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The cases of what the GSK report from 2003 described as "deviant behaviour" involved two men who were prescribed Ropinirole for Parkinson's disease.

The documents said the perpetrator's libido had increased significantly from the start of his treatment with Ropinirole and his "libido problem subsequently resolved" after his dose was reduced.

His sex drive was reported to have increased prior to being prescribed Ropinirole but his urges "intensified" after the treatment.

They said Ropinirole led to gambling debts and broken relationships.

In a statement, GSK told the BBC Ropinirole had been prescribed for more than 17 million treatments and undergone "extensive clinical trials".