Erectile Dysfunction (ED, Impotence)

  • Medical Author:
    Charles Patrick Davis, MD, PhD

    Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

  • Medical Editor: Melissa Conrad Stöppler, MD
    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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Tadalafil (Cialis)

What is tadalafil (Cialis)?

Tadalafil (Cialis) is the third oral medicine approved by the U.S. FDA for the treatment of erectile dysfunction. Like sildenafil (Viagra) and vardenafil (Levitra), tadalafil inhibits PDE5 (as described earlier).

How effective is tadalafil (Cialis)?

The safety and efficacy of tadalafil in the treatment of erectile dysfunction was evaluated in 22 clinical trials involving more than 4,000 men. Seven of these trials were randomized, prospective, placebo-controlled studies of 12 weeks' duration. Two of these studies (involving 402 men) were conducted in the United States, and the other five studies (involving 1,112 men) were conducted outside the United States. Two of these trials were conducted in special populations with erectile dysfunction; one in men with diabetes mellitus, another in men who developed erectile dysfunction after nerve-sparing prostate cancer surgery.

Effectiveness of tadalafil in these studies was assessed using a sexual function questionnaire. Study participants also were asked if they were able to achieve vaginal penetration and to maintain erections long enough for successful intercourse.

In all seven trials, tadalafil was significantly better than placebo in improving men's ability to achieve and maintain erections. Improvements in erectile function was observed in some patients at 30 minutes after taking a dose; and improvements can last for up to 36 hours after taking Cialis when compared to placebo.

How should tadalafil (Cialis) be administered?

The recommended starting dose of tadalafil for most patients is 10 mg taken orally approximately one hour before sexual activity. The dose may be adjusted higher to 20 mg or lower to 5 mg depending on efficacy and tolerability. The maximum recommended dosing frequency is once per day, although for many patients tadalafil can be taken less frequently since the improvement in erectile function may last 36 hours. Tadalafil may be taken with or without food. Tadalafil is also available in 2.5 mg or 5 mg dosages for daily use.

What are the side effects of tadalafil (Cialis)?

Tadalafil is generally well tolerated with only mild side effects. The most common side effects reported include headache, indigestion, back pain, muscle aches, facial flushing, and nasal congestion.

Back pain and muscle aches occurred in less than 7% of patients and usually occurred 12 to 24 hours after taking tadalafil. The back pain and muscle aches associated with tadalafil were characterized by mild to moderate muscle discomfort in the lower back, buttocks, and thighs, often aggravated by lying down. The back and muscle aches resolved in most patients without treatment within 48 hours. When treatment was necessary, acetaminophen (Tylenol) and nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen (Motrin, Advil) or naproxen (Aleve) were effective. Approximately 0.5% of all the patients using tadalafil discontinued the drug due to back pain or muscle aches.

Reports of abnormal vision were rare; it occurred in less than 0.1% of patients using tadalafil.

There have been rare reports of priapism (prolonged and painful erections lasting more than 6 hours) with the use of oral PDE5 inhibitors such as vardenafil, sildenafil, and tadalafil. Men with blood cell diseases such as sickle cell anemia, leukemia, and multiple myeloma have higher than normal risks of developing priapism. Untreated priapism can cause injury to the penile tissue and lead to permanent loss of potency. If there is prolonged erection (longer than 4 hours), immediate medical assistance should be sought.

Who should not use tadalafil (Cialis)?

Tadalafil can cause hypotension (abnormally low blood pressure, which can lead to fainting and even shock) when given to patients who are taking nitrates. Patients taking nitrates daily should not take tadalafil. Most commonly used nitrates are medications to relieve angina (chest pain due to insufficient blood supply to heart muscle because of narrowing of the coronary arteries). These include nitroglycerine tablets, patches, ointments, sprays, pastes, and isosorbide dinitrate and isosorbide mononitrate. Other nitrates such as amyl nitrate and butyl nitrate are found in some recreational drugs called poppers.

Tadalafil should not be used with alpha-blockers (except Flomax), medicines used to treat high blood pressure and benign prostate hypertrophy (BPH) because the combination of tadalafil and an alpha-blocker may lower the blood pressure greatly and lead to dizziness and fainting. Examples of alpha-blockers include tamsulosin (Flomax), terazosin (Hytrin), doxazosin (Cardura), alfuzosin (Uroxatral), and prazosin (Minipress). The only alpha-blocker that can be used safely with tadalafil is tamsulosin (Flomax). When tadalafil (20 mg) was given to healthy men taking 0.4 mg of Flomax daily, there was no significant decrease in blood pressure and so patients on this dose of tamsulosin (Flomax) can be prescribed tadalafil. The only alpha-blocker that has not been tested with tadalafil is alfuzosin (Uroxatral) and no recommendations can be made regarding the interaction between the two.

Tadalafil is not recommended for men with the following conditions:

  • Unstable angina (chest pain due to coronary artery disease that occurs at rest or with minimal physical exertion)
  • Low blood pressure (a resting systolic blood pressure less than 90 mm Hg)
  • Uncontrolled high blood pressure (greater than 170/110 mm Hg)
  • Recent stroke or heart attack (within six months)
  • Uncontrolled, potentially life-threatening abnormal heart rhythms
  • Severe liver disease
  • Severe heart failure or disease of the heart valves (for example, aortic stenosis)
  • Retinitis pigmentosa

Therefore, men with these conditions should not use tadalafil without having these conditions evaluated and stabilized first. For example, men with uncontrolled high blood pressure should have their blood pressure controlled; and men with potentially life-threatening abnormal heart rhythms should have these rhythms controlled.

When there is angina or heart failure, the doctor may need to determine whether the heart has enough reserve to safely carry out the work necessary for sexual activity by performing cardiac treadmill stress testing.

What precautions should be taken when using tadalafil?

In most healthy men, some of the drug will remain in the body for more than two days after a single dose of tadalafil. Metabolism (clearing of the drug from the body) of tadalafil can be slowed by liver disease, kidney disease, and concurrent use of certain medications (such as erythromycin, ketoconazole, and protease inhibitors). Slowed breakdown allows tadalafil to stay in the body longer and potentially increase the risk for side effects. Therefore, the dose and frequency of tadalafil has to be lowered in the following examples:

  • Medications such as erythromycin, ketoconazole (Nizoral), itraconazole (Sporanox), ritonavir (Norvir), and indinavir (Crixivan) can slow the breakdown of tadalafil. Therefore men taking these medications should not take more than 10 mg of tadalafil and should not take tadalafil more frequently than every 72 hours.
  • No tadalafil dose adjustment is necessary for men with only mild kidney disease. Men with moderately severe kidney impairment should start tadalafil at 5 mg every 24 hours and not to exceed the maximum dose of 10 mg taken every 48 hours. In men with severe kidney disease and on dialysis, the maximum dose should not exceed 5 mg.
  • Men with severe liver disease should not take tadalafil. Men with mild to moderate liver disease should not exceed tadalafil dose of 10 mg once daily.
Medically Reviewed by a Doctor on 2/25/2016

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