Viagra typically takes about 30 to 60 minutes to start working for most people, though it can sometimes take up to 2 hours. It works by improving blood flow to the penis but requires sexual arousal to be effective. The effects usually last around 4 to 6 hours, but this can vary depending on individual factors such as dosage, body weight, age, and other health conditions. Taking Viagra on an empty stomach can help it work faster, and heavy meals or grapefruit juice may delay or affect its action. It is recommended to take Viagra about an hour before sexual activity for best results.