The problems that may be encountered by people with MS who stop taking natalizumab (Tysabri) have been well documented. It is likely that for many people stopping Tysabri, even if the drug has been working well in controlling disease activity, the disease reverts to how active it was prior to treatment (reactivation), and for some people, rebounds to even more active disease (rebound). Many people do elect to stop treatment, some because they test JC virus positive, others because they feel they have been on the drug for a long period, and want to reduce the risk of progressive multifocal leukoencephalopathy (PML). Researchers have been trying to develop some kind of treatment strategy when PwMS do stop Tysabri; one of these strategies has been to start Gilenya when stopping Tysabri. In this Italian study of 22 PwMS on Tysabri stopping the drug and taking Gilenya instead, reactivation occurred in 11 (50%) and rebound in three (14%). Given that not all of these people had MRIs, this might have underestimated the true incidence of reactivation and rebound. The conclusion of the researchers was that Gilenya doesn't become effective quickly enough for it to be used to prevent disease reactivation after stopping Tysabri. People with MS who take Tysabri and are planning to stop should discuss this in some detail with their doctors to ensure the best possible chance of keeping the disease under control when stopping.