The Queensland Reds front row tested positive for the banned substance twice and has been fined £15,000 whilst also being handed the minimum mandatory suspension in Rugby Australia's illicit drugs policy.
It is a huge disappointment for the 28-year-old, who has been capped 86 times for the Wallabies, and he admits he needs to tackle his depression issues head-on.
"I have been suffering wellness issues, including depression, for a year and have been receiving professional assistance for the last few months," Slipper was quoted as saying by BBC Sport.
"In no way do my personal circumstances excuse my actions but I recognise now that I was not coping and that I need to properly address these wellness issues."
RA chief executive Raelene Castle also reacted to the news, saying: "We are extremely disappointed to be in this position today. James has expressed his sincere remorse.
"We are fully aware that he is dealing with very significant personal issues and we have been working with him since February on these matters."