Insomniacs know all there is to know about broken promises. Gadget catalogues slide from between the pages of Sunday supplements offering miracle pillows, orthopedic beds, life-changing humidifiers and CD compilations of soporific seashore noises - all lucrative for their manufacturers but not noticeably relieving the agonies of the estimated 10m British adults who suffer from sleeplessness. Just trying to plough through the proliferating and near-identical volumes of self-help literature on the subject ought to induce slumber, but even that's not foolproof. This, after all, is the paradox of sleep: the more energy you focus on eliminating the problem, the harder it becomes to reach a goal you can only reach by forgetting that you want it.

Which is why we should offer a decidedly cautious welcome to the latest "revolution" in sleep treatment. But a welcome nonetheless, because Sonata - the appropriately restful tradename for a new drug launched in the UK later this week by Wyeth-Ayerst Laboratories - really does appear to bring us significantly closer to the "sleep on demand" craved by the nation's tossing and turning hordes.

Traditional sleeping pills - benzodiazepines like Valium - launch an all-out assault on the insomniac's nervous system, guaranteeing a night's sleep but causing collateral damage in the form of next-day grogginess, a nasty reaction with alcohol and, above all, the prospect of dangerous dependency. Sonata, according to its makers and promising pre-launch clinical trials, behaves more like the fabled smart missile, targeting the relevant part of the brain, then breaking down and leaving the body swiftly - doing away with next-day side-effects and, as far as researchers are currently aware, with dependency. Crucially, in consequence, it can be taken in the middle of the night, when sleeplessness strikes, anytime up to four hours before you plan to rise. In the arcane jargon of sleep research, the drug "preserves the natural sleep architecture".

To its credit, Wyeth has resisted the temptation to slap a heartstopping price tag on Sonata: GPs' budgets will only pay £3.60 for every two weeks of treatment prescribed. This is not a display of selfless generosity on the part of a pharmaceuticals firm - that really would be revolutionary - but instead reflects the manufacturer's certainty of reaching an enormous, and enormously profitable, mass market: 50% of Britons suffer disrupted sleep, 24% of them frequently; the company further claims that "around a third of patients consulting their GPs are dissatisfied with their sleep".

It's a surprisingly youthful market, too, given that sleep problems are traditionally associated with older people. GPs are reporting anecdotal evidence of a significant increase in the proportion of insomniac patients under 40. A key prob able reason is the growth of the 24-hour society and the flexible working it demands. Studies have shown that 65% of people who frequently alternate between day and nightshifts suffer from disrupted sleep patterns.

Sonata may well live up to its promise, but it will be breaking the mould if it does. "Just about every other sleep drug introduced onto the market in the last 20 years has claimed to be better than anything else, and to have no side-effects, so one has to be cautious," says Professor Jim Horne of the sleep research centre at Loughborough University, and a maverick in the field. Our troubled relationship with sleeping pills, Horne argues, stems less from a lack of innovations in the lab than from some fundamental misunderstandings about who should use them and how they really work.

"Most insomniacs don't complain of sleepiness during the day, so though they find wakefulness at night upsetting, they don't actually need more sleep than they're getting," he says. "There's a category of insomnia that is associated with feeling worn out all day, but those people don't respond to sleeping tablets anyway." Even when they do work, the medications function not so much by bringing on sleep as by reducing anxiety - in other contexts, benzodiazepines are used as tranquilisers - making the failure to fall asleep seem less distressing.

This is small comfort for the sleepless millions who want rest without addiction, and it's to them that Sonata's aspirin-like convenience and lack of stigma is likely to appeal the most. Ultimately, if they want it to work, it probably will: "Pills don't necessarily mean you get to sleep sooner," says Horne. "Time just feels like it's passing less slowly, so you worry about it less. And then you sleep."