"The trial, called CLARITY, was a two year study involving 1,326 people with relapsing/remitting MS receiving one of two doses of cladribine or an inactive placebo.
During the study, people receiving the lower dose of cladribine experienced a 58% reduction in relapse rates compared to the placebo group (an average of 0.14 relapses compared to 0.33). Side effects included lymphopenia, a reduction in white blood cells, headaches and nasopharyngitis (a cold)."