Viagra (sildenafil citrate) is a prescription drug intended for the treatment of erectile dysfunction – a condition when the patient can’t have sex because of insufficient erection. Taking St.John’s wort along with Viagra has been reported to cause breakthrough bleeding, so make sure you let your health care provider know about taking this supplement. Nitrates can be found in recreational drugs (poppers) and a number of other medicines you may be taking for chest pain. They should never be combined or taken soon after Viagra as this can result in a dangerous drop in blood pressure when your heart will not be getting enough oxygen. Make sure you mention to your health care provider the fact of taking nitrates and do not take Viagra until at least two weeks after the last dose of nitrates pass.