An erection is produced via a complex chain of events, involving signals from the nervous system and the release of chemical messengers within the tissues of the penis. One of these chemical messengers is called cyclic GMP.
Cyclic GMP causes the blood vessels in the penis to widen by relaxing a thin layer of muscle found in the blood vessel walls. This allows more blood to enter the penis, which ultimately results in the penis becoming rigid and erect.
Cyclic GMP is normally broken down by another chemical in the body called phosphodiesterase type 5. Tadalafil works by preventing the action of phosphodiesterase type 5, thus stopping the breakdown of cyclic GMP. This means that the blood vessels are kept dilated for longer, improving blood flow to the penis and maintaining an erection.
As tadalafil enhances the actions of the chemical messengers responsible for producing an erection, it will only work once these messengers are present. This means that sexual stimulation is required for it to produce and maintain an erection.
Cialis 10mg and 20mg tablets are intended for use on an 'as needed' basis. With these strength tablets the dose should be taken at least 30 minutes before intended sex. One dose can produce an erection in response to sexual stimulation for up to 36 hours. However, Cialis 10mg and 20mg tablets should be taken no more than once a day, and should not be taken every day on a continuous basis.
If Cialis 10mg or 20mg tablets work for you, but you anticipate taking Cialis on a regular basis (to have sexual activity at least twice a week), Cialis once-a-day tablets may be an appropriate option for you. These tablets contain a lower dose of tadalafil (2.5mg or 5mg) and are designed to be taken once a day, every day, allowing you to get an erection and have sex whenever you wish. Cialis 2.5mg and 5mg tablets should not be taken more than once a day.
What is it used for?
Impotence (erectile dysfunction).
This medicine may cause dizziness and so may affect your ability to drive or operate machinery safely. Do not drive or operate machinery until you know how this medicine affects you and you are sure it won't affect your performance.
If this medicine is taken with alcohol it may cause a drop in blood pressure that might make you feel dizzy. In addition, alcohol can impair sexual performance.
You should avoid drinking grapefruit juice while taking this medicine, as it may increase the level of this medicine in your blood and hence increase the risk of side effects.
If your erection lasts longer than four hours (priapism), consult a doctor immediately. Treatment of this condition should not be delayed more than six hours, as this can cause damage to the erectile tissue in the penis and irreversible erectile dysfunction.
If you experience a sudden, partial decrease or loss of vision in one or both eyes you should stop taking this medicine and consult your doctor immediately.
Use with caution in
Decreased kidney function.
Decreased liver function.
Disease involving the heart and blood vessels (cardiovascular disease).
People taking medicines for high blood pressure (see end of factsheet for more information).
Conditions such as sickle cell disease, bone cancer (multiple myeloma) or leukaemia, in which there is an increased risk of prolonged erections (priapism).
Physical abnormality of the penis, such as severe curvature, scarring or Peyronie's disease.
Not to be used in
Children and adolescents under 18 years of age.
Conditions in which sexual activity is not advisable, for example severe heart disorders.
Angina not well controlled by medical treatment (unstable angina).
People with angina that occurs during sex.
People who have had a heart attack in the last three months.
People who have had a stroke in the last six months.
People with mild to severe heart failure in the last six months.
Abnormal heart beats (arrhythmias) not controlled by treatment.
Uncontrolled high blood pressure (hypertension).
Low blood pressure (hypotension).
People taking any form of nitrate medications, eg glyceryl trinitrate (see end of factsheet for more examples).
People who have ever experienced an eye condition called non-arteritic anterior ischemic optic neuropathy (NAION). This condition causes a sudden, partial decrease or loss of
vision in one or both eyes due to damage to the optic nerve. It can be temporary or permanent. Talk to your doctor if you have ever experienced this.
Rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption (Cialis tablets contain lactose).
Cialis once-a-day dosing is not recommended for men with severely decreased kidney function or kidney failure.
This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.
Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Just because a side effect is stated here does not mean that all people using this medicine will experience that or any side effect.
Very common (affect more than 1 in 10 people):
Common (affect between 1 in 10 and 1 in 100 people):
Awareness of your heart beat (palpitations).
Pain in the muscles (myalgia).
Uncommon (affect between 1 in 100 and 1 in 1000 people):
Swelling of the eyelids.
Increased heart rate (tachycardia).
Increase in blood pressure (hypertension).
Decrease in blood pressure (hypotension). This is more common in men taking medicines to treat high blood pressure (antihypertensives).
Rash or hives.
Rare (affect between 1 in 1000 and 1 in 10,000 people):
Prolonged erections (see warning section above).
Swelling of the face.
Heart attack, stroke or mini-stroke (in most cases these events were reported in men who had pre-existing risk factors for heart disease).
The side effects listed above may not include all of the side effects reported by the medicine's manufacturer.For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.
How can this medicine affect other medicines?
It is important to tell your doctor or pharmacist what medicines you are already taking, including those bought without a prescription and herbal medicines, before you start taking this medicine. Similarly, check with your doctor or pharmacist before taking any new medicines while taking this one, to ensure that the combination is safe.
Tadalafil must not be taken with any form of nitrate medication, as this combination can produce a severe drop in blood pressure that can cause dizziness, fainting, or even a heart attack. Nitrate medications include the following:
glyceryl trinitrate, isosorbide mononitrate or isosorbide dinitrate, used for angina or heart failure
amyl nitrate (also known as 'poppers').
If tadalafil is taken by people who are taking medicines for high blood pressure (antihypertensives), the combination may potentially cause an extra drop in blood pressure. This is unlikely to be significant, but you should be aware that if it does occur it may make you feel dizzy. This is more likely to occur in people taking alpha-blocker medicines such as doxazosin, some of which are used to treat an enlarged prostate gland as well as high blood pressure. Tadalafil is not recommended for men taking doxazosin.
The use of tadalafil with other treatments for erectile dysfunction is not recommended, as the safety of such combinations has not yet been established.
The medicines listed below may reduce the breakdown of tadalafil by the liver, which could increase the risk of its side effects. Ask your doctor for advice if you are prescribed any of these, as you may need to take a lower tadalafil dose:
the antibiotic medicines clarithromycin and erythromycin
the antifungal medicines ketoconazole and itraconazole
the HIV protease inhibitors ritonavir and saquinavir.
The following medicines speed up the breakdown of tadalafil by the liver, and it could therefore be less effective in people taking any of these medicines:
If tadalafil is taken by people taking theophylline there may be a small increase in heart rate. This is unlikely to be significant, but you should tell your doctor if you are taking theophylline.