Re: Enhancement pills. Question about their mechanism.
I can only speak for Viagra (sildenafil). There are a number of things going on in your body for and during an erection. You become aroused and extra blood rushes to your penis. Importantly, your penis then doesn't allow the blood to leave, which is what causes an erection. At a certain point, your body allows the blood to leave and all returns to normal. What sildenafil does is it tells your body NOT to release the blood that has entered your penis. It doesn't GIVE you an erection, you still need to get aroused on your own, it just allows you to keep it. It can seem like it gives you the erections or at least makes them harder because you seem to get it much easier, but chemically speaking, it only allows you to keep it.
Viagra is the only sildenafil available in the States as it's under patent protection. But outside of the U.S, sildenafil is readily available.