About 550 men around the world were taking Viagra for over 1 year, and about 3700 men of different ages (19-87) were treated with it during its pre-marketing clinical trials.

When men took Viagra as recommended in flexible-dose, some of them reported changes in vision (predominantly color tinge to vision, and sensitivity to light); headache, dizziness, rash, urinary tract infection, dyspepsia, flushing and nasal congestion. Men who exceeded the recommended dose reported the identical side effects more frequently.

Fixed-dose studies showed that the most common side effects at 100 mg doses were abnormal vision and dyspepsia.

Post-Marketing Reports

Many of the patients preexisting cardiovascular risk factors reported the following side effects associated with taking Viagra: hypertension, myocardial infarction, pulmonary hemorrhage, etc. The most severe side effect reported was sudden cardiac death; however it wasn’t possible to conclude whether it was related directly to Viagra.

Among other serious side effects, that might be associated with Viagra, were sudden decrease or loss of hearing, anxiety, amnesia, long-lasting erection, decreased or loss of vision, bleeding, and seizure. Many, but no all, of men who reported these problems had diabetes, hypertension and other risk factors.

Everybody knows how Viagra acts. It leads to male erection when men are sexually aroused. But how is this effect achieved? And why does Viagra work only when a man is sexually aroused? What really makes men get an erection? We will try to answer all these and more questions in this article.

Most articles don’t tell us about penis. But since we are talking about Viagra, we should explain some of the physiological characteristics of male body. We will use the following scheme for brevity:

1 — bladder;
2 — pubic bone;
3 — penis;
4 — corpus cavernosum;
5 — glans;
6 — foreskin;
7 — urethra (urine tube);
8 — colon;
9 — rectum;
10 — seminal vesicle;
11 — ejaculatory duct;
12 — prostate;
13 — glandula Cowperi;
14 — anus;
15 — vas deferens;
16 — epididymis;
17 — testicle;
18 — scrotum

It is not difficult to guess that male genital-urinary system is meant for two functions:
• Urination or the ejection of urine from the bladder.
• Ejaculation or the ejection of sperm and semen.

Viagra helps to perform the second function.

Under normal circumstances ejaculation occurs as a result of a process that can be divided into 3 stages:
• A man gets sexually aroused.
• A man erects in response to penis stimulation.
• Penis stimulation causes ejaculation.

It sounds simple enough. But the second stage does not always occur in real life, and therefore ejaculation does not occur as well. Why does it not happen? We need to get a little deeper into male anatomy and the actual process of erection in order to answer this question.

We usually use our muscles to move any part of our body. It acts the following way: we think about moving, our muscles contract, and the part of our body makes a move. This is not the case with a penis. Blood pressure but not muscles are used in the process of erection.

It is easier to compare erection with the process of pumping air into a balloon. Only cavernous bodies are used instead of the balloon, and blood is used instead of air.

Erection is regulated by arteries and veins. Arteries fill cavernous bodies with blood, and veins pump blood out of them. The arteries are narrowed while erection is absent, and the veins keep working on the blood outflow and not letting it accumulate inside the penis. Once a man gets sexually excited, the arteries open and let the blood fill the cavernous bodies. This leads to an erection.

If the arteries do not open properly, the erection will not occur. This is the main cause of erectile dysfunction (ED). We need to open arteries in order to solve this problem. And we will discuss this issue in the next part of our article.

The first breakthrough in ED treatment occurred in 1983. Before this it was considered that erection dysfunction was caused mainly by mental health problem. Only in 1983 Dr. Giles Brindley proved the possibility of calling an artificial erection by the injection of Phentolamine at the American Urological Association meeting (this was a memorable show because the doctor demonstrated the injection and its results right on the stage).

What did phentolamine do? It relaxed muscles. We need to pay attention to different types of muscles in our body in order to understand how this affected the erection. There are three types of them:
● Skeletal muscles – you can perfectly see them at bodybuilding competitions.
● Cardiac muscles – they make up our heart.
● Smooth muscles – they can be found in blood vessels, stomach and intestine. You cannot control this type of muscles as they usually act spontaneously.
Smooth muscles play a key role in erection, and phentolamine relaxes them. This is what happened at the meeting of urologists in 1983:
● The arteries of a flaccid penis were contracted and they didn’t let the blood fill the cavernous bodies.
● Phentolamine injection relaxed smooth muscles in the arteries walls inside the penis making them open.
● Blood filled the cavernous bodies, and erection occurred under its pressure.

So, erectile dysfunction had been treated with injections of smooth muscle relaxants since the mid 1980’s. And then Viagra was produced and it changed everything. The advantage of pills over injections is obvious. But there was a serious difference in the way they acted. Phentolamine caused an immediate and uncontrollable erection. Viagra causes erection in the case of sexual arousal only.

How does a pill relax smooth muscles in the penis only in the case of sexual arousal and doesn’t relax smooth muscles in entire body? We need to study the circulatory system in order to answer this question.

How is it possible to get an erection with the help of a pill? Phentolamine will not help here because it relaxes all smooth muscles in the body, and this can cause serious problems. It is necessary to produce a medication that will act exclusively on smooth muscles in the penis arteries. Thus we need to learn more about blood flow.

So, as we all know, our heart is like a pump that pumps blood through our body. However different parts of the body require different amounts of blood at different times. For example:
● Your body has to send more blood to your stomach and digestive tract if you are full.
● Your body needs to send more blood to your hand and feet muscles if you are running a marathon. At the same time the delivery of blood to your stomach will be significantly reduced in order to save oxygen for your feet.

In other words, our body needs a set of valves for blood flow regulation in particular parts of the body. And our brain, respectively, should have control over them and be able to open and close these valves when needed. The penis is one of those parts of the body which valve is regulated by human brain. How does it happen? We’ll explain it further.

“Valves” open and close with the help of muscles in the walls of arteries in a human body. When they relax, arteries open and blood flow increases. This happens in response to chemical signals controlled by the brain. This mechanism can be divided into four steps:
1. The brain sends a signal to a particular nerve fiber. This fiber ends with NANC nerve cell in the artery near the point where you want to change the bloodstream. NANC is a non-noradrenergic non-cholinergic transmitter that can produce nitric oxide.
2. NANC injects nitric oxide into blood and the neighbouring cells.
3. Nitric oxide stimulates the enzyme called guanylate cyclase in the neighbouring cells and this enzyme starts to produce a chemical known as cyclic guanosine monophosphate (cGMP).
4. cGMP causes relaxation of smooth muscles in the arteries, and this increases the blood flow.

A phosphodiesterase (PDE) is an enzyme that is used to deactivate cGMP. It breaks up cGMP on its original components. cGMP is produced as long as your brain sends the signal. As soon as it stops sending the signal, the effect will gradually disappear as a result of PDE action.

This is how valves work in our body. But how is it related to an erection?

The lack of cGMP production is a main cause of ED (especially age-related ED). The brain sends a signal. cGMP is produced. But the arteries are not open widely enough. The problem is identified. Now it’s necessary to decide how to create a drug that will act on the penis valve only.

Based on what we have learned so far, we can define three ways of how to increase blood flow in the penis:
1. By increasing the amount of nitric oxide in the penis.
2. By increasing the amount of cGMP produced in the penis in response to nitric oxide.
3. By reducing the amount of PDE in the penis in order to allow cGMP reaching the required amount without being broken up.

Viagra uses the third way. The reasons for this can be found in one interesting PDE feature.

Human body produces at least 11 different types of PDE. And only one of them (PDE5) is mostly found in penis only. Once this fact was discovered, the invention of Viagra was no longer a problem. Pfizer had only to find a chemical that would block PDE5 only. Its affect on the rest of the body would be reduced to a minimum in such case.

PDE5 is an enzyme. And enzyme is a protein folded in a special way and speeding up a chemical reaction. For example, the enzyme of maltase has an ideal shape for a maltose molecule. As soon as the molecule is attached to it, the enzyme splits it into two molecules of glucose:

PDE 5 is the enzyme that attaches itself to cGMP and breaks it apart. Pfizer had to find a substance that would glue to PDE5 and wouldn’t let it do its job. This substance was found. It was sildenafil citrate which is contained in Viagra.

With the intake of Viagra sildenafil citrate passes through our body affecting the enzyme PDE5 only. The drug remains in the blood system for approximately four hours, and then it is derived by liver and kidneys.

So, the complete scheme of Viagra acting is as follows:
● A man takes a pill of Viagra.
● Sildenafil citrate enters his bloodstream and spreads throughout his body.
● Sildenafil citrate joins PDE5 and stops its work.
● The brain sends a regular signal to NANC cells in the penis, when a man is sexually aroused, and these cells produce nitric oxide.
● Nitric oxide creates cGMP that relaxes the arteries in the penis.
● cGMP doesn’t break up because PDE5 is not working. It builds up and allows the arteries to open up.
● Bloods fills the cavernous bodies, and a man gets an erection.
This works in most cases. But side effects are also possible. We will talk about them in the next part of our article.

The main drawback of taking Viagra is having its effect on your face. Your girlfriend can easily guess that you have taken this pill because your face skin reddens, your face is slightly swollen, your nose is stuffed making your breath difficult, and your eyes are red. This destroys the privacy of your treatment because everything is clearly seen on your face. This is very important on your first date when you want to impress your woman. But if your partner is aware of the fact you are taking Viagra you do not have to worry about being red in the face.

Heart

The tense heart is a more severe drawback of taking Viagra. When during a sexual intercourse your rate increases to high rhythms you can feel your heart getting heavier and pounding, etc. This feeling is more powerful if you have drunk alcohol before this. You should be careful with your heart as this might have a sad ending.

Hair

Your hair can weaken and start falling out if you are having a long-term course of Viagra treatment.

Positive Effects

Your subconscious will save the memories of your successful sexual intercourse with Viagra, and as a result you will become more confident in yourself. The result of such psychological therapy can be amazing. It can even help you get a natural erection the next time without taking any pills.

There are several drugs such as Viagra which is very effective in curing conditions such as organic ED. Over 23 million men around the world have benefited from the drug’s use. However the drug is not free of side effects. Retinal vascular disease, intraocular pressure and other eye problems such as blurred sight and high sensitivity to light are the side effects accompanying the drug’s use. Viagra has been approved by the FDA for Erectile Dysfunction (ED). Levitra, manufactured by Bayer Pharmaceuticals and Cialis, manufactured by Eli Lilly are the other 2 drugs approved for the same purpose.

The aforesaid drugs can be used to treat ED. The drugs can be injected or taken as penile suppositories. These drugs work by improving the Nitrous Oxide (NO) efficiency. NO allows for engorgement and erection by dilating the blood vessels within the penis. Oral apomorphine or apomorphine injections are also used to treat this problem. There are also a number of herbal cures to treat the problem of erectile dysfunction. These herbs help in leading to an erection by improving the blood flow to the penis. The most effective herbs that can cure ED are Ginkgo Balboa and Ginseng. The Chinese have used these herbs from time immemorial to improve sexual performance and as general health tonics. Treatments involving surgical methods include penile implants that involve the use of vacuum pumps which can maintain an erection for half an hour. If you suspect a case of ED, it is advisable to visit your doctor immediately as it can also indicate a symptom of some other underlying disease.