Cy Walsh entered his plea in the Adelaide Magistrates Court on Friday.
The 27-year-old is alleged to have murdered his father at the Walsh family home in July.
He has been committed to the Supreme Court and will appear there on February 1.
Prosecutor Lucy Boord told the court that a test for a particular drug was still underway.
“Forensic Science SA is testing for it now, and we intend to put all that fresh information before the Supreme Court,” she said.
Walsh appeared in court by video link from a secure mental health facility where he has been held since the alleged killing.
He made no comment during the brief appearance but seemed to follow the proceedings.
At a previous hearing the court was told that some witnesses in the case had gone to ground as the investigation continued.
It also heard that toxicology tests had been conducted on Walsh’s hair and the results of those tests were being subjected to expert analysis.
Boord told the court on Friday that the expert report on those tests had now been received.