Q. What are some of the side effects of Viagra?
A. Let me first explain how Viagra works; this might help you understand the side effects better.
The mechanism of erection is a complex process that we as physicians are only beginning to understand. We know that when a man is aroused, the nerves to the penis cause the smooth muscle in the penis to relax; as a result, the penis fills with blood. When filling is complete, the penis is rigid. It normally remains that way until ejaculation, when a different set of nerves to the penis is activated, and the smooth muscle contracts, resulting in loss of the erection.
So, to achieve and maintain a good erection, you need cooperation between the nerves and the blood supply to the penis. Many medical conditions, such as diabetes, can damage the nerves or blood supply to the penis. The result is lack of erections (erectile dysfunction). Other conditions, such as atherosclerosis (hardening of the arteries), can cause erectile dysfunction when the arteries to the penis become clogged. In addition, many medications for high blood pressure have erectile dysfunction as a side effect. This means that the most important thing to do before taking Viagra is to see a urologist to find out why you need it.
The drug works like this. Viagra (sildenafil) blocks the action of the enzyme phosphodiesterase, which leads to accumulation of a substance called cyclic guanyle monophosphate (Cgmp). Cgmp acts as messenger in the cells to stimulate them. In the smooth muscle of the penis, the result of this cell stimulation is relaxation and filling of blood. Viagra is called a “type 5 phosphodiesterase inhibitor” because it is supposed to be selective for the enzyme in the penis only. Other forms of the enzyme are present throughout the body, and the drug’s function is different in each of these different parts. Unfortunately, some of those effects involve parts such as the eyes, the salivary glands and the blood vessels.
The most important contraindication to taking Viagra is the use of nitroglycerin medication. Some people take this type of medication for their hearts or blood pressure. The combination of Viagra with nitros is serious, as both drugs can relax the blood vessels, so the combination can cause the blood pressure to drop too low. Other unwanted effects include:
- headache
- flushing
- upset stomach
- stuffy nose
- urinary tract infection
- visual changes, such as mild and temporary changes in blue/green color vision or increased sensitivity to light
- diarrhea
These are only the more common side effects. Other effects have been reported. For a more complete list, see your doctor.