Side Effects Can Be Bothersome
According to pre-marketing clinical trials, 2.5% of those taking Viagra discontinued use because of side effects compared to 2.3% of those taking a placebo. The effects were generally mild to moderate in nature and lasted for only a short time.
The following are reported side effects (when taking Viagra as recommended on an as-needed basis): headache, flushing, dyspepsia, nasal congestion, urinary tract infection, abnormal vision, diarrhea, dizziness, and rash. Headache, flushing, and dyspepsia (upset stomach) were the most common. Vision problems were mild and transient (mostly color tinge to vision but also blurred vision and sensitivity to light).
In rare cases, a sudden decrease or loss in hearing or vision in one or both eyes have been reported. It is unsure if Viagra has any level of responsibility for these occurrences. If these complications do occur, stop taking Viagra and notify your health care provider right away.
There have also been rare instances of erections lasting many hours. This can cause permanent damage if it is not treated right away. Seek immediate medical attention if an erection lasts longer than 4 hours.