Viagra tablets contain the active ingredient sildenafil, which is a type of medicine called a phosphodiesterase type 5 inhibitor. It is used in the treatment of erectile dysfunction (impotence) to help men achieve and maintain an erection.
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.
Sildenafil 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, which improves blood flow to the penis and helps maintain an erection.
As sildenafil only enhances the actions of the chemical messengers responsible for producing an erection, it will only work once these messengers are released in the penis. This means that sexual stimulation is required for it to produce and maintain an erection.
Viagra tablets should preferably be taken on an empty stomach. If they are taken with food they may take longer to start working.
Your tablet should be swallowed whole with a drink of water.
Your Viagra tablet should be taken about one hour before sexual activity. With sexual stimulation you may achieve an erection after about 30 to 60 minutes.
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.
You should not take Viagra more than once a day.
Medicines and their possible side effects can affect individual people in different ways. Just because a side effect is stated here does not mean that all people using this medicine will experience that or any side effect. The following are some of the side effects that are known to be associated with Viagra:
Common (affect between 1 in 10 and 1 in 100 people):
- Nasal congestion.
- Indigestion (dyspepsia).
Uncommon (affect between 1 in 100 and 1 in 1000 people):
- Awareness of your heart beat (palpitations).
- Increased heart rate (tachycardia).
- Chest pain.
- Muscle pain.
- Sleepiness or fatigue.
- Decreased sensation of the body to normal stimulation such as touch or pain.
- Sensation of spinning.
- Sensation of ringing or other noise in the ears (tinnitus).
- Feeling sick or vomiting.
- Dry mouth.
- Eye disorders such as bleeding at the back of the eye, bloodshot eyes/red eyes, eye pain, double vision, abnormal sensation in the eye.
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 Viagra, please read the information provided with the medicine or consult your doctor or pharmacist.
Viagra should be used with caution in:
- Elderly people
- Decreased kidney function.
- Decreased liver function.
- Disease involving the heart and blood vessels (cardiovascular disease).
- Conditions such as sickle cell disease, bone marrow cancer (multiple myeloma) or leukaemia, in which there is an increased risk of prolonged erections (priapism).
- People with any obstruction of blood flow out of the heart, e.g. due to narrowing of the aorta (aortic stenosis).
- Bleeding disorders, e.g. haemophilia.
- People with an active peptic ulcer.
- Men with a physical abnormality of the penis, such as severe curvature, scarring or Peyronie's disease.
Viagra should NOT be used in:
- Children and adolescents under 18 years of age.
- Conditions in which sexual activity is not advisable, for example severe heart disorders.
- Men with angina not well controlled by medical treatment (unstable angina).
- Men with angina that occurs during sex.
- Men who have had a heart attack in the last three months.
- Men who have had a stroke in the last six months.
- Men with mild to severe heart failure in the last six months.
- People with low blood pressure (hypotension).
- Severely decreased liver function.
- Hereditary degeneration of the back of the eyeball (retina), such as retinitis pigmentosa.
- Men taking any form of nitrate medications, e.g. glyceryl trinitrate.
- Men 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 (Viagra tablets contain lactose).
This medicine should not be used if you are allergic to 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 Viagra and inform your doctor or pharmacist immediately.
The patient information leaflet (PIL) is a leaflet containing specific information about medical conditions, doses and side effects. You can download a copy of the PIL here:
Patient Info Leaflet