A drug used for Parkinson’s disease has been shown to be effective in reducing the symptoms of difficult to treat depression, according to a study led by the University of Oxford.

In the largest clinical trial to date, pramipexole was found to be substantially more effective than a placebo at reducing the symptoms of treatment-resistant depression (TRD) over the course of nearly a year, when added to ongoing antidepressant medication.

The trial, published in The Lancet Psychiatry, included 150 patients with treatment-resistant depression, with equal numbers receiving 48 weeks of pramipexole or a placebo, alongside ongoing antidepressant medication.