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Frequently Asked Questions

Can you describe the role that ED (Erectile Dysfunction) drugs such as sildenafil (Viagra, Edegra), tadalafil (Cialis, Tadalis), or vardenafil (Levitra) play in sex?

Short Answer

In general, ED drugs help to achieve and maintain an erection by allowing increased blood flow into the penis over a longer period of time.

Long Answer

There are four stages in the human sexual response, as described by William H. Masters and Virginia E. Johnson in their book, The Human Sexual Response, released in 1966. They are:

  1. Excitement
  2. Plateau
  3. Orgasmic
  4. Resolution
Excitement Phase
This is also referred to as the Arousal Phase. There are many things that can start the excitement stage. For example, looking at a beautiful woman dressed in a sexy outfit, touching, foreplay, special thoughts, fantasies, or even dreams, can start the excitement stage. Also, pornography, erotica, masturbation, sexual role-playing and voyeurism can initiate this process. Once this stage begins, the brain takes this information and some physical changes start to occur in the body. Breathing speeds up, blood pressure rises slightly, the heart starts to beat a little faster, there may be a flushing effect on the skin, pupils may dilate (grow larger), and the penis starts to fill with blood and become partially erect. It is during this phase that the body starts to prepare for sexual intercourse.
Plateau Phase
This is the period of sexual excitement prior to orgasm. Sexual pleasure increases with stimulation and the heart rate may go up even more. The bladder closes, in order to prevent urine from mixing with the semen, and the muscles at the base of the penis begin to contract. Some seminal fluid may start to secrete from the penis.
Orgasmic Phase
Orgasm is the conclusion of the plateau phase and is a rapid release of sexual tension. Orgasms are often associated with other involuntary actions, including vocalizations and muscular spasms in other areas of the body. Also, a generally euphoric sensation is associated with orgasm. Orgasm may cause tiredness, and both males and females often feel a need to rest afterwards. This is attributed to the release of endorphins during orgasm, but can also be due to the body's need for a short rest after a bout of vigorous activity.
Resolution Phase
This phase occurs after orgasm and allows the muscles to relax. For men, there is a time after orgasm that an erection cannot occur, called the refractory period. The length of time varies from man to man. It should be noted that some women do not experience this refractory period, which allows for multiple orgasms.

Conclusion

  • Sexual stimulation causes the brain to send a message to the area of the penis, causing a release of nitric oxide (NO). This starts the erection process.
  • Viagra (sildenafil) and Cialis (tadalafil) are specific inhibitors of the phosphodiesterase 5 (PDE5) enzyme.
  • Phosphodiesterase 5 destroys cGMP, which is very important in achieving and maintaining an erection. cGMP is released and activated by nitric oxide (NO).
  • Viagra or Cialis, by inhibiting the action of PDE5, allow cGMP to remain active and more plentiful, so that it can help to achieve and maintain the erection by allowing for increased blood flow into the penis over a longer period of time (less chance of getting soft). Viagra will do this for up to 4-8 hours and Cialis for up to 36 hours.
  • In young and healthy males there are individual differences in the amount of stimulation required and how long the erection is maintained.
  • As we age or become ill (with diseases such as diabetes, etc.), or have to use certain prescribed medications, this process can be altered and we may have trouble maintaining an adequate erection. In many cases, the new ED drugs (like Viagra and Cialis) allow for a better and longer-lasting duration of an erection.

Additional Information

my.webmd.com
Erectile Dysfunction: How an Erection Occurs
www.people.virginia.edu
Normally, sexual stimulation in the male is followed by release of nitric oxide (NO) in the corpus cavernosum of the penis. NO activates the enzyme guanylate cyclase in the smooth muscle cells which allows for the relaxation of the penile arteries and an increase flow of blood into the penile cavity. The effect of Viagra is to allow the accumulation of cGMP by inhibiting the phosphodiesterase action which tends to magnify the effect of NO release.
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