A best-selling children's author has revealed how prescription drugs left her battling a compulsive shopping addiction that saw her blow more than £500,000.

Sally Gardner spiralled into reckless spending after being prescribed dopamine agonist drugs for Restless Legs Syndrome, splashing out on luxury items including a £3,000 bathtub, designer prints and repeated purchases of the same goods. 

At the height of her success, Gardner, who has sold 2.5 million books and won the Carnegie Medal, initially believed her lavish lifestyle was simply down to finally earning good money.

'Suddenly, I am in a different place,' Gardner said, 'and for the first time in my life, earning really well.' 

But behind the scenes, her spending quickly escalated. She began hiding purchases, lying to friends and racking up debts that eventually forced her to sell her north London townhouse and move into a smaller flat. 

'I had no idea what had happened to me. It was like, "Who are you? What are you doing?", Sally told hosts of the BBC podcast Ready to Talk.

Even then, what she describes as the 'drumbeat' of her compulsive behaviour did not stop, with tens of thousands spent on an interior designer.

At one point, a concerned friend even went from shop to shop asking staff not to sell her anything. 

Gardner said she believed she was 'going mad', unaware the medication she had been prescribed could trigger such side effects. 

Dopamine agonist drugs are widely used to treat conditions including Parkinson's disease and Restless Legs Syndrome by boosting dopamine activity in the brain. 

But the drugs have been linked to impulsive behaviours including compulsive shopping, gambling and hypersexuality, with some patients racking up huge debts or suffering broken relationships. 

Gardner said she repeatedly bought the same items, including five identical pairs of shoes and ten dog beds for her Yorkshire Terrier, chasing a dopamine hit. 

'You buy one thing and you get a dopamine hit from it and want that feeling again and again,' she explains. 

Her case is among hundreds highlighted by the BBC, with patients or their families describing devastating consequences. 

Many said they did not make the connection between their behaviour and the drugs until it was too late. 

The issue is now being reviewed by the UK's Medicines and Healthcare products Regulatory Agency. 

Gardner, who only realised the cause years later after listening to a BBC podcast, said she feels her life had been 'hijacked' by the medication. 

She has since reduced her dosage but remains on the drugs as they are the only treatment that works, and says she continues to battle the urges daily.

It comes after earlier this year the widow of a Parkinson's sufferer told how her husband was changed into a 'sex addict' overnight by one of his prescribed drugs.

Jane Ryde said he began collecting pornography and demanded sex at least three times a day – compulsive side effects which carried no significant warning on leaflets accompanying the drug Pramipexole.

She said that although it helped his disease symptoms, he would have been 'horrified' to discover what it was doing to him.

'He changed overnight into someone I didn't recognise,' she said.

'He was a hard-working man and he just became a sex addict I suppose - very compulsive behaviour collecting porn snippets and pornography.

'He couldn't see what the problem was. I ended up trying to talk to him about it and it just ended up in arguments so I then decided to keep a diary of everything that was going on.

'…The consultant just told him it was unacceptable behaviour and that was the end of the matter as far as the consultant was concerned.'

She told BBC Radio 4's Today programme that he began staying up until 1.30am – 2am surfing the internet.