From the Telegraph (UK):

In a cluttered living room in south London, Lee Hogan, a sound engineer and part-time disc jockey, perches on the edge of a cheap leather armchair and bends his head towards a glass water pipe. A friend, kneeling on the floor, holds the stem of the pipe and uses a cigarette lighter to burn a tea-smelling herb. The herb glows red, and as it does so, Hogan places his mouth over the aperture of the pipe (better known as a 'bong' to those in the know). He breathes in deeply, taking a lung-full of smoke.

It's the way that many people choose to inhale marijuana, but this weed is far more potent and far more harmful. Hogan is smoking salvia divinorum, a species of sage that also happens to be the most powerful hallucinogenic herb known to man. It's also perfectly legal.

It doesn't take long for the effects to take hold. Seconds after breathing in the smoke, Hogan leans back in his chair and lets out a deep, slightly manic laugh. He hugs himself and starts to giggle. The giggle then transforms into a whimper, which, in turn, becomes a series of high-pitched squeaks. He is trying to talk, but makes no sense whatsoever. Then, mouth hanging wide open, he looks around the room. His eyes have glazed over and he doesn't seem to know where he is. As he slowly manoeuvres himself in his chair, his head rocking from side to side, he looks like a man who has just been hit over the skull by an iron bar.

Watching young people out of their minds on salvia is the latest YouTube sensation and is fuelling the popularity of the herb. But, for those with a clear head, the films – some of which have been viewed more than a million times – are deeply disturbing. Users are reduced to mumbling wrecks, giggling and screaming, gasping and muttering, waving their hands around as they sink into a sofa or crumple to the floor. What we don't see are the visions, lights, swirls and hallucinations that many say they have experienced. Or the nightmarish sense that they are close to death, going insane or under attack. Titles such as Horrible Salvia Trip speak for themselves. 'What we are witnessing is no less than the world's first internet-driven drugs explosion,' says Dr John Mendelson, a San Francisco-based clinical pharmacologist who is conducting medical trials into how the drug works on the brain.

Salvia, a genus of the mint family, is commonly referred to as sage and derives its name from the Latin 'salvere' (to save), so called because of the herb's ancient reputation for healing properties.

Growing to more than 3ft in height, Salvia divinorum ('sage of the seers') has large green leaves and white flowers and is native to the Mazatec region of southern Mexico. The native shamans have for centuries chewed the plant's leaves to induce visions as part of spiritual and healing ceremonies. It remained almost unknown outside the region until Daniel Siebert, a Californian ethnobotanist who was studying the use of herbs in spiritual traditions, came across the plant during his research in the Seventies. Today, it is sold as an extract: the '10x concentrate' is 10 times the potency of the unprocessed leaf.

For his part, Lee Hogan describes his first experience of salvia as the, 'most mind-bending, totally bizzarest, weirdest, strangest experience I have ever had'. It's difficult, he says, to explain the impact that the herb had on his brain. 'I was pulled to my right, into the brain-curve-warp-swirl tunnel is the best I can describe it,' he says. 'My brain, reality as we know it and everything else just sort of fused together and became this swirling tunnel. Endless, infinite. Speaking becomes very difficult, almost impossible.'

In a nod to some kind of 'code of conduct', there are two cardinal rules of the salvia world, and both are spelt out on all the websites and packaging: only take it when seated or lying down in a secure environment; and always have a sober sitter present to look after and reassure the taker.

Hogan insists that the effects are only at their most intense for 10 minutes and that, although the hallucinations can be disturbing, they don't do any permanent damage. But scientists disagree. Research has shown that the herb could trigger serious psychiatric problems. 'I am very concerned about the use and misuse of Salvia divinorum because it contains an active ingredient that can trigger hallucinations,' says Professor Fabrizio Schifano, an expert in drug addiction based at the University of Hertfordshire. 'For some vulnerable individuals, this may mean the onset of a psychotic episode.'

Kathy Chidester has no doubt that Prof Schifano's fears are justified. Three years ago, her 17-year-old son, Brett, committed suicide after smoking salvia.

'The fact that his posthumous drug test showed no signs of drugs led us to believe definitely that the drug had to be salvia, especially since that was all the police found with him. Since it metabolises within 15 minutes, there's no way it would show up on a drug test of any kind. These facts, not suppositions on our part, led us to believe 100 per cent that his salvia use led him to complete psychosis within the last hours of his life, and to his ultimate suicide.'

Soon after Brett's death, Delaware became the first state to impose a full ban on salvia, passing 'Brett's Law', legislation that places the plant in the same category as cocaine and heroin. The greatest concern is that salvia use could trigger mental health conditions such as schizophrenia, particularly among young people in their teens and twenties who may well be unaware that they are prone to psychotic episodes.

Sally D or Magic Mint, as aficionados know it, remains off the radar of most parents, health professionals and law enforcement agencies. But according to the first federal estimates, published last year, of salvia use in the US, about 1.8 million people had tried the drug, including 750,000 in the previous 12 months. Most strikingly, nearly three per cent of males aged 18 to 23, the largest category, had used salvia in the past year – nearly as many as had taken ecstasy and twice as popular as LSD. The US Armed Forces are developing the first urine tests for salvia amid reports about its presence on military bases and ships. And studies at some US universities concluded that up to 7 per cent of students had tried it.

The effect is indisputably mind-altering. But in the scientific, law-enforcement and drug-regulation fields, there is a growing controversy about how to handle salvia's soaring popularity. Is it a basically harmless plant that delivers an extremely strong but short-lived high, open to use and abuse like other low-level psychoactive drugs such as alcohol and nicotine? And would prohibition be a futile gesture, introducing another level of criminality while having little impact on its availability or popularity?

Or is it dangerous and harmful, risking bouts of psychosis in unwitting users? And should the drug be outlawed or restricted, as some US states have recently done, following Delaware's example?

Salvia divinorum has been outlawed or its sale and distribution restricted in Australia, Belgium, Denmark, Estonia, Finland, Italy, Japan, Spain and Sweden. Thirteen states in the US have also passed legislation that ranges from placing it in the most serious narcotics category alongside heroin and cocaine to outlawing its sale and distribution to minors under 18. US federal drug regulators have followed salvia's impact for several years but say they have yet to identify a convincing case to add it to the list of controlled substances. In the scientific community, there is concern that criminalisation could reduce access to the plant and the scope for research, but Californian Republican assemblyman Anthony Adams insists that medical research will not be affected by banning salvia.

He was first made aware of the drug in 2006 when police officers in his district told him they were increasingly finding students in possession of the herb during raids for other offences.

'It was clear to them that salvia was harmful, emotionally and possibly physically, and they were frustrated that there was nothing they could do,' he says. 'So they approached me to ask about the possibility of introducing legislation to ban it. Even if it's non-addictive, you lose your ability to reason, you are incapacitated, you cannot make informed decisions about your behaviour.'

He ran into opposition to calls for an outright ban in the Democratic-run state legislature so offered a compromise bill to make it illegal to sell or distribute the drug to minors. Mrs Chidester flew in to give her moving personal account and the legislation passed comfortably.