There are growing concerns about the side-effects of a top-selling anti-psychotic, with ambulance call-outs for emergencies involving the drug skyrocketing over the past decade.

Quetiapine, commonly marketed as Seroquel, has become a blockbuster pharmaceutical both in Australia and internationally.

Despite being an anti-psychotic drug, meant initially to be used to treat only serious conditions such as schizophrenia and bipolar disorder, it has become one of the highest-selling medications of any kind.

The drug is increasingly being prescribed for a range of conditions - anything from sleep disturbance to anorexia - but there is a growing body of concern about the harmful and disturbing side-effects it can cause.

Musician Heidi Everett has been on Seroquel, which acts as a powerful sedative, for a decade.

She started on a dose of 1,000 milligrams a day - more than three times the daily dose recommended by Australia's Therapeutic Goods Administration.

"I was in a chemical straitjacket. I was a zombie for 24 hours a day, sleeping incredibly long. When I did finally get out of bed, it was a struggle to get to the kitchen," she told 7.30.

"And then what happens on Seroquel is that it freezes your muscles and shuts your muscle system down. So, it's really hard to walk. And when I did walk I had no control over my ability to stop walking, so I walked into walls."

Ms Everett also developed a heart condition, known as tachycardia.

"It's where your heart starts beating extremely fast and out of control. And I don't mean just a little flurry, I mean for two or three hours of extreme ... heart rate," she said.

'There have been recorded deaths'

Matthew Frei, the clinical director at Melbourne's Turning Point Drug and Alcohol Centre, says he has seen some worrying developments with the drug over the past few years.

"We were seeing people getting toxicity from the drug. So that's things like over-sedation, collapse, and even over-dosage where people required admission to hospital," he said.

"There have been recorded deaths as well."

He asked epidemiologist Belinda Lloyd to look into ambulance data to see how often the drug was showing up.

"We examined quetiapine-related ambulance attendances over a 10-year period," Ms Lloyd said.

"And looked at those in the context of other drugs that are used for the same purpose and in the same drug group. And what we found was a really substantial increase over the decade in people being attended by ambulance as a result of inappropriate quetiapine use."

In the decade to 2011, ambulance attendances for emergencies associated with the drug rose from 32 a year to 589 a year - something not seen with other similar anti-psychotics.

Victorian Coroners Court statistics for the past three years show it contributed to 10 per cent of drug deaths.

Mr Frei says a black market in the drug has emerged.

"People prescribed the drug [are] giving it, selling it, trading it with friends who aren't prescribed the drug," he said.

Questions over soaring rate of prescriptions

Seroquel, sold by pharmaceutical giant AstraZeneca, initially excited the medical community as it seemed a promising alternative to more addictive sedatives like Valium.

Medicare statistics show that in Australia, the prescribing of Seroquel grew from about 1,500 scripts a year in 2000 to almost a million by the end of last year.

The trend is not mirrored by other anti-psychotics, and forensic psychiatrist Erik Monasterio from the University of Otago says that raises questions.

"How has it come about that a medication that's designed for the treatment of a very rare condition has become so popular? That is the ultimate question that needs to be answered," he said.

University of Sydney psychopharmacologist Professor Iain McGregor has charted the explosion in use of the drug for a host of maladies for which it is not approved or intended.

"We see quetiapine being used in anxiety, it's used in depression, it's being used for insomnia, it's used a lot in people who have drug and alcohol problems, it's used in things like anorexia nervosa," he said.

"Just about any condition where there's an emotional problem, you'll find quetiapine being used these days.

"I think of it as the Swiss Army Knife drug ... it has all these different tools within the one tool for different applications."

Until last year, Seroquel was the fifth-largest selling pharmaceutical of any kind, generating $6 billion in global sales for its manufacturer, AstraZeneca.

In 2012, the patent for Seroquel expired and AstraZeneca's sales plummeted. But it is estimated that sales of the generic drug quetiapine have only increased since then because it is so much cheaper.

AstraZeneca says Australians benefit from drug, champions its appropriate use

In the United States, AstraZeneca has been hauled through the courts.

In 2010, the company paid $520 million for marketing the drug off-label and for the debilitating side-effects patients experienced.

"It came to light that during the approvals process, AstraZeneca covered up some of the major side-effects of Seroquel in order to get it easily approved," Professor McGregor said.

In a statement to 7.30, AstraZeneca says it does not promote the off-label use of Seroquel.

"Quetiapine fumarate is a proven and effective medicine for its registered indications of schizophrenia, bipolar disorder, major depressive disorder and generalised anxiety disorder," the statement said.

"The medicine has been independently reviewed and licensed by the Therapeutic Goods Administration for these conditions. It is a fact that thousands of Australians have benefitted for being able to access this treatment for what are often difficult and complex mental health disorders.

"Our focus is to support prescribers to champion the appropriate use of medicine and ensure that patients receive this treatment only when there is a clear medical rationale for doing so.

"AstraZeneca does not promote or condone any use of quetiapine fumarate which is not consistent with the registered or approved indications."

Side-effects include weight gain and diabetes

In its US television commercials, AstraZeneca now includes long disclosures about a whole range of side-effects caused by the drug.

"Elderly dementia patients taking Seroquel XR have an increased risk of death. Call your doctor if you have fever, stiff muscles and confusion," one commercial said.

The biggest side-effect is explosive weight gain and diabetes.

"I was about 60 kilos before I was diagnosed and I went up to about 120 kilos afterwards," Ms Everett said.

The worst of the side-effects is, of course, death. Quetiapine has been associated with sudden heart failure.

A study in the Lancet medical journal tracking quetiapine patients in Finland over 10 years found some disturbing trends.

"They were more likely to be dead after 10 years than patients who were on other anti-psychotic drugs and there was also an increased risk of suicide as well," Professor McGregor said.

"This is one of the ironies with this massive increase in the prescription rate in Australia - when you stack it up against other medications and other treatments, it doesn't really stand out as a particularly good drug."

Patients should be aware that coming off quetiapine abruptly is not recommended and could cause side-effects. Anyone wishing to change their psychiatric medication should first consult their doctor.