Patients prescribed drugs for movement disorders - including restless leg syndrome (RLS) - say doctors did not warn them about serious side effects that led them to seek out risky sexual behaviour. Twenty women have told the BBC that the drugs - given to them for RLS, which causes an irresistible urge to move - ruined their lives. A report by drugs firm GSK - seen by the BBC - shows it learned in 2003 of a link between the medicines, known as dopamine agonist drugs, and what it described as deviant" sexual behaviour. It cited a case of a man who had sexually assaulted a child while taking the drug for Parkinson's. Some of the women who described being drawn to risky sexual behaviour told us they had no idea of what was causing it. Others said they felt compelled to gamble or shop with no history of such activities. Impulsive behaviours, including gambling and increased sex drive, have long been listed as side effects in medicine leaflets for dopamine agonist drugs - and are thought to affect between 6% to 17% of RLS patients taking them, according to health guidance body NICE. The cases of what the GSK report from 2003 described as "deviant behaviour" involved two men who were prescribed Ropinirole for Parkinson's disease. In one, a 63-year-old-man sexually assaulted a seven-year-old girl, leading to a custodial sentence. In the second case, a 45-year-old man carried out "uncontrolled acts of exhibitionism and indecent behaviour".