Widely prescribed anti-cholesterol drugs are being tested to see whether they could be used to help treat multiple sclerosis (MS).
Experts have launched an assessment to see whether cheap statins may become an MS treatment as well as lowering cholesterol.
The six year trial will involve 1,180 people with secondary progressive MS at almost thirty centres across the UK, with the first participants starting medication later this year.
The £6 million project will test simvastatin in people with the secondary progressive form of MS.
People with this form of MS have limited options as there are currently no licensed treatments that can slow or stop disability progression.
MS affects more than 100,000 people in the UK.
The majority of people who are diagnosed with the condition are told they have relapsing MS and around half of those patients will develop secondary progressive MS within 15 to 20 years.
Lead researcher Dr Jeremy Chataway from University College London's Institute of Neurology, who led an earlier study into the drug, said: "This drug holds incredible promise for the thousands of people living with secondary progressive MS in the UK, and around the world, who currently have few options for treatments that have an effect on disability.
"This study will establish definitively whether simvastatin is able to slow the rate of disability progression over a three year period, and we are very hopeful it will."
A small study involving 140 people with secondary progressive MS, which was published in The Lancet in 2014, found those taking high doses of the drug had a significant reduction in the rate of brain shrinkage over two years and also had better disability scores at the end of the study.
Michelle Mitchell, chief executive of the MS Society, which is part-funding the trial, added: "This is a momentous step forward in our quest to find an effective treatment for progressive MS.
"More than 100,000 people in the UK are living with MS and this research will offer a huge amount of hope to the majority of them."
MS is a condition of the central nervous system. People typically start experiencing symptoms in their 20s and 30s, which include fatigue, sight loss, incontinence and disability.
Secondary progressive MS patient Stuart Nixon added: "At the moment people like me are living with the prospect of our condition getting worse each day. This is the most exciting opportunity to change how we manage progressive MS.
"It would be amazing if this trial can show that an existing drug, costing just a few pence a day, can help with MS."