Sildenafil is used for the treatment of erectile dysfunction (male impotence). It helps to achieve and maintain an erection when sexual stimulation occurs. It does this by allowing a greater flow of blood into the penis when a man taking the medication is sexually aroused.

Your doctor may have suggested this medication for conditions other than the ones listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

The usual recommended dose is 50 mg taken, as needed, approximately one hour before sexual activity. However, the medication may be taken during a time frame between four hours to one-half hour before sexual activity. Based on the effectiveness and side effects of the medication, the dose may be increased to 100 mg or decreased to 25 mg. The maximum recommended dose is 100 mg and it is not recommended to take more than one dose per day. Do not take sildenafil with a high-fat meal as this may reduce the effectiveness of the medication.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones given here, do not change the way that you are taking the medication without consulting your doctor.

It is very important that this medication be taken exactly as prescribed by the doctor. Do not take higher doses of this medication than those prescribed by your doctor.

Viagra is available in strengths of 25 mg, 50 mg, and 100 mg.

25 mg: Each blue, round, diamond-shaped tablet, marked "PFIZER" on one side and "VGR 25"on the other side, contains sildenafil citrate 25 mg.

50 mg: Each blue, round, diamond-shaped tablet, marked "PFIZER"on one side and "VGR 50" on the other side, contains sildenafil citrate 50 mg.

100 mg: Each blue, round, diamond-shaped tablet, marked "PFIZER" on one side and "VGR 100" on the other side, contains sildenafil citrate 100 mg.

Nonmedicinal ingredients: anhydrous dibasic calcium phosphate, croscarmellose sodium, FD&C Blue No. 2 Aluminum Lake, hydroxypropyl methylcellulose, lactose, magnesium stearate, microcrystalline cellulose, titanium dioxide, and triacetin.

Sildenafil should not be taken by:

• anyone allergic to sildenafil or any of the ingredients of the medication
• anyone taking any type of nitrate medication or anyone who uses short-acting nitroglycerin medication (e.g., for relief of chest pain caused by angina) due to the risk of developing very low blood pressure which can be dangerous
• anyone for whom sexual activity is not advisable

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor. Your health professional may be able to help you to deal with some of the effects.

The following side effects may go away as your body becomes used to the medicine; check with your doctor if the following side effects continue or become bothersome.

More common:

• flushing
• headache
• nasal congestion
• stomach discomfort following meals

  Less common:

• diarrhea

  Rare:

• anxiety

Call your doctor as soon as possible if any of the following side effects occur:

Less common:

• abnormal vision, including blurred vision, seeing shades of colours differently than before, or sensitivity to light
• bladder pain
• cloudy or bloody urine
• dizziness
• increased frequency of urination
• pain on urination

  Rare:

• bleeding of the eye
• convulsions (seizures)
• decreased vision or other changes in vision
• double-vision
• prolonged, painful, or inappropriate erection of penis
• redness, burning, or swelling of the eye
• vision loss (temporary)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Prolonged erection: If an erection lasts longer than four hours (a rare occurrence), seek immediate medical assistance. If this condition is not treated quickly, tissue damage and permanent loss of potency could result.

Vision problems: A small percentage of people taking this medication have trouble with vision (e.g., blurred vision, light sensitivity, inability to distinguish colour). If this happens, do not drive or operate heavy machinery until this effect goes away.

Children: Children should not use sildenafil.

Pregnancy and breast-feeding: Sildenafil is not approved for use by women.

• cimetidine
• erythromycin
• itraconazole
• ketoconazole
• nitrates
• rifampin
• protease inhibitors (e.g., indinavir, nelfinavir, ritonavir, saquinavir)

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. In many cases, interactions are intended or are managed by close monitoring. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than the ones listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications that you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.