Johns also admitted he has an alcohol problem and is battling depression.
His startling revelations follow his arrest in London on Sunday for possession of an ecstasy tablet.
Johns, nicknamed ‘Joey’ in his pomp, originally confessed to having the tablet in his pocket and said he planned to get rid of it.
But in an interview with his former New South Wales coach Phil Gould on Thursday night’s Footy Show – a rugby league programme on Australian TV station, the Nine Network – the former champion halfback admitted he would have swallowed the tablet and had used ecstasy extensively in the past.
“I’ll put my hand up – I was going to take it,” a visibly shaken Johns said.
“It’s happened before. People have given me ecstasy before.
“For 10 years I’ve taken it on and off, generally during the off-season.
“There’s times during the season when I’ve run the gauntlet and played Russian roulette and taken them.
“There were times when we’d be playing the biggest game of the season and it (taking ecstasy) would be in the back of my mind.
“I wouldn’t say I had a drug dependency – I do it occasionally – (but) I had an alcohol problem.
“I used it (ecstasy) to escape the pressure.
“I don’t want to make excuses. I’ve put my hand up. I’ve done the wrong thing and I’m so ashamed of it.”
Johns conceded his family, the Knights club and team-mates were aware of his drug problem.
He said he feared the day the drug testers would catch up with him.
“People probably ask how you avoid the drug testers – but if you play Friday night, don’t train Saturday, Sunday, then generally it’s out (of your system) by Monday,” he explained.
Johns admitted to battling depression throughout his career and has been on medication for the past five years.
“I didn’t want to take it because it stabilised me and took away the incredible highs, but invariably after the highs I’d crash to the lows where I couldn’t leave the house for four days,” he said.
“One minute I could be willing to take the world on – and that’s when I’d be at my creative best – but one day I could turn out on the field and not want to talk to anyone.”
The league superstar almost broke down when he told of the pain and shame he felt when he told his seven-year-old son, Samuel, about his drugs bust.
Johns also described his experiences in custody.
“I was in jail for six hours,” he said. “It was probably the scariest moment of my life.
“I was in a cell by my own but in the other cells there were a couple of crazy men just running and charging into the walls and screaming.
“It really shook me up. It really scared me.”