Prostaglandins (alprostadil): Alprostadil can be injected into the penis or inserted as a pellet through the urethra. It causes an erection without sexual stimulation that usually lasts about 60 minutes. The danger with this method is that too high a dose can cause priapism, an erection that won't go away. This condition requires immediate medical attention as it can cause serious bruising, bleeding, pain and permanent penile damage. Once the doctor is sure of the right dose, the man can self-inject at home.
If you just got off solo, you might have to wait before you can hop into bed with your partner, says Dr. Brahmbhatt. It might have something to do with a spike in the hormone prolactin after you orgasm, according to a study published in the International Journal of Impotence Research. This hormone has been linked to difficulties maintaining an erection or even ejaculating.
Sildenafil (Viagra) was the first oral phosphodiesterase type 5 (PDE5) inhibitor approved by the FDA in the United States for the treatment of erectile dysfunction (it is not approved for women). Sildenafil inhibits PDE5, which is an enzyme that destroys cGMP. By inhibiting the destruction of cGMP by PDE5, sildenafil allows cGMP to accumulate. The cGMP in turn prolongs relaxation of the smooth muscle of the corpora cavernosa. Relaxation of the corpora cavernosa smooth muscle allows blood to flow into the penis resulting in increased engorgement of the penis. In short, sildenafil increases blood flow into the penis and decreases blood flow out of the penis.