Although Viagra has become a virtual synonym for virility, new research shows that the drug may, in fact, reduce a man's fertility. New research from the Queen's University in Belfast suggests that the drug may sort out one problem only to cause a host of others - including infertility.
The drug works by blocking an enzyme called phosphodiesterase-5 (PDE-5). This enzyme normally breaks down the messenger molecules involved in the energy process of cells. Basically, the effect of this is to increase energy levels in the cells, thereby increasing blood flow to the penis while, at the same time, constricting the outflow of blood. Although this will undoubtedly aid potency, it also appears to speed up other sperm activity, including motility (sperm movement) and the timing of a particular chemical reaction that is vital in enabling sperm to penetrate and fertilise an egg.
Speeding up sperm
A process called the 'acrosome reaction' occurs when the head of the sperm releases digestive enzymes to break down the egg's protective outer layer, thus enabling the sperm to enter. Sperm that are spent of these enzymes are said to have 'fully reacted'.
The Queen's University researchers, led by Dr Sheena Lewis, discovered that Viagra accelerates this entire process, causing the acrosome reaction to occur earlier in the sperm's journey. This means that, by the time the sperm reaches the egg, it has exhausted its supply of digestive enzymes.
The researchers obtained 45 samples of sperm and treated half of them with Viagra, using the equivalent concentration of what would be in the blood of a user taking a single 100-mg dose. Within 15 minutes and for the next several hours, the sperm started speeding up. After two hours, nearly 80 per cent of the Viagra-treated samples had fully reacted.
This latest study is particularly worrying because of the change in the type of men now comprising the vast population who use Viagra and other similar drugs. When first made available in 1998, Viagra was aimed at middle-aged men with erectile problems. However, of the 16 million men who have taken it, an increasing percentage are young men who use it simply to enhance their sexual activity. Furthermore, the Queen's team has discovered, through an audit of fertility clinics, that more than 45 per cent of men attending clinics with their partners are using the drug to help produce sperm samples on demand.
Although these are test-tube studies, which may produce different results from those in the body, they do have parallels with the research by Lewis' team on mice. Male mice that were given Viagra and allowed to mate with females produced 40 per cent fewer embryos than those given a placebo. Furthermore, the embryos that were produced were less likely than normal to survive.
Dr Lewis says she is concerned about the effects of such misfiring on human embryos, too. The acrosome reaction causes the channelling of charged calcium ions, which can affect the mechanisms of other cells - including those involved in the early development of an embryo.
The Queen's University team has now started another study of sperm from men taking Viagra. The preliminary evidence based on 17 men shows that the drug indeed has a pronounced effect in speeding-up sperm.
Don't take these drugs
* With heart drugs: nitric-oxide donors (such as amyl nitrite or nitroprusside), nitrate heart medications (such as nitroglycerin), vasodilators or alpha-blockers, all of which can cause a sudden drop in blood pressure
* With opiate pain-relievers like codeine (which can cause priapism), cimetidine, erythromycin, azole antifungals, mibefradil and rifamycin
* If you have a history of heart attack or stroke.