The 32-year-old, who won 20 caps for Northern Ireland, was sent home from a squad in 2005 after breaking a curfew ahead of games against Azerbaijan and England to go drinking with team-mate Phil Mulryne.
But it was after moving from Sunderland to Cardiff in 2005 that he began to use class A drugs.
"I'd been on humongous benders. It wasn't just alcohol, it was cocaine and a mixture of other drugs," he told BBC Radio Manchester in an interview to be broadcast on Thursday.
"The cocaine just enabled me to drink more. From being so drunk, to then having some cocaine, and then being able to go another two or three days.
"I remember Dave Jones (Cardiff manager at the time) at one point said to me 'Jeff, don't come in but we'll still pay you' (because of his drinking).
"I never took any other drug apart from alcohol and cigarettes when I was playing at the time. When Dave Jones said that to me I thought 'I've never tried cocaine, I'd give it a blast' and when I did I thought 'wow, this is what I'm missing'.
"I was hooked that quick. If you're an addict you can get hooked on computer games, texting, eating. it doesn't matter what it is.
"When it comes to class A drugs then you're in trouble."
Whitley played for Stoke and Wrexham on loan while at Cardiff before later joining Wrexham on a permanent basis.
He represented Woodley Sports and Northwich in the final year of his 13-year career, has confronted his demons during a spell in the Sporting Chance Clinic and is now sober.