Sildenafil, sold under the brand name Viagra among others, is a medication used to treat erectile dysfunction and pulmonary arterial hypertension. It is also sometimes used off-label for the treatment of certain symptoms in secondary Raynaud's phenomenon. It is unclear if it is effective for treating sexual dysfunction in females. It can be taken orally, intravenously, or through the sublingual route. Onset when taken orally is typically within 20-45 minutes and in some patients, its effects may be felt in 12 minutes. Duration of action is at least four hours. However, in rare cases may last as long as 10 hours. By 24 hours, Sildenafil is either at a very low level or undetectable in the body.