 A representative number of patients with baseline overactive bladder OAB symptoms and Parkinsons disease will be recruited to receive either the active drug or placebo for the first phase of eight weeks. The groups will then be crossed-over during the second phase of eight weeks. The main outcomes assessed will be the urgency episodes on a 3-day voiding diary, as well as the nocturnal sleep problems will be the Parkinsons Disease Sleep Scale PDSS. 