A mother gave her adult son a lethal smoothie following disputes over money and the family's intolerable living situation, a jury has been told.
Maree Mavis Crabtree has been accused of killing her 26-year-old son Jonathan with an overdose of painkillers on July 19, 2017 in the family's home north of the Gold Coast before making a $125,000 insurance claim.
The 59-year-old has also been accused of attempting to murder her son in January of the same year.
Crabtree pleaded not guilty to the murder, attempted murder and fraud charges when her trial began at Brisbane Supreme Court on Tuesday.
Her son was found dead by paramedics while lying on his bed at 9.55am with his legs hanging down to the floor and a Spider-Man backpack at his feet, crown prosecutor Caroline Marco told the jury.
"A pathologist determined the cause of his sudden and unexpected death was an excessive amount of the drug oxycodone in his bloodstream," she said.
Investigators did not find the prescription painkiller or related packaging in the son's room or among his other drugs in the Spider-Man pack.
"The Crown will prove it was his mother who killed him by deliberately giving him a drink in the form of a shake that she prepared with a blender in the kitchen of their home that contained the oxycodone that killed him," Ms Marco said.
The jury was told they would hear from Crabtree's daughter Tara, who would testify that she helped her mother by keeping a lookout as she prepared the drink and of later hearing the son struggling and coughing throughout the night.
"Tara will tell you the next morning her mother told her Jonathan was dead but it was four hours later that (Crabtree) called triple zero," Ms Marco said.
"Tara says that was not the first time that her mother had given a drink to Jonathan containing oxycodone with the intent of ending his life."
Jonathan Crabtree was a "troubled man" with abusive behaviours who used drugs and had been charged with robbing a chemist, the jury heard.
A car crash in 2015 had left him with permanent injuries that meant he required physical care.
Crabtree lived in the Maudsland home that was jointly owned by her two children.
"She told Tara that Jonathan's involvement in the robbery had put the family's finances in jeopardy, which was the reason why she needed to kill him," Ms Marco said.
Crabtree found her living situation with her son "no longer tolerable" but she did not have the money to buy out his stake of the house, the jury heard.
Investigators found numerous bottles of liquid oxycodone in the family's home and a smoothie blender that tested positive for drugs, Ms Marco said.
Defence barrister Angus Edwards was expected to make an opening statement.
The trial is due to run for five weeks before Justice Martin Burns and hear from 60 witnesses.
