GlaxoSmithKline Plc said Thursday regulators approved the first U.S. treatment for Restless legs syndrome, a condition that can disrupt sleep and daily activities.

The neurological condition, which involves a compelling urge to move the legs, affects one in 10 adults in the United States and is the leading cause of insomnia.

Although its exact cause is unknown, researchers believe it may be related to dopamine, a chemical that carries the signals between nerve cells that control body movement.

Glaxo, Europe’s biggest drugmaker, said the drug Requip (ropinirole) works by stimulating dopamine receptors in the brain. The U.S. Food and Drug Administration approved the drug for use in moderate to severe cases of restless legs syndrome, or RLS.

Requip is already an established treatment for Parkinson’s disease.

In clinical trials for RLS, the most common side effects of Requip were nausea, extreme drowsiness, vomiting, dizziness and fatigue.

In December, a European Union panel of experts initiated a probe of the drug after concerns surfaced about the product’s effectiveness and long-term safety. Called Adartrel in Europe, the drug is sold in a few countries but has not yet received full European approval.

GlaxoSmithKline spokeswoman Holly Russell said the drug is still under review, but the company is confident it can address the issues that have been raised.