How Does Cialis Work?
Many people wonder, "How does Cialis work?" Cialis works by blocking PDE5, the chemical that reverses an erection. When this chemical is blocked, the arteries in the penis are able to open wider so that more blood can flow into the penis. Cialis can start working in as little as 30 minutes, and can work up to 36 hours from the time you take your dose. Because Cialis has no effect on the chemicals that cause an erection (it simply keeps them in the penis longer), it does not work without stimulation.
How Does Cialis Work? — An Introduction
Cialis ® (tadalafil ) is a medication that has been licensed to treat erectile dysfunction. which is the repeated inability to get or keep an erection firm enough for sexual intercourse. It is also approved for treating enlarged prostate symptoms .
Cialis is very effective at treating erectile dysfunction. The medication works by allowing the arteries in the penis to open wider so more blood can flow into the penis. This results in an improved erection. For an enlarged prostate. it probably works by relaxing the prostate and the bladder.
Understanding Erections and Erectile Dysfunction
To understand how Cialis works, it may be helpful to understand erections.
When a man is aroused, nerve signals are sent from the brain and around the penis. These nerve signals cause chemicals to be released that relax the muscles in the penis. Normally, these muscles are constricted so that blood cannot flow into the penis. When these muscles relax, large amounts of blood are able to enter the penis, causing an erection. An erection is reversed when another chemical (known as phosphodiesterase type 5 [PDE5]) breaks down the chemicals that caused the muscles to relax in the first place. This causes the muscles in the penis to constrict again as blood leaves the penis.
Comparison of Viagra, Levitra and Cialis
Male sexual dysfunction is one of the most common health problems affecting men and is more common with increasing age. Chronic ED affects about 5% of men in their 40s and 15пїЅ25% of men by the age of 65. Transient ED and inadequate erection affect as many as 50% of men between the ages of 40 and 70.
In around 95% of the cases, a satisfactory treatment can be found. Erectile dysfunction is treatable at any age, and awareness of this fact has been growing. More men have been seeking help and returning to normal sexual activity because of improved, successful treatments for erectile dysfunction.
Three PDE-5 inhibitors
Currently, there are three oral medications approved by the FDA for the treatment of erectile dysfunction: sildenafil (Viagra), vardenafil (Levitra), and tadalafil (Cialis). They block the enzyme phosphodiesterase type 5 (PDE-5) and belong to a class called phosphodiesterase (PDE) inhibitors.
Since introduction of the first PDE-5 inhibitor Viagra, there has been a fundamental change in the treatment of erectile dysfunction. Although there are a number of options available for non-surgical treatment, it is clear that oral therapy has revolutionized the treatment approach to patients with erectile dysfunction. The development of the PDE-5 inhibitors Levitra and Cialis prompts the question of whether and how these sexual medications differ in terms of their efficacy and adverse effects.
Viagra was the first and is probably the most famous of the three PDE-5 inhibitors used to treat erectile dysfunction. Viagra was approved for erectile dysfunction in March 27, 1998. Viagra is manufactured by Pfizer, Inc.
Levitra was the second PDE-5 inhibitor to come to market in the United States, and it was approved by the FDA in August 19, 2003. Levitra is manufactured by Bayer Pharmaceuticals Corporation.
Cialis was the third PDE-5 inhibitor to come to market in the United States and was approved by the FDA at the end of November 21, 2003. Cialis is manufactured by Lilly ICOS LLC.
The major advantage of these medications for sexual enhancement is that they do not cause an erection at inappropriate times, because they act only in response to sexual stimulation. If there is no sexual stimulation drug remains in the background. All three are taken orally prior to planned sexual activity, acting to increase blood flow in the penis in response to sexual stimulation. However, there are important differences between the three, differences that could influence safety, specificity, duration of action, adverse effects, and ultimately, public acceptance within this class.
back pain, muscle aches, nasal congestion, facial flushing, dizziness
Mechanism of action
Sildenafil, vardenafil, and tadalafil do not directly cause an erection of the penis, but they alter the body’s response to sexual stimulation by enhancing the effect of the nitric oxide, a chemical that is normally released during stimulation. Nitric oxide causes relaxation of the muscles in the penis, which allows for better blood flow to the penile area.
All PDE-5 inhibitors have demonstrated excellent efficacy in general and in specific populations (eg, men with diabetes mellitus or those who have undergone radical prostatectomy). Viagra, at 84%, is slightly more effective than Levitra at 80% and Cialis at 81%.
Viagra and Levitra differ only minimally in terms of their structure, while Cialis differs markedly from Viagra and Levitra in terms of its molecular structure, which is also reflected in pharmacokinetic differences.
- Viagra. 25 mg, 50 mg 100 mg tablets
- Onset of action. 30 minutes (effect delayed if taken with food)
- Duration of action. 4 to 5 hours
- Levitra. 2.5 mg, 5 mg, 10 mg, 20 mg tablets
- Onset of action. 25 minutes (effect delayed by fatty meal)
- Duration of action. 4 to 5 hours
- Cialis. 5 mg, 10 mg, 20 mg tablets
- Onset of action. 16-45 minutes (effect NOT delayed by food)
- Duration of action. 36 hours
Viagra does not work as well as it would otherwise if you eat a high-fat meal around the time you take it. Viagra should be taken on an empty stomach. Levitra may be slightly less effective if you eat a high-fat meal, but a moderate-fat meal does not reduce its effectiveness. Cialis works without regard to what you eat.
Viagra and Levitra have similar half-lives, and onset and duration of action. Cialis has a slower onset of action and longer duration of action, which is attributed to its longer half-life.
Men who wish for spontaneity may opt for Cialis, which may allow for successful intercourse up to 36 hours postdose, even though it takes longer to reach peak effect. The considerably longer duration of effect for Cialis will likely allow less frequent dosing and greater impulsiveness between partners, but also could potentially prolong adverse effects.
PDE-5 inhibitors are primarily excreted via the fecal route with varying percentages eliminated renally.
The recommended dose for Viagra is 50 mg, and the physician may adjust this dose to 100 mg or 25 mg, depending on the patient.
The recommended dose for either Levitra or Cialis is 10 mg, and the physician may adjust this dose to 20 mg if 10 mg is insufficient. A lower dose of 5 mg is available for men who take other medicines or have conditions that may decrease the body’s ability to use the drug. Levitra is also available in a 2.5 mg dose.
None of these PDE-5 inhibitors should be used more than once a day.
Most common side effects:
- Viagra. headache, epistaxis, flushing, indigestion, dizziness, nasal congestion, abnormal vision
- Levitra. headache, flushing, indigestion, nausea, dizziness, nasal congestion
- Cialis. headache, indigestion, back pain
PDE-5 inhibitors are generally well tolerated. Side effects include headache, flushing, dyspepsia, and nasal congestion.
Visual abnormalities are encountered with Viagra, but are less likely with Levitra and unlikely with Cialis. Flushing and dyspepsia that are associated with Viagra and Levitra are less common with Cialis. Back pain and muscle aches (myalgia) may occur with Cialis, but are unusual with either Viagra or Levitra. Side effects of Cialis tend to last longer, but are less marked than with the other drugs.
Precautions and contraindications
All PDE-5 inhibitors are absolutely contraindicated in persons who take organic nitrates, because they induce vasodilation.
The FDA no longer considers concomitant use of alpha-blockers a contraindication to use of PDE-5 inhibitors. However, persons on alpha-blockers must be on a stable dose of alpha-blocker prior to using a PDE-5 inhibitor.
Since both Viagra and Levitra have moderate vasodilatory and hypotensive effects, they should not be given in the presence of marked arterial or orthostatic hypotension, and should only be administered with caution in aortic stenosis or hypertrophic obstructive cardiomyopathy.
Men who have had a heart attack or stroke within the past 6 months and those with certain medical conditions (e.g. uncontrolled high blood pressure, severe low blood pressure or liver disease, unstable angina) that make sexual activity inadvisable should not take Cialis. Dosages of the drug should be limited in patients with kidney or liver disorders.
The differences between the 3 drugs are not great. All appear to be effective and safe. Levitra has less side effects compared to Viagra and lasts about the same time as Viagra in the body. Cialis has few side effects and lasts longer in the body to increase spontaneity than either Levitra or Viagra and there is no reduction in absorption when Cialis is taken with food. However, the longer half-life imposes increased risk for drug interactions.
- 1. The Merck Manual of Medical Information. Mark H. Beers et al. eds. 2nd Home Edition. Whitehouse Station, NJ: Merck; 2003.
- 2. Doggrell SA. Comparison of clinical trials with sildenafil, vardenafil and tadalafil in erectile dysfunction. Expert Opin Pharmacother. 2005 Jan;6(1):75-84.
- 3. Viagra Prescribing Information PDF
- 4. Levitra Prescribing Information PDF
- 5. Cialis Prescribing Information PDF
Published: May 05, 2007
Last updated: March 24, 2016
Cialis vs. Levitra vs. Viagra: How Each Stacks Up
Three of a kind?
Cialis, Levitra, and Viagra are oral medications used to treat erectile dysfunction (ED). You may also know them by their generic names, tadalafil (Cialis), vardenafil (Levitra), and sildenafil (Viagra).
About 30 million men occasionally have a problem with getting or keeping an erection, according to the Urology Care Foundation. When ED becomes a problem, many men turn to oral ED medications. These drugs often help. Cialis, Levitra, and Viagra each work in similar ways. But there are also some differences, such as when you take them, how long they work, and what their side effects are.
Cialis. Levitra. and Viagra are all in a class of drugs called PDE-5 inhibitors. These drugs work by blocking an enzyme called phosphodiesterase type 5. They also boost a chemical in your body called nitric oxide. This action encourages the muscles in your penis to relax. Relaxed muscles allow blood to flow freely so that when youвЂ™re aroused, you can get an erection. It also helps you maintain the erection long enough to have sex.
Levitra and Viagra stay in your bloodstream for about four to six hours. Cialis remains in your bloodstream for 17 to 18 hours or longer. The length of time a drug stays in your system may be important if youвЂ™re taking other medications.
Here are more basics on each of these drugs:
Be sure to take this drug exactly as your doctor tells you to. If you have questions or concerns, talk with your doctor.
Cost, availability, and insurance
Cialis, Levitra, and Viagra are usually stocked at most pharmacies. All three of these drugs cost about the same amount. In general, most health insurance companies wonвЂ™t cover their costs. But if you have certain medical conditions, your health plan may pay for the drug with prior authorization.
The side effects of these medications are similar. Most men have only mild side effects.
The chart below compares the side effects of these drugs.
Tell your doctor if you have any side effects that linger and donвЂ™t go away on their own. If you have an erection that lasts longer than four hours, call your doctor right away.
Each drug comes with the chance of drug interactions. Since PDE-5 inhibitors work on the body in similar ways, Cialis, Levitra, and Viagra come with similar interactions.
If you have an erection that lasts longer than four hours, call your doctor right away.
All three of these drugs interact with nitrates. They also all interact with blood pressure drugs such as alpha-blockers. For Cialis, these also include the drugs bendrofluazine, enalapril. and metoprolol. For Viagra, these also include the blood pressure drug amlodipine .
Viagra also interacts with the drug ritonavir .
Cialis can also interact with alcohol. Drinking alcohol with Cialis can cause low blood pressure when you stand up from a sitting or lying position. This may result in dizziness or a headache. To learn more, read more about the effects of mixing Cialis and alcohol.
Levitra and Viagra do not seem to cause low blood pressure when taken with alcohol. However, alcohol may interfere with your ability to get an erection, even while youвЂ™re taking any of these drugs.
If you have ED, talk to your doctor about Cialis, Levitra, and Viagra. Tell your doctor if you take other over-the-counter or prescription drugs or supplements. Be sure to mention all other health conditions you have.
Each of these three popular drugs has been shown to help men with ED when theyвЂ™re used correctly. All three drugs have good results, but it may take a little time and patience to get it right. If one drug doesnвЂ™t work or produces unpleasant side effects, you can try another drug. It may also take some trial and error to find the dosage that works best for you. And if youвЂ™re not sure that drug treatment is right for you, you can give these natural treatments for erectile dysfunction a try.
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