Quite a few men believe that a steady intake of alcohol heightens po­tency – but this couldn’t be further from the truth. Chronic excessive alcohol consumption can lead to all kinds of sexual problems. Alcohol attacks the body in various ways: in the long run both the central and the peripheral nervous system can be affected. The substance also has a toxic effect on the testicles. Besides that less testosterone is produced and the liver is progressively less able to break down oestrogen (men also produce a small amount of this female hormone).

In the nineteenth century the effect of various kinds of wine was a serious object of study. The German physician V. G. Vecki believed that the heavier dark-red wines like Bordeaux, Dalmatian and Californian wines and some Spanish varieties have a positive effect on potency.

Champagne was in his view pernicious, increasing the libido but harm­ing the erectile apparatus.

The porter’s famous description of the effects of alcohol in Macbeth still rings true: ‘It provokes the desire, but it takes away the perform­ance.’ Shakespeare’s point is still valid: excessive drinking is bad for the erection mechanism. It is sometimes said of impotence that it is a matter of wanting but not being able. In the case of excessive alcohol consumption, however, the reverse usually applies: one is able, but doesn’t want to.

Nicotine reduces potency through its vascular constrictive effect, meaning simply that the blood supply to the penis is reduced. Research with dogs, which were required to inhale a fixed quantity of nicotine, proved this beyond question. The effect of recreational drugs depends partly on the way in which they are used (smoking, snorting or intravenous injection) and the level of the dose. In addition, it is not exceptional for several drugs to be used simultaneously. Marijuana, methadone and heroin not only lower the testosterone level in the blood, but also result in a raised prolactin level. An excess of that hormone (which triggers milk production in nursing mothers) reduces the desire for sex.

Too high a prolactin level in the blood is fortunately only very rarely the result of a prolactinoma, a tumour affecting the hypophysis. Depending on its size it must be treated by medication, radiotherapy or operation.