SYDNEY (Deutsche Presse-Agentur (dpa)) -- Giving ketamine to help relieve the suffering of dying cancer patients is worse than useless.

Those taking ketamine reported toxic side-effects like dizziness and confusion at twice the rate of those who took standard medications like the opiate morphine and over-the-counter analgesics like paracetamol, Australian researchers have found.

"You'd have to treat 25 people before one person gets an additional benefit from it and you'd only have to treat six people before you found one with toxicity such that you'd have to stop the medication," professor David Currow said. "It's right round the wrong way."

A popular but illicit recreational drug because of the spacey state it induces in those who take it, Ketamine is used as a strong pain-killer in emergency medicine. Sold under the trade name Ketanest, Ketaset and Ketalar, it is also widely used in veterinary medicine.

The researchers took 185 volunteers with advanced cancers who were being treated for chronic pain. Half were given ketamine and the other half were given a placebo in a double-blind, randomized trial over five days.

On the first day, twice the incidence of side-effects were reported in the ketamine group as in the placebo group and the severity of toxicity increased as the days piled up.

"Those who got the placebo got exactly the same response rate as those who got ketamine," Currow said. "What it tells us is that the best evidence we have in the world today is that there's no net benefit to the use of ketamine in this patient population."

Currow's research is reported in the Journal of Clinical Oncology.

Copyright 2012 dpa Deutsche Presse-Agentur GmbH