Once upon a time Cocaine used to be up with Heroine in the pantheon of Big Bad Drugs.

We used to think we knew what cocaine meant - it meant a bad, dangerous habit, a short-circuit to pleasure that was indulged in by those on a fast track to ruin. Unless, of course, you indulged in it yourself, in which case you were able to keep your sordid little habit under control and besides, it wasn't sordid, on the venerable principle that an alcoholic is someone you don't like who drinks as much as you. It has, alone among the pharmacopoeia, the property of turning its users into hypocrites.

But the fuss, or rather, the non-fuss, about David Cameron's drug use has changed all that. Although it is perhaps too early to say whether Labour or even the Tories will decide to capitalise on his near-admittance of cocaine use before becoming an MP (and there's a sentence that I could never have imagined writing, even six months ago), it seems at the moment as if he is going to get away with it.

If you're doing it in a toilet, then you will probably feel even more furtive and squalid. Felicitously, the drug is designed to banish, if only temporarily, such feelings. If it didn't, no one would do it any more. These matters used to be handled with a little more dignity. Compare the image of someone crouched over a bog lid with paper currency up their hooter with the one offered us at the beginning of The Sign of the Four: "Sherlock Holmes took his bottle from the corner of the mantelpiece and his hypodermic syringe from its neat morocco case. With his long, white, nervous fingers he adjusted the delicate needle, and rolled back his left shirt-cuff. For some little time his eyes rested thoughtfully upon the sinewy forearm and wrist all dotted and scarred with innumerable puncture-marks. Finally he thrust the sharp point home, pressed down the tiny piston, and sank back into the velvet-lined armchair with a long sigh of satisfaction."

It's bad, and he shouldn't be doing it - but it isn't half glamorous. Just look at the adjectives and adverbs: "neat", "delicate", "thoughtfully", "velvet-lined" - even "long, white, nervous" attests to a very refined, aestheticised excitement. Doyle and Watson may have disapproved of Holmes's cocaine habit, but the disapproval is bound up with a strong, sensual awareness of the excitement that even the thought of the drug can generate. And it is this which we thrill to when we are presented with images of hard drug use. The iconography has a malevolent pull to it - and Doyle was writing at a time when the drug wasn't even illegal.

Which is that someone who is having a line is supplying himself with qualities and emotions that should rather be earned, such as confidence, talkativeness and an attractive self-image. To take a short-cut to these is as much to admit that one lacks them in oneself - and with such widespread experience, whether at first- or second-hand, there is now a pragmatic, realistic attitude to cocaine use rather than one that is stoked by sensational journalism. The news that the overwhelming majority of banknotes now contain traces of the drug gave everyone an opportunity to reflect on the drug's current place in society, whether as metaphor or simple fact. Did anyone, for instance, take any pleasure in the pictures of Boy George's recent arrest for possession in New York - in which he looked anxious, defeated, as unlike the person we remember as Boy George as you can get - or in the fact that he faces a five-year prison sentence in an American jail if convicted? Once upon a time the brouhaha would have been deafening. Now all there is is a quiet sympathy.