TRENTON, N.J. (AP) — U.S. regulators have approved the first new drug in a decade for Parkinson’s disease, a chronic neurological disorder that causes tremors and movement difficulties.

The Food and Drug Administration said Tuesday that it has approved Xadago for use when a patient’s regular medicines aren’t working well.

The pill was tested in two six-month studies that included about 1,200 patients taking a standard treatment, levodopa.

According to the FDA, adding Xadago to levodopa decreased periods with troubling symptoms such as involuntary muscle movement. Patients who took Xadago also had better control of movement compared to groups that got levodopa and dummy pills.

Roughly 1 million Americans and up to 10 million people worldwide have Parkinson’s. It generally strikes the elderly, affecting 1 percent to 2 percent of those over age 65.