Maree Mavis Crabtree is alleged to have killed 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.
 The jury heard that Jonathan's sister Tara, who had been granted immunity from prosecution, would testify her mother hid a lethal amount of painkillers in a fruit smoothie while she kept watch.
Defence barrister Angus Edwards in his opening address said Tara would admit lying to police.
"That is the real issue in this trial: do you believe Tara Crabtree's story of murder committed by her mother?" Mr Edwards said.
Two-and-a-half years after Jonathan's death, Tara had told police a different version of what happened and had accused her mother, the jury heard.
"What are her motives when she came out with this story about her mother? Is something sinister going on here?" Mr Edwards said.
"Has it helped her with property or financially? Was she looking at the family home?"
A pathologist determined the cause of Jonathan's sudden and unexpected death was an excessive amount of the drug oxycodone in his bloodstream, crown prosecutor Caroline Marco told the jury.
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 Tara Crabtree would also testify about hearing her brother struggling and coughing throughout the night after having the drink.
"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 requiring 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.
Jonathan could have given himself an accidental or deliberate overdose while living in a house where people were taking multiple kinds of drugs, Mr Edwards told the jury.
The trial is due to run for five weeks before Justice Martin Burns and hear from 60 witnesses.
Lifeline 13 11 14
beyondblue 1300 22 4636
16°C