Duration of action
Viagra is ingested orally (through the mouth) and swallowed whole. Viagra is absorbed very quickly by the body, which is why it can start working within half an hour after ingestion. Usually, Viagra works best about one hour after ingestion.
After 4 hours, its effect is halved. After 8 hours, you will hardly notice anything and after 24 hours, Viagra will have left your body.
Viagra has a half-life of about 4 hours.