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Viagra changed the way the world viewed impotence, now referred to as "erectile dysfunction."

Although there were several medications to treat this condition before Viagra, none were available in an oral formulation.

Caverject (alprostadil) has to be injected into the penis, something that causes many men to cringe. Swallowing a pill is a lot more appealing for most men.

Viagra has no aphrodisiac properties. It will not improve libido or cause an erection.

What it can do is facilitate an erection when a man is stimulated sexually. It does this by blocking an enzyme which allows the buildup of a chemical that improves blood flow into the penis.

The positive effect may be seen anywhere from 30 minutes to four hours after swallowing Viagra.

Side Effects and Interactions

Side effects associated with Viagra include headache, flushing or upset stomach.

Vision may also be affected, which may make it difficult to discriminate between blue and green.

Nasal congestion, diarrhea, dizziness, urinary tract infection and rash have also been reported.
Report any symptoms to your physician promptly.

Erections that last longer than four hours are rare but require emergency medical attention to avoid permanent damage to the penis.

Nitroglycerin (under brand names such as Minitran, Nitro-Bid, Nitro-Dur, Nitrogard, Nitrolingual, Nitrong, Nitrostat, Transderm-Nitro) and nitrate-based heart and blood pressure medicines such as Imdur, ISMO, Isordil, Monoket and Sorbitrate are incompatible with Viagra.

Erythromycin, Nizoral, Sporanox, Tagamet, AIDS medicines such as ritonavir or saquinavir and grapefruit or grapefruit juice may increase blood levels of Viagra.

Rifampin and St. John's wort are expected to reduce blood levels of this medicine.

Taking Viagra and Norvasc (amlodipine) together might lower blood pressure more than expected.

It's possible that flavonoids found in the herb Echinacea affect the enzyme (CYP 3A4) responsible for metabolizing many common drugs. If so, medications such as Viagra could reach higher levels in the body.

The herb St. John's wort might speed elimination of Viagra from the body, which could reduce its effectiveness.

Check with your pharmacist and physician to make sure Viagra is safe in combination with any other medicines and herbs you take.

Special Precautions

Viagra is not an all-purpose solution to sexual dysfunction. The prescribing physician will need to conduct an examination and take a thorough medical history to make sure Viagra is appropriate.

Men over 65 and those with kidney or liver problems may require lower doses of Viagra.

Viagra should be avoided by men taking medications such as nitroglycerin, Imdur, ISMO, Isordil, Monoket, Sorbitrate or other nitrates, as it could interact with these medicines in a potentially lethal manner. See "

Side Effects and Interactions

" below.

Many men have died while taking Viagra. Some of these deaths are attributed to interactions or unaccustomed physical exertion, but others are unexplained.

The medication may be especially dangerous for men with heart conditions.

Those who have a history of heart problems, including angina, irregular heart beats, heart failure or heart attack, should alert the physician before starting such therapy as it may be inappropriate.

Other conditions that call for special consideration include Peyronie's disease (bent penis), a history of stroke, high or low blood pressure, sickle cell anemia, multiple myeloma, leukemia, retinitis pigmentosa, stomach ulcers or bleeding problems.


Taking the Medicine

Viagra is taken approximately one hour before sexual activity, although it may start working within 30 minutes and remain effective up to four hours.

Taking the pill with a meal high in fat will delay its action.

Viagra should not be taken more than once daily.

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About the Author
Joe Graedon is a pharmacologist who has dedicated his career to making drug information understandable to consumers. His best-selling book, The People’s Pharmacy, was published in 1976 and led to a syndicated newspaper column, syndicated public radio show and web site. In 2006, Long Island University awarded him an honorary doctorate as “one of the country's leading drug experts for the consumer.” .
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