How Viagra work?

Erectile dysfunction (ED) or impotence is a sexual dysfunction characterized by the inability to develop or maintain an erection of the penis for satisfactory sexual intercourse regardless of the capability of ejaculation. There are various underlying causes, such as diabetes, many of which are medically reversible.

How Viagra work?

The causes of erectile dysfunction may be physiological or psychological. Psychological impotence can often be helped by almost anything that the patient believes in; there is a very strong placebo effect.

Due to its embarrassing nature and the shame felt by sufferers, the subject was taboo for a long time, and is the subject of many urban legends. Folk remedies have long been advocated, with some being advertised widely since the 1930s. The introduction of perhaps the first pharmacologically effective remedy for impotence, sildenafil (trade name Viagra), in the 1990s caused a wave of public attention, propelled in part by the news-worthiness of stories about it and heavy advertising.

The Latin term impotentia coeundi describes simple inability to insert the penis into the vagina. It is now mostly replaced by more precise terms.

Medical symptoms

Erectile dysfunction is characterized by the inability to maintain an erection. Normal erections during sleep and in the early morning suggest a psychogenic cause, while loss of these erections may signify underlying disease, often cardiovascular in origin. Other factors leading to erectile dysfunction are diabetes mellitus (causing neuropathy) or hypogonadism (decreased testosterone levels due to disease affecting the testicles or the pituitary gland).

Medical diagnosis

There are no formal tests to diagnose erectile dysfunction. Some blood tests are generally done to exclude underlying disease, such as diabetes, hypogonadism and prolactinoma. Impotence is also related to generally poor physical health, poor dietary habits, obesity, and most specifically cardiovascular disease such as coronary artery disease and peripheral vascular disease.

A useful and simple way to distinguish between physiological and psychological impotence is to determine whether the patient ever has an erection. If never, the problem is likely to be physiological; if sometimes (however rarely), it is more likely to be psychological. The current diagnostic and statistical manual of mental diseases (DSM-IV) has included a listing for impotence.

A wide variety of options exist for treating erectile dysfunction. They include everything from medications and simple mechanical devices to surgery and psychological counseling. The cause and severity of your condition are important factors in determining the best treatment or combination of treatments for you. You and your doctor may also want to consider how much money you’re willing to spend and the personal preferences of you and your partner. If erectile dysfunction is the result of a medical condition, the cost of treatment may be covered by insurance.

Uncontroversial treatments

PDE5 Inhibitors
The prescription PDE5 inhibitors sildenafil (Viagra), vardenafil (Levitra) and tadalafil (Cialis) are prescription drugs which are taken orally. They work by blocking the action of PDE5, which causes cGMP to degrade. cGMP causes the smooth muscle of the arteries in the penis to relax, allowing the corpus cavernosum to fill with blood.
* Sildenafil (Viagra)
* Tadalafil (Cialis)
* Vardenafil (Levitra)

The Food and Drug Administration (FDA) approved Viagra in 1998, and it became the first oral medication for erectile dysfunction on the market. Since then, doctors have written millions of prescriptions for the blue, diamond-shaped tablets. But Viagra is no longer the only pill that treats this condition. Levitra and Cialis are two other options.

Viagra, Levitra and Cialis work in much the same way. Chemically known as phosphodiesterase inhibitors, these drugs enhance the effects of nitric oxide, a chemical messenger that relaxes smooth muscles in the penis. This increases the amount of blood and allows a natural sequence to occur — an erection in response to sexual stimulation. These medications don’t automatically produce an erection. Instead they allow an erection to occur after physical and psychological stimulation. Many men experience improvement in erectile function after taking these medications regardless of the cause of their impotence.

These medications share many similarities, but they have differences as well. They vary in dosage, duration of effectiveness and possible side effects. Other distinctions — for example, which drug is best for certain types of men — aren’t yet known. No study has directly compared these three medications.

Although these medications can help many people, not all men can or should take them to treat erectile dysfunction. If you’ve had a heart attack, stroke or life-threatening heart rhythm during the last six months, don’t take these medications. If you’ve been told that sexual activity could trigger a cardiac event, discuss other options with your doctor. In addition, don’t take Viagra, Levitra or Cialis with nitrate medications, such as the heart drug nitroglycerin. The combination of these medications, which work to widen (dilate) blood vessels, can cause dizziness, low blood pressure, and circulation and heart problems.

Don’t expect these medications to fix your impotence immediately, because that’s not always the case. Dosages may need adjusting. Or you may need to alter when you take the medication. Before taking any medication, make sure to discuss with your doctor its potential benefits and side effects.

Vacuum pump
An external vacuum pump will produce an engorged penis with success approaching 90%; a penis ring will maintain this state, although it should be removed after not more than 30 minutes. The erection is not as rigid or hard as a natural erection; drugs or injections, when they work, may be preferable. Various studies show the degree of satisfaction of users and their partners to be vary variable, even when drugs and injections do not work; in one study, about 20% of men who tried a (high-priced) pump decided to proceed to purchase one. Other studies show higher percentages of satisfied users.
In some cases frequent use of a vacuum pump can eventually improve the degree of erection attainable without use of the pump. Claims of cheap “penis pumps” to permanently increase maximum penis size should be viewed with caution, however.
Some vacuum pumps, such as Osbon ErecAid, are sold at a higher price with 100% refund within 90 days to dissatisfied users, with a somewhat lower price with 50% refund guarantee. This pump is supported by medical insurance schemes, including the UK’s NHS and US Medicare and private insurers. The better-known pumps sell for prices of around 200 GBP/400 USD (2006). There is at least one vacuum pump with rings which sells for around one-fifth of this price.

(Specific devices are mentioned for information only; mention should not be taken as endorsement).

Inflatable implant

Rigid implant

Surgical treatment of certain cases

Controversial and unapproved treatments

Bremelanotide
The experimental drug Bremelanotide (formerly PT-141) does not act on the vascular system like the former compounds but allegedly increases sexual desire and drive in males as well as females. It is applied as a nasal spray. Bremelanotide allegedly works by activating melanocortin receptors in the brain. It is currently in Phase IIb trials.

hMaxi-K
hMaxi-K is a form of gene therapy using a plasmid vector that expresses the hSlo gene, that encodes the alpha-subunit of the Maxi-K channel. It has undergone phase I safety trials.

Ginseng
A double-blind study appears to show evidence that ginseng is better than placebo: see the ginseng article for more details.

Enzyte
Enzyte is a product that has been advertised by saturation coverage on television channels such as CourtTV. However, the Center for Science in the Public Interest (CSPI) has filed a complaint with the Federal Trade Commission (FTC) about Enzyte for deceptive advertising. It is manufactured by Berkeley Nutritionals, which is alleged to be the subject of an investigation by the Attorney General of Ohio and the defendant in class-action lawsuits.

Enzyte is a supplement that claims to increase the male libido or frequency of erections of the penis. Commercials for Enzyte are shown regularly on television. These commercials feature a man named Bob who never stops smiling, apparently because he had taken Enzyte and improved the size of his sex organs. The commercials are riddled with symbolic phallic imagery, e.g. golf clubs, remarkably tall glasses of iced tea, and a hose spraying barely a trickle of water (carried by someone who doesn’t use Enzyte).

The effectiveness of Enzyte is in dispute. Some medical professionals in fact advise against taking Enzyte, saying that it can lead to damage. The Center for Science in the Public Interest have urged the Federal Trade Commission to disallow further television advertising for Enzyte due to a lack of proper studies supporting claims. Enzyte maker Berkeley Premium Nutraceuticals, Inc., is currently under a class action lawsuit for false advertising.

Enzyte is said to contain: Tribulus terrestris; Yohimbe Extract; Niacin; Epimedium; Avena sativa; Zinc Oxide; Maca; Muira Pauma; Ginkgo biloba; L-Arginine; Saw Palmetto. Other ingredients: gelatin, rice bran, oat fiber, magnesium stearate, silicon dioxide.

Herbal and other alternative treatments
These are generally ineffective when tested blind, but may be useful for their psychological (placebo) effect: if a good result is expected, any highly-praised, and often expensive, treatment can be effective. Reputable drugs can also benefit from the same effect.

Prelox
Prelox is a Proprietary mix/combination of naturally occurring ingredients, L-arginine aspartate and Pycnogenol. In double blind tests carried out by Dr. Steven Lamm at New York University School of Medicine, 81.1% of men overall judged Prelox to be effective in improving their ability to engage in sexual activity. Prelox for improvement of erectile function: A review European Bulletin of Drug Research, Volume 11, No. 3, 2003. Steven Lamm, Frank Schoenlau, Peter Rohdewald Whilst the supplements should be taken daily, the manufacturers claim that it brings the spontaneity back into ones’ love life; unlike other products which must be remembered to be taken a fixed time before sexual activity.

Non-surgical ED Treatment Treatment Sex Therapy

A significant number of men develop impotence from psychological causes that can be overcome. When a physiological cause is treated, subsequent self-esteem problems may continue to impair normal function and performance. Qualified therapists (e.g., sex counselors, psychotherapists) work with couples to reduce tension, improve sexual communication, and create realistic expectations for sex, all of which can improve erectile function. Psychological therapy may be effective in conjunction with medical or surgical treatment. Sex therapists emphasize the need for men and their partners to be motivated and willing to adapt to psychological and behavioral modifications, including those that result from medical or surgical treatment.

Medical Treatment Oral Medication Oral medications used to treat erectile dysfunction include selective enzyme inhibitors (e.g., sildenafil Viagra, vardenafil HCl Levitra, tadalafil Cialis) and yohimbine (Yohimbine, Yocon).

Selective enzyme inhibitors are available by prescription and may be taken up to once a day to treat ED. They improve partial erections by inhibiting the enzyme that facilitates their reduction and increase levels of cyclic guanosine monophosphate (cGMP, a chemical factor in metabolism), which causes the smooth muscles of the penis to relax, enabling blood to flow into the corpora cavernosa. Patients taking nitrate drugs (used to treat chest pain) and those taking alpha-blockers (used to treat high blood pressure and benign prostatic hyperplasia) should not take selective enzyme inhibitors.

Men who have had a heart attack or stroke within the past 6 months and those with certain medical conditions (e.g., uncontrolled high blood pressure, severe low blood pressure or liver disease, unstable angina) that make sexual activity inadvisable should not take Cialis. Dosages of the drug should be limited in patients with kidney or liver disorders.

Viagra is absorbed and processed rapidly by the body and is usually taken 30 minutes to 1 hour before intercourse. Results vary depending on the cause of erectile dysfunction, but studies have shown that Viagra is effective in 75% of cases. It helps men with erectile dysfunction associated with diabetes mellitus (57%), spinal cord injuries (83%), and radical prostatectomy (43%).

In clinical studies, Levitra has been shown to work quickly, provide consistent results, and improve sexual function in most men the first time they take the drug. It also has shown to be effective in men of all ages, in patients with diabetes mellitus, and in men who have undergone radical prostatectomy.

Cialis has been shown in clinical trials to stay in the body longer than the other selective enzyme inhibitors. It promotes erection within 30 minutes and enhances the ability to achieve erection for up to 36 hours.

Common side effects of selective enzyme inhibitors include headache, reddening of the face and neck (flushing), indigestion, and nasal congestion. Cialis® may cause muscle aches and back pain, which usually resolve on their own within 48 hours. Yohimbine improves erections for a small percentage of men. It stimulates the parasympathetic nervous system, which is linked to erection, and may increase libido. It is necessary to take the medication for 6 to 8 weeks before determining whether it will work or not. Yohimbine has a stimulatory effect and side effects include elevated heart rate and blood pressure, mild dizziness, nervousness, and irritability. Yohimbine’s effects have not been studied thoroughly, but some studies suggest that 10% to 20% of men respond to treatment with the drug.

Ease of administration makes oral medication advantageous. Some drugs, however, are suitable for only a relatively small group of men, and in many cases, oral medications may by less effective than other treatments.

Self-Injection Self-injection involves using a short needle to inject medication through the side of the penis directly into the corpus cavernosum, which produces an erection that lasts from 30 minutes to several hours. Prostaglandin (alprostadil, Caverject, Edex), and phentolamine (Regitine) produce results similar to Viagra but are localized in the penis after injection. They cause vascular dilation and a relaxation of smooth muscle. Prostaglandin is the only substance currently approved for erectile dysfunction treatment. Phentolamine is a heart medication with similar effects used by some physicians to treat impotence. These drugs have been shown to produce erections in 80% of men who inject them. Some men claim that they produce erections that feel natural and improve sex. The injections are relatively painless and create an erection that begins about 5 to 15 minutes after the injection. It is recommended that self-injection be performed no more than once every 4 to 7 days. Side effects include infection, bleeding, and bruising at the injection site, dizziness, heart palpitations, and flushing. There is a small risk for priapism (an erection that lasts for more than 6 hours and requires medical relief). Repeated injection may cause scarring of erectile tissue, which can further impair erection.

Urethral suppositories containing prostaglandin (aprostadil), like Muse® (Medicated Urethral System for Erections), may be an alternative to injection. Using a hand-held delivery device, a man inserts a prostaglandin pellet through the meatus (penis opening) into the urethra. Prostaglandin is absorbed through the urethral mucosa and into the surrounding erectile tissue. It is available with a prescription, is well tolerated, and may improve erections in 60% of men who use it.

In addition to the side effects associated with injecting aprostadil, pain in the penis and perineum (area between scrotum and rectum) may occur with suppository use. Vacuum Devices Vacuum devices work by manually creating an erection. The penis is inserted into a plastic tube, which is pressed against the body to form a seal. A hand pump attached to the tube is used to create a vacuum that draws blood into the penis, causing the penis to become engorged. After 1 to 3 minutes in the vacuum, an adequate erection is created. The penis is removed from the tube and a soft rubber O-ring is placed around the base of the penis to trap blood and maintain the erection until removed. The ring can be left in place for 25 to 30 minutes.

Vacuum devices work best in men who are able to achieve partial erections on their own. They are easy to use at home, require no other procedure, and typically improve erections regardless of the cause of impotence. Some men experience a numbing feeling after placing the O-ring. Since the penis is flaccid between the ring and the body, the erection may be somewhat floppy.

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