You should always consult with your primary care physician before taking any new medication, but here is a list of contraindications (when NOT to use a medication) for Viagra, according to wikipedia: Contraindications include (do not use Viagra...): * When taking nitric oxide donors, organic nitrites and nitrates, such as glyceryl trinitrate, sodium nitroprusside, amyl nitrite ( poppers )[5] * In men for whom sexual intercourse is inadvisable due to cardiovascular risk factors * Severe hepatic impairment (decreased liver function) * Severe impairment in renal function * Hypotension (low blood pressure) * Recent stroke or heart attack * Hereditary degenerative retinal disorders (including genetic disorders of retinal phosphodiesterases)