The 29-year-old tested positive for the drug on two separate occasions earlier this year. He was given the minimum mandatory two-month ban in May and fined A$27,500.
"I let a lot of people down and I couldn't be more sorry for that and more embarrassed for what I've done," a contrite Slipper told reporters ahead of his return to the field on Friday for a Super Rugby selection against the Wallabies.
"I've obviously gone through a bit of a rough patch and made some poor decisions and probably wasn't coping with certain aspects of my life that I was going through at the time.
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"At the end of the day it brought it to a head and I've addressed quite a few things and it's probably something that's going to have to stay with me for a while."
The loosehead prop, who has won 86 caps for Australia, said in May that he had been battling depression, but his enforced break had allowed him to confront his mental health issues.
"It forced me to actually have a real good look at myself and seek professional help," he added. "I was one of those blokes who didn't want to talk, simple as that.
"I clearly was struggling a bit there but as soon as I opened up to my mum and my dad and told them I was struggling it kind of lifted a weight off the shoulders and I could really address the issues."
Slipper's ban ended on July 15 and he was named in the Queensland Country team for Australia's third tier National Rugby Championship that starts on Sept. 1.
He was called into John Manenti's Super Rugby selection on Tuesday for their clash with the Wallabies at Leichhardt Oval in Sydney in a match the national team are using to prepare for the southern hemisphere's Rugby Championship that starts on Aug. 18 against the All Blacks.
"I'm just so lucky to be back here and given an opportunity to play against the Australian team, whether I play many minutes or not," Slipper said.
"But it'll be interesting. I feel like it's important just having that purpose and having a bit of drive in your life."
(Reporting by Greg Stutchbury; Editing by Amlan Chakraborty)
