When Freddie’s dad Bill is diagnosed with Parkinson’s, his medication gives him a new lease of life. He starts ticking things off his retiree bucket list - travelling, skydiving, golf.

But then Freddie notices that his previously sensible father has started behaving unusually.

BBC Investigations correspondent Noel Titheradge has spent more than a year speaking to people whose behaviour changed radically after taking a category of prescription drugs called dopamine agonists.

These drugs boost dopamine activity in the brain - they were prescribed more than 1.5 million times in the UK last year to treat Parkinson’s disease and other movement disorders.

But they have well established side effects - around 1 in 6 people who take them develop impulse control disorders, which can include hypersexuality, binge eating, compulsive gambling and shopping.

If these side effects have been known about for decades, why weren’t some patients and their families properly warned or monitored?

Details of organisations offering help and support with some of the issues raised are available at bbc.co.uk/actionline.

If you have any concerns about medication you’re taking, speak to your doctor.

Presenter: Noel Titheradge