The most common side effects of fingolimod have been head colds, headache, increased gamma-glutamyl transfer (≤15%), diarrhea (13%), nausea (13%), abdominal pain (11%) and fatigue. A few cases of skin cancer have been reported, which has also been reported in patients taking natalizumab (Tysabri), an approved MS drug. Fingolimod has also been associated with potentially fatal infections, bradycardia and, in 2009, a case of hemorrhaging focal encephalitis, an inflammation of the brain with bleeding. Two people died: one due to brain herpes infection, and a second one due to herpes zoster. It is unclear whether the drug was responsible for the events. At least three cases of progressive multifocal leukoencephalopathy had also occurred as of 2015.