The Food and Drug Administration’s Center for Drug Evaluation and Research is investigating whether patients using certain organ transplant drugs, including CellCept (mycophenolate mofetil), a drug sometimes taken by lupus patients, are succumbing to an often-fatal neurological disease.

The pharmaceutical company responsible for CellCept, Roche, alerted the Food and Drug Administration (FDA) in November about the complication, reports the Associated Press (AP). The other drug the FDA is investigating: Myfortic (mycophenolate acid), made by Novartis.

Progressive multifocal leukoencephalopathy (PML), the neurological disease in question, attacks the brain and central nervous system. Doctors and patients using either drug are encouraged to keep an eye out for symptoms, which include vision problems, loss of coordination and memory loss.

Roche reports 10 cases of PMM since the drug was first released in 1995, the AP reports. More than 500,000 patients have used the drug.

The FDA will review new labeling for the drug, a process it expects to take two months.