The penis is composed of three cylinders: two on the top, the corpora cavernosa and one on the bottom, the corpus spongiosum. All of these are involved in the process of an erection. The corpora cavernosa are composed of potential spaces that can distend with blood, causing rigidity of the penile shaft. The corpus spongiosum is important for rigidity of the glans of the penis. When aroused, stimulated chemicals are released from the nervous system (nitric oxide is one) that stimulate the arteries to the penis to relax and increase blood flow into the penis. These potential spaces, like a sponge, can expand when more blood flow comes in the penis. Each corpora cavernosa is surrounded by an outer coating the tunica albuginea. When the penis fills with blood, these potential spaces, the sinusoids, compress the veins in the corpora against the side of the tunica albuginea, thus preventing blood from leaving the penis. It is this compression of the veins that allows for the erection to become fully rigid.
Side effects of sildenafil are similar to those from taking niacin or any vasodilator, namely, headaches, lightheadedness, dizziness, and flushing. Some individuals experience a bluish tinge of their cornea, which makes them feel as if they are wearing light blue–tinted sunglasses. This effect can last for several hours. Syncope and myocardial infarction, the most serious side effects, are seen in men who are also taking nitrates for coronary heart disease. Sildenafil also has adverse effects in people with hypertrophic cardiomyopathy because a decrease in preload and after load in the cardiac output can increase the outflow obstruction, culminating in an unstable hemodynamic state.
It’s important to make mention that ED can be associated with stress, hormones, emotional well-being, the nervous system, muscle tone, circulation, medications, and more. While there may be a simple explanation for the inability to maintain an erection, sexual arousal is a complex function of the body, so it’s in your best interest to consult with your doctor if you’re regularly having trouble sustaining an erection and having pleasurable sex.
There is no evidence that mild or even moderate alcohol consumption is bad for erectile function, says Ira Sharlip, MD, a urology professor at the University of California San Francisco School of Medicine. But chronic heavy drinking can cause liver damage, nerve damage, and other conditions -- such as interfering with the normal balance of male sex hormone levels -- that can lead to ED.
There are a number of reasons a man may not achieve the desired result from an oral erectile dysfunction drug. In some cases, a man may experience drug side effects severe enough to outweigh any potential benefit of taking the drug. Possible side effects of these drugs include headache, facial flushing, nasal congestion, and transient abnormal vision. (In October 2007, the FDA added a warning about sudden hearing loss to the package labels of oral erectile dysfunction drugs. While it’s not absolutely clear that the drugs can cause sudden hearing loss, a number of cases have been reported in men within hours or days of taking one of the drugs.)
It's also important to remember that your mental health plays as much a part of your sexual ability as your physical health. Stress and other mental health concerns can cause or make erectile dysfunction worse. Minor health problems may slow your sexual response, but the accompanying anxiety that comes with the slow sexual response can shut things down entirely.