Ujah was provisionally suspended after Ostarine and S-23 - substances prohibited by the World Anti-doping Agency (WADA) - were detected in his A and B samples following the men's 4x100m relay final in which Britain finished second behind Italy.
The AIU, which oversees integrity issues in international athletics including doping, added that the ban was effective from August 6th 2021 and will be in force until June 5th, 2023.
Ujah and his team mates Zharnel Hughes, Richard Kilty and Nethaneel Mitchell-Blake were stripped of their silver medal in February after a Court of Arbitration for Sport ruling. Canada were upgraded to silver and China to bronze.
"Obviously, I made a mistake," Ujah told The Guardian. "But people make mistakes. I am not a cheat."
The 28-year-old said a £10 supplement caused him to test positive for the prohibited substances.
"I think complacency set in. During the pandemic I relied a lot on Amazon, rather than using the people and resources around me," Ujah said.
"It was just convenient, with next-day delivery. And I didn't think anything was wrong with it."
UNCERTIFIED SUPPLEMENTS
Ujah had said he had "not knowingly or intentionally doped" but Kilty said in February that British Athletics and UK Anti-Doping had "hammered home" their rules, asking athletes not to use uncertified supplements.
"You know what? I wish I had been tested right before the Olympics, so that I never went," Ujah added.
"That way, I would never have put these other three guys, my team mates, through what they went through as well as myself."
UKAD said in a statement that the AIU announcement marked another sad chapter in the case and for sport in Britain.
"Every national governing body, athlete, coach and member of support staff should take this case as a warning that doping presents a threat to British sport at the highest levels," said UKAD Chief Executive Jane Rumble.
"This case underlines the need for all sports to redouble their commitment to their anti-doping responsibilities."
