DEA San Diego Acting Special Agent-In-Charge William R. Sherman said in a statement that he was troubled by the treatment of Daniel Chong and extended his "deepest apologies" to him.
The agency is investigating how its agents forgot about Chong.
Chong, 23, was never arrested, was not going to be charged with a crime and should have been released, said a law enforcement official who was briefed on the DEA case and spoke on the condition of anonymity.
Chong told U-T San Diego that he drank his own urine to survive and that he bit into his glasses to break them and tried to use a shard to scratch "Sorry Mom" into his arm.
The engineering student at University of California, San Diego, was swept up as one of nine suspects in an April 21 drug raid that netted 18,000 ecstasy pills, other drugs and weapons.
Chong said DEA agents told him he would be released. One agent even promised to drive him home from the DEA field office in Kearny Mesa, he said.
Instead, he was returned to a holding cell to await release. He also said the lights went off at one point and stayed off for several days.
Sherman says the event is not indicative of the high standards to which he holds his employees. He says he has personally ordered an extensive review of his office's policies and procedures.
Chong said he could hear the muffled voices of agents outside his windowless cell and the sound of the door of the next cell being opened and closed. He kicked and screamed as loud as he could. His cries for help went unheard.
"I had to recycle my own urine," he said. "I had to do what I had to do to survive."
When he was found on April 25, he was taken to a hospital and treated for cramps, dehydration and a perforated lung - the result of ingesting some of the broken glass.
"When they opened the door, one of them said: `Here's the water you've been asking for,'" Chong said. "But I was pretty out of it at the time."
Chong also ingested a white powder DEA agents said was left in the cell accidentally and later identified as methamphetamine. He described having hallucinations, saying: "I was completely insane."
Chong's attorney, Eugene Iredale, said he plans to file a claim against the federal government and, if it is denied, he will proceed with filing a federal lawsuit.