Findings from a Phase II patient trial show that a high daily dose of simvastatin can stave off nerve damage linked to worsening symptoms. A month's supply of 20 milligram simvastatin costs less than £8.
Patients in the MS trial were randomly assigned to treatment with either an 80mg dose of the drug or a dummy placebo pill.
All 140 participants had secondary progressive MS, a form of the disease marked by worsening symptoms.
Over a period of two years, patients treated with simvastatin suffered 43% less brain shrinkage than those given the placebo.
They also achieved significantly better scores in movement tests and questionnaire-based disability assessments.
Previous research has linked increased brain wasting due to MS with greater disability.
More than 10,000 people in Scotland have the condition and the country has the among the highest rates of MS in the world.
Study co-author Dr Richard Nicholas, from Imperial College London, said: "At the moment, we don't have anything that can stop patients from becoming more disabled once MS reaches the progressive phase.
"Discovering that statins can help slow that deterioration is quite a surprise. This is a promising finding, particularly as statins are already cheap and widely used."
Statins are taken by millions of people to lower cholesterol and protect the heart, but why they should benefit MS patients is unclear.
One possibility is that they have an anti-inflammatory effect that may protect the nervous system.
An early clinical trial of simvastatin in people with early-stage MS showed some reduction in brain lesions, sites of nerve damage in the brain.
This suggested an effect on the underlying disease process, but subsequent trials have produced conflicting results.
The latest findings are published in The Lancet medical journal.
MS is an autoimmune disease in which myelin, the fatty insulating material that covers nerve fibres, is destroyed by the body's own defences.
Nerves lacking myelin are not able to transmit messages properly, leading to symptoms ranging from mild tingling or numbness to full blown paralysis.
In its progressive stage, MS causes the brain to shrink by about 0.6% a year.
Magnetic Resonance Imaging (MRI) brain scans showed an average atrophy rate of 0.3% a year in patients treated with simvastatin. After adjusting for factors such as age and gender, this amounted to a 43% reduction when compared with the placebo.