Akhtar, 31, and new-ball partner Mohammad Asif tested positive for the banned steroid nandrolone in tests conducted by the Pakistan Cricket Board (PCB) in October last year. They were banned for two years and one year respectively in November.
However, a month later, both were controversially reinstated by a Pakistani appeals committee, prompting the World Anti-Doping Agency to go to the Court of Arbitration for Sport (CAS).
But, on Monday, CAS, based in Lausanne, Switzerland, ruled it did not have the jurisdiction to deal with the matter and that the PCB does not provide a right of appeal to the international sports court.
Akhtar said he was glad a difficult period in his life was now finished.
"I've had lots of controversies, mental problems, health problems, injuries - yeah I'm glad to be over them now. I've fixed myself once again," Akhtar told the Bigstarcricket website on Thursday.
"The Court's decision was a relief. Those times when I was banned were the darkest of my life, as I was in such agony and pain and mental stress," added Akhtar, nickamed the 'Rawalpindi Express'.
"But I have never taken illegal substances, I never did anything wrong."
Akhtar and Asif were omitted from the Pakistan squad that suffered a first-round exit at the World Cup, where coach Bob Woolmer was declared dead 24 hours after the team's shock defeat against Ireland in Jamaica on March 17.
"The way the doping case was handled was stupid and pathetically wrong," said Akhtar. "They (the PCB) could have saved their country's respect and a big disaster because the two of us lost our fitness and never ended up going to the World Cup."
He added: "The last four years for Pakistan cricket have been ballistic with The Oval fiasco (where Pakistan forfeited a Test against England in 2006 after being charged with ball-tampering), my doping fiasco, it was too much for Pakistan cricket to handle.
"Now the Pakistan team is recovering and we would like to do well once again."
In his 43 Tests Akhtar, who made his debut in 1997, has taken 169 wickets at an average of 25.30 apiece.