A controversial drug hailed for its benefits for multiple sclerosis sufferers, but which carries a risk of a fatal brain disease, will undergo hearings this week to see if it should again be sold.

Tysabri, produced by Cambridge, Mass-based Biogen IDEC and Elan Pharmaceuticals of Ireland, was pulled off the market a year ago after three patients developed a rare disease. Two of them died.

The drug had been sold in the U.S. but was available only in clinical trials in Canada.

Multiple sclerosis is a chronic disease of the central nervous system. There is no cure, but treatments can stop or slow its progression. Symptoms include trouble with vision and walking, weakness, numbness and pain.

Several studies have confirmed Tysabri is effective, but comes with risks -- a dilemma common to many new medications.

"What I've learned in medicine is that you never get great benefit without some risk," Dr. Paul O'Connor of Toronto's St. Michael's Hospital told CTV.

The reports in last week's New England Journal of Medicine found Tysabri alone or with standard interferon treatment cut the rate of relapse by as much as two-thirds after two years and significantly reduced the progression of the disease, compared to those on a dummy treatment or interferon alone.

The drug is twice as effective in reducing attacks compared to medication currently available, O'Connor said.

Many multiple sclerosis patients, aware of the one-in-1,000 chance of developing the brain disease, want the drug brought back.

"It makes me feel like I am kicking (multiple sclerosis) in the butt," said Mel Grant, a patient who joined a study of the experimental drug.

"My symptoms improved quite a bit during the first few infusions that I had of Tysabri."

Added O'Connor: "Their energy is improved, their quality of life is improved. They feel better on the medication and they're willing to take that risk."

When regulators gave Tysabri fast-track approval in November 2004, doctors hailed it as a wonder drug.

However, the manufacturers voluntarily pulled the medication off the market about three months later. The deaths of two patients in clinical trials, who died of a rare brain disease called progressive multifocal leukoencephalopathy, triggered the decision.

Grant didn't see the withdrawal of Tysabri as a good thing.

"Some of my symptoms returned when I went off the drug and some new ones cropped up," she said.

"Personally yes, I'd like to get back on the drug."

The U.S. Food and Drug Administration advisory panel is holding its two-day public meeting in Gaithersburg, Maryland on Tuesday and Wednesday.

With a report from Avis Favaro