include priapism (a prolonged erection that won’t go away), heart attack-like symptoms, eye problems such as sudden vision loss, ringing in ears or hearing loss, seizures, or swelling in the extremities.

The side effects you experience might determine whether Viagra or Cialis is the right choice for you. For example, if you experience a flushed face or headache when you use Cialis, you might find the shorter-acting medication, Viagra, to be a better option.

But do not take Viagra or Cialis if you:

  • Take nitrates or alpha-blockers
  • Have high blood pressure or low blood pressure
  • Take riociguat for pulmonary arterial hypertension
  • Are allergic to sildenafil or tadalafil or any of the inactive ingredients in Viagra or Cialis
  • Are not healthy enough for sexual activity

Don’t use Viagra or Cialis with amyl nitrate (poppers). That can cause an unsafe drop in blood pressure that can be fatal.
If you experience side effects while taking Viagra or Cialis, talk to your doctor right away. You should stop using Viagra or Cialis and seek immediate medical help if you experience:

  • Sudden vision loss in one or both eyes
  • Sudden decrease or loss in hearing
  • Chest pain, dizziness, or nausea during sex
  • An erection lasting longer than four hours (priapism)

Before taking Viagra, Cialis, or any ED medication, talk with your healthcare provider about possible side effects and whether you’re healthy enough for sex.

Other ED medications

Two other medications for ED are Levitra (vardenafil) and Stendra (avanafil). These drugs are also PDE-5 inhibitors and they work in a similar way as Viagra and Cialis. Stendra can be taken as soon as 15 minutes before sexual activity.

Other ED strategies

There are also lifestyle changes you can make that might improve ED. Those include losing weight, getting more exercise, changing your diet and stopping or reducing your use of tobacco, alcohol, and drugs. Read more about 11 all-natural ways to protect your erection here.

But if you’re experiencing ED, it’s important to talk with a healthcare provider about it. ED isn’t only caused by PDE-5 gone rogue. It can be a sign of a serious medical condition, such as heart disease, depression or a low testosterone level.