These are better known as phosphdiesterase type 5 inhibitors, or PDE-5 inhibitors (sildenafilcitrate - Viagra; vardenafil- Levitra; tadalafil-Cialis).  These medications are FDA approved for the treatment of men’s erectile dysfunction. 

When taking one of the above medications, a person has to wait 30 minutes to an hour to obtain a usable erection, which lasts for several to 36 hours. In this period of time, a man can achieve an erection in response to erotic stimulation – if this doesn’t exist, no erection will occur.

There are some precautions and side effects that need to be considered when using PDE-5 inhibitors. First of all, these shouldn’t be used by men that take nitrate-based medications like ISMO, Imdur, Nitro-Dur, Nitro-Paste, Nitrostat, Nitro-Bid, etc., because the combination can cause a massive reduction in blood pressure.  The reduction in blood pressure coupled with the cardiovascular stress of intercourse can lead to heart attacks or strokes in men that previously had vascular disease. These medications shouldn’t be used by men that had recent heart attacks, high blood pressure or heart disease without a proper medical evaluation.

Among the side effects of PDE-5 inhibitors are indigestion, dizziness, nasal congestion, headache, and also priapism (overly prolonged erection). Priapism can be damaging because while the penis is erect it doesn’t receive any oxygen. Thus, if a man’s erection lasts longer than four hours he should ask for medical treatment since an erection that lasts more than 24 hours will permanently damage the penis.