Loughner has pleaded not guilty to 49 charges in the Jan. 8 shooting that killed six people and wounded 13 others, including Rep. Gabrielle Giffords, at a meet-and-greet event held by the congresswoman outside a Tucson grocery store.
U.S. District Judge Larry Burns said he won't second guess medical experts who concluded that Loughner's condition deteriorated in the weeks after an appeals court halted medication.
Burns said Loughner kept himself awake for 50 hours straight, often crying in his cell, before medications resumed.
Loughner has been at the Missouri prison since May after mental health experts determined he suffers from schizophrenia. Burns ruled him mentally unfit to stand trial.
He was forcibly medicated in June and July after doctors found he was a danger to others. An appeals court halted the medications while it considered an appeal of Burns' decision to allow the drugs. The appeals court has scheduled a hearing in San Francisco on Tuesday.
Loughner has been under suicide watch.
The Associated Press contributed to this report.