It seems scarcely credible today that Sherlock Holmes’s principal private vice was that he was an intravenous drug user, sometimes of morphine, more often – as on this occasion from the opening passage of The Sign Of Four – of cocaine. The vice is not quite so private that Holmes can’t practise it before the concerned gaze of his associate Dr Watson, whose medical training puts him in fear of the physical consequences of Holmes’s habit.

Holmes justifies his recourse to recreational drugs to Watson in these words: “I find it… so transcendently stimulating and clarifying to the mind that its secondary action [i.e. whatever damage it might be doing him] is a matter of small moment… I abhor the dull routine of existence. I crave for mental exaltation.”

These were not uncommon sentiments in the late 19th century, an era when laws to prohibit the use of drugs of all sorts had not yet been formulated. There had long been an association of the use of opium (both smoked and, in the form of laudanum, drunk) with the creative imagination. Experimentation with it was prevalent among the Romantic poets such as Samuel Taylor Coleridge and Percy Bysshe Shelley. But cocaine was something different again.

Coca and Coca-Cola

Prior to 1860, the active ingredient in cocaine was only available in the form of natural coca leaves. The form in which the drug is chiefly used today occurred when the alkaloid present in coca – named cocaine by its discoverer, Dr Albert Niemann – was first isolated. It was then taken up medicinally, and used in herbal tonics such as Vin Mariani, a restorative wine drink that contained cocaine, extracted from the coca leaves by the action of alcohol. For the first few years of its commercial life, coca was also one of the ingredients of Coca-Cola (albeit in tiny concentrations), as its name indicates.

Although cocaine use was prohibited by legislation brought in during the first world war, the link between the coca plant and health took a while to break. As late as 1938, the French cookery bible, Larousse Gastronomique, contained a recipe for "Cocaine Pudding", a variation on zabaglione in which the traditional egg-sugar-and-wine mixture was boosted with extracts of cola and coca steeped in orange syrup. "Not only a very tasty dessert," commented the book, "but also an excellent medicine."

Drugs and writing

Other 19th-century writers to come under the influence of recreational drugs included Robert Louis Stevenson, who wrote The Strange Case Of Dr Jekyll and Mr Hyde (1886) during a non-stop, six-day cocaine binge; Thomas de Quincey, whose 1821 work Confessions Of An English Opium-Eater documents the author’s descent into laudanum addiction, and is the model for many of the drug confessional narratives that have been written since; and, of course, the scandal-courting Lord Byron, who took absolutely anything he came across.

Many commentators have insisted that Alice’s Adventures In Wonderland is suggestively laced with drug references. They point to the chapter "Advice from a Caterpillar", in which Alice has a conversation with a distinctly stoned-sounding caterpillar smoking something unspecified in a hookah pipe, before she is invited to nibble on a giant mushroom, which has the effect of altering her height and, with it, her perceptions of the world around her.