NO is produced by the enzyme NO synthase (NOS).  NOS plays many roles, ranging from homeostasis to immune system regulation. To date, 3 subtypes have been identified: nNOS, iNOS, and eNOS, which are produced by the genes NOS1, NOS2, and NOS3, respectively. This nomenclature is derived from the sources of the original isolates: neuronal tissue (nNOS), immunoactivated macrophage cell lines (iNOS), and vascular endothelium (eNOS). The subtypes are not, however, limited to the tissues from which they were first isolated.
Currently, there are no therapies that cure erectile dysfunction. However, a number of effective therapies are available that allow an individual to have an erection when desired. Depending on the cause of the erectile dysfunction, certain therapies may be more effective than others. Although there is limited data on lifestyle modification, intuitively, decreasing risk factors for erectile dysfunction may help prevent progression of disease.
There are many alternative impotence treatments available but many of them are neither licensed nor legitimate, Beware of sellers offering “herbal” impotence treatments - these remedies do not work and are often sold illegally. You should also be wary of online sellers who offer Viagra and other prescription drugs without asking you for a prescription. Illegal pharmacies often sell counterfeit or fake medication and buying from them could put your health at risk.
Medications: Many common medicines produce erectile dysfunction as a side effect. Medicines that can cause erectile dysfunction include many used to treat high blood pressure, antihistamines, antidepressants, tranquilizers, and appetite suppressants. Examples of common medicines that can cause erectile dysfunction include propranolol (Inderal) or other beta-blockers, hydrochlorothiazide, digoxin (Lanoxin), amitriptyline (Elavil), famotidine (Pepcid), cimetidine (Tagamet), metoclopramide (Reglan), naproxen, indomethacin (Indocin), lithium (Eskalith, Lithobid), verapamil (Calan, Verelan, Isoptin), phenytoin (Dilantin), gemfibrozil (Lopid), amphetamine/dextroamphetamine (Adderall), and phentermine. Prostate cancer medications that lower testosterone levels such as leuprolide (Lupron) may affect erectile function. Some chemotherapies such as cyclophosphamide (Cytoxan) may affect erectile function.
Geographic, Racial, Ethnic, Socioeconomic, and Cultural Variation in Erectile Dysfunction. Very little is known about variations in prevalence of erectile dysfunction across geographic, racial, ethnic, socioeconomic, and cultural groups. Anecdotal evidence points to the existence of racial, ethnic, and other cultural diversity in the perceptions and expectation levels for satisfactory sexual functioning. These differences would be expected to be reflected in these groups' reaction to erectile dysfunction, although few data on this issue appear to exist.
I think that a very powerful argument to young men who want to perform at the highest level is to point out the destructive nature of what they’re doing. If they’re having 18 drinks per week, if they’re having three, four, five drinks at any one time, they’re going to guarantee that their erections are not going to be at the highest level. I can’t tell you the number of men who come in saying, they went out, they had a date, they had a big dinner– which, by the way, is also not a great thing for erections, because all the blood is now going to your gut instead of to the genital area. And how important lifestyle changes are to improving your performance, as well, if not better, than the medications. So make certain that you exercise modestly, not excessively. Make certain that you have a smaller meal on an evening or a day that you want to have a sexual encounter, because you want the blood to go, once again, to the penile area and not to your gut. And really, the whole idea of stress– if you’re stressed out, if you’re worried about a lot of things, if you’re distracted, you can’t initiate that psychic stimulus to your spinal cord and then ultimately to your penis. So stress management is incredibly important.
Conditions associated with reduced nerve and endothelium function (eg, aging, hypertension, smoking, hypercholesterolemia, and diabetes) alter the balance between contraction and relaxation factors (see Pathophysiology). These conditions cause circulatory and structural changes in penile tissues, resulting in arterial insufficiency and defective smooth muscle relaxation. In some patients, sexual dysfunction may be the presenting symptom of these disorders.
None of the ED drugs is safe to take with cardiac drugs called nitrates because it could cause a dangerous drop in blood pressure. Drugs that many men take for urinary symptoms, called alpha blockers, can also lower blood pressure, so take them at least four hours apart from ED drugs. Your doctor may start you on a smaller dose of the ED drug if you already take an alpha blocker, or may recommend the alpha blocker tamsulosin (Flomax), which affects blood pressure less.
Picture the scene. You get home from the bar with your date. You both decided to leave a little early, after only two drinks, because the chemistry was really there and both of you wanted to cut to the chase and get intimate. To discover each other's bodies. To eat of the fruits of passion. In short, to have sex. You stick the key in the lock, swing the door open, and invite her into your beautiful place. OK, well it might not be exactly beautiful. It might be a bit of a mess, frankly. But you don't let that ruin the moment. You turn around and passionately kiss her. How the two of you make it to your bedroom with some clothing still on is anybody's guess. You jump on the bed and hurriedly strip. God — can't this go any faster, you wonder?
Conditions that may be associated with ED include diabetes, [25, 26, 27] hypertension,  , and CAD, as well as neurologic disorders, endocrinopathies, benign prostatic hyperplasia,  , sleep apnea  , COPD,  and depression (see Table 1 below). [32, 33, 34, 35] In fact, almost any disease may affect erectile function by altering the nervous, vascular, or hormonal systems. Various diseases may produce changes in the smooth muscle tissue of the corpora cavernosa or influence the patient’s psychological mood and behavior.
Relationship problems can make it difficult for you to get or stay hard when you’re attempting to have sex with the person you’re in a relationship with. However, if you have this problem and you’re in a relationship that doesn’t mean your relationship is necessarily the reason. There are lots of other reasons you might not be able to get or stay hard (see above).
In prescribing sildenafil, a doctor considers the age, general health status, and other medication(s) the patient is taking. The usual starting dose for most men is 50 mg, however, the doctor may increase or decrease the dose depending on side effects and effectiveness. The maximum recommended dose is 100 mg every 24 hours. However, many men will need 100 mg of sildenafil for optimal effectiveness, and some doctors are recommending 100 mg as the starting dose.
Diabetes mellitus: Erectile dysfunction tends to develop 10 to 15 years earlier in diabetic men than among nondiabetic men. The increased risk of erectile dysfunction among men with diabetes mellitus may be due to the earlier onset and greater severity of atherosclerosis (hardening of the arteries) that narrows the arteries and thereby reduces the delivery of blood to the penis. Atherosclerosis can affect the arteries in the penis, as well as the arteries in the pelvis that supply the penile arteries. Diabetes mellitus also causes erectile dysfunction by damaging nerves that go to the penis, much like the effect of diabetes on nerves in other areas of the body (diabetic neuropathy). Diabetes can also affect the muscles in the penis, leading to troubles with erections. Smoking cigarettes, obesity, poor control of blood glucose levels, and having diabetes mellitus for a long time further increase the risk of erectile dysfunction in people with diabetes.
However, a review of a United Kingdom medical record database found no evidence that the use of 5-alpha reductase inhibitors independently increase the risk for ED. In 71,849 men with benign prostatic hyperplasia (BPH), the risk of ED was not increased with the use of finasteride or dutasteride only (odds ratio [OR] 0.94), or a 5-alpha reductase inhibitor plus an alpha blocker (OR 0.92) compared with an alpha blocker only. In addition, the risk of ED was not increase in 12 346 men prescribed finasteride 1 mg for alopecia, compared with unexposed men with alopecia (OR 0.95). The risk of ED did increase with longer duration of BPH, regardless of drug exposure. 
If a man's arteries become blocked with cholesterol – as a result of genetics, and/or lifestyle factors such as smoking, a poor diet and lack of exercise – it will affect the vessels all over his body. The arteries supplying the penis are relatively small, just 1-2mm wide, and so they become blocked more quickly than others. The blood flow to the area is reduced, meaning erections become more difficult.
However, men are affected psychologically when it comes to achieving erections. For instance, if a man is with a woman for the first time, or even before he feels comfortable with her, he may suffer from performance anxiety. In such a situation, his mind and body are both saying yes, but then they become out of sync. The body is then saying yes, but the mind is filled with question. “Will I be able to perform?” “How long will I last?” “Am I big enough to satisfy her?” “Is she looking at that mole on my stomach?” All kinds of questions may be going through a man’s mind upon getting in bed, and these can be distracting, they can lead to self-doubt, and therefore, failure to achieve or maintain an erection.
My fiancé and I have been together for four years, and while we've had our ups and downs, we're in a good place now and looking forward to our life together. Throughout our relationship, we've made some bad financial decisions. Since I'm the one with the credit cards (his credit is awful), I'm the one that's more affected. We're trying to dig ourselves out of this hole, and he does pay a good portion of the bills, but I recently found out he didn't pay even close to the amount he could have. Meanwhile, I'm basically spending my full paycheck trying to pay off my debts. When I asked about it, he said he didn't just want to "throw all of his money toward it," but that's exactly what I'm doing. Am I wrong to ask him to contribute more? He doesn't spend frivolously or anything, but I feel that we should focus on outstanding balances before trying to save money.
Name of DrugWhen to TakeDoseDietary RestrictionsViagraTake between 30 and 60 minutes (and up to 4 hours) before sex; works for about 4 hoursRecommended dose for most men is 50mgs; after that, dosage may go to as high as 100mg, or as low as 25mg, which may be prescribed for men over 65.Quickly absorbed by the body, less effective after a high-fat meal, and best taken on an empty stomach.Name of DrugWhen to TakeDoseDietary RestrictionsLevitraTake 1 hour before sex; works for 4 to 5 hours, and may be slightly more effective than ViagraStarting dose for most men is 10mgs a day, but men over 65 often start on the 5mg pill.Can be taken with or without food, although slightly less effective after a high-fat meal. Avoid anything containing grapefruit juice; it may make side effects worse.Name of DrugWhen to TakeDoseDietary RestrictionsCialisComes in two forms. The daily pill stays effective in between doses, but may take 4 to 5 days before it begins working. The “weekender” version of Cialis can start working in as little as 30 minutes for men who take the highest dose of the drug (20mgs); it stays effective in the body for up for 36 hours.Daily pill comes in both a 2.5mg and 5mg tablet; most men start with the lower dose. The use-as-needed, “weekender” pill comes in 5, 10 and 20mg strengths; recommended starting dose is 10mg,Can be taken with or without food. Avoid heavy drinking (5 glasses of wine or 5 shots of whiskey); when combined with Cialis, it can lead to headaches, dizziness, an increase in heart rate, and a drop in blood pressure.Name of DrugWhen to TakeDoseDietary RestrictionsStaxyn Take 1 hour before sex, although many men report erections in 20 to 30 minutes. Because Staxyn comes in a sleek black package and is taken as a rapidly dissolving tablet (without water), some men think of it as a more discrete way to treat ED.Comes in 10mg tablets; do not take more than 1 a day.Avoid taking it with any kind of liquid. Should be placed directly on the tongue and allowed to dissolve without chewing.Name of DrugWhen to TakeDoseDietary RestrictionsStendraPrescribing information now recommends taking it 30 minutes before sex. Some men, however, report results in as little as 10 to 12 minutes, depending on the dose. Because of these findings, Auxilium Pharmaceuticals, the Chesterbrook, Pa., company that has U.S. marketing rights to the drug, has asked the FDA to revise the prescribing information.Starting dose is 100mgs for most men, but the 50mg tablet is recommended for men taking alpha-blocker drugs, like those used for high blood pressure and prostate problems.May be taken with or without food, and with a moderate amount of alcohol (3 drinks). Drinking more than that can increase the chances of side effects like rapid heart rate, low blood pressure, dizziness and headaches.Name of DrugWhen to TakeDoseDietary RestrictionsPenile injections & the MUSE suppositoryTake 5 to 10 minutes before planning to have sex; erections last for 30 to 60 minutes.MUSE comes in 4 dosage strengths; most men start at 125mgs. Avoid taking more than twice within a 24-hour period.N/A
In their extensive review, Bassil and coworkers summarise the benefits and risks, with benefits such as improvement of sexual function, bone density, muscle strength, cognition and overall improvement in quality of life. Among the risks that have been suggested include erythrocytosis, liver toxicity, worsening of sleep apnoea and cardiac function, possibly increasing symptoms of benign prostatic hyperplasia (BPH). They also note that although a possibility of stimulation of prostate cancer has been hypothesised, no scientific or clinical evidence exists to this possible risk.38
Think of erectile dysfunction as your body’s “check engine light.” The blood vessels in the penis are smaller than other parts of the body, so underlying conditions like blocked arteries, heart disease, or high blood pressure usually show up as ED before something more serious like a heart attack or stroke. ED is your body’s way of saying, “Something is wrong.” And the list of things that cause erectile dysfunction can include: