The Food and Drug Administration approved Sanofi’s multiple sclerosis drug Aubagio late Wednesday for adults experiencing flare-ups of the neurological disorder.

The once-a-day pill is the first Genzyme drug to win approval since Sanofi acquired the drugmaker for $20 billion last year. Genzyme, which is based in Massachussetts, specializes in very expensive biotech drugs for rare diseases.

Multiple sclerosis causes the body’s own cells to attack the nervous system, affecting the brain and spinal cord. Symptoms can include muscle spasms, trouble walking, dizziness, facial pain and other problems. Most patients experience a relapse of symptoms followed by recovery periods. However, recovery periods can become shorter over time, leading to steady decline.

FDA said patients tested with Sanofi’s drug had a 30 percent lower rate of symptom relapse compared to patients taking a placebo.

The most common side effects recorded in patients were diarrhea, nausea and hair loss.

U.S.-traded shares of Sanofi, which is based in France, dipped 16 cents to $43.10 Thursday morning.