Alex Reuben McEwan had been on trial in the Brisbane Supreme Court after pleading not guilty to murdering 22-year-old Eunji Ban in Brisbane's CBD during the early hours of November 24, 2013.
Expert psychiatrist Dr Donald Grant testified that the 23-year-old experiences treatment-resistant schizophrenia and is on high doses of three types of antipsychotic medication.
After deliberating for four hours, the jury came to the conclusion that McEwan is not of "sufficiently sound mind" to continue a trial.
His fate may be determined in another trial at a later date.