The International Tennis Integrity Agency (ITIA) announced the suspension of the 31-year-old following a positive test for benzoylecgonine, a cocaine metabolite, from a sample taken during an ATP 250 event in Mallorca in June.
Kyrgios, who reached a career-high rank of 13, has been provisionally suspended since August 4 after a World Anti-Doping Agency (WADA) laboratory confirmed the presence of the banned stimulant on July 17.
"I recently failed a drug test in Mallorca after testing positive for cocaine. I made a huge mistake, and I take full responsibility for it," Kyrgios said on Instagram.
"I'm sorry to my fans, my family, my sponsors and everyone close to me. Above all, I'm sorry to the kids who follow me. I know the example this sets and I'm deeply disappointed in myself."
Cocaine is classified as a stimulant and substance of abuse on the WADA Prohibited List and is banned in competition under tennis anti-doping rules.
Kyrgios said he made no excuses but painted a picture of a player struggling with the twilight of his career, citing the mental toll of recent injuries.
"I do want to give some context about where I've been. The last couple of years of injuries have taken a huge toll on me, both physically and mentally," he added.
"My body hasn't been able to do what my mind expects it to do, and coming to terms with being near the end of my career has been harder than I ever imagined.
"I've always said I didn't choose tennis - tennis chose me. But letting go of something that has been my whole life is one of the hardest things I've ever had to face. At times I've felt helpless and alone."
While suspended, Kyrgios cannot play in, coach at, or attend any events organised by World Tennis, WTA, ATP, the Grand Slams, or any national association.
The Australian has not appealed the provisional suspension and said he would step away from social media and public life for 28 days to "focus on getting myself right."
"I'm sorry. I'll do the work and come back better," he concluded.