A murder trial has heard a woman allegedly poisoned her partner with a "cocktail of dangerous medication" so she could benefit financially from his death.

Key points: Prosecutors allege the cocktail of medication used to kill Mr Lawrence was prescribed to the accused

Prosecutors allege the cocktail of medication used to kill Mr Lawrence was prescribed to the accused They allege Ms Dent stood to gain financially from Mr Lawrence's death

They allege Ms Dent stood to gain financially from Mr Lawrence's death Defence lawyers told the court it was an accidental overdose

Wendie-Sue Dent, of Dapto in New South Wales, has gone on trial in South Australia's Supreme Court charged with murder.

The court heard her de facto partner, David Lawrence, died in his bed at Morphett Vale in Adelaide's southern suburbs in December 2015.

Prosecutor Emily Telfer told the jury that Mr Lawrence died from a toxic level of medication.

"It is alleged that Ms Dent murdered Mr Lawrence by poisoning him with a cocktail of dangerous medication which she possessed because it was prescribed to her for an ongoing pain condition," Ms Telfer said.

The court heard the medication included a strong opioid, Valium and morphine.

"The prosecution say that this was no accidental overdose, this was no suicide, this was a deliberate killing by the accused of David Lawrence because she stood to gain financially from his death," Ms Telfer said.

Ms Telfer told the jury police found a glass of orange liquid next to Mr Lawrence's bed and analysis of that liquid found traces of medication that had been prescribed to 61-year-old Ms Dent.

"The prosecution allege this is the way Mr Lawrence ingested the drugs that ultimately killed him," Ms Telfer said.

"That liquid contained traces of morphine, Tramadol and Valium, those three drugs, not prescribed to Mr Lawrence but available to Wendie Dent."

Sisters' names were spelled incorrectly, court told

The court heard Ms Dent was set to inherit Mr Lawrence's superannuation, which totalled about $300,000, as well as other assets.

"Only months after they met, David Lawrence signed a document which provided for the entirety of his superannuation money to be paid to Ms Dent if he passed away," Ms Telfer said.

Accused woman Wendie-Sue Dent in court in 2017. ( ABC News )

The court heard Mr Lawrence's family became suspicious after his death when Ms Dent showed them documents and handwritten notes purporting to be from Mr Lawrence indicating that he felt "his time was almost up" and he wanted his entire estate to go to Ms Dent.

The jury heard in some documents Mr Lawrence's sisters' names were spelled incorrectly.

The court heard expert handwriting analysis indicated that it was Ms Dent's handwriting.

Ms Telfer said friends and family had become concerned about Mr Lawrence when he failed to answer calls and text messages, including on his birthday which the court heard was likely the day before his death.

The court heard when paramedics went to the home after Ms Dent called triple zero saying she awoke to find her partner dead in bed, they discovered Mr Lawrence's cold body.

Death was 'accidental overdose', defence says

The accused's defence lawyer, Stephen Apps, told the jury that Mr Lawrence had decided to take Ms Dent's medication to try to get some pain relief from a very sore back.

"The defence will submit that he died of an accidental overdose," Mr Apps told the jury.

Mr Apps said his client was in a "very close and loving relationship" with Mr Lawrence and her life had "fallen apart" after his death.

"Over time, in the state that she was in, she said and wrote many things that were quite irrational," Mr Apps said.

"In a state of denial she was untruthful about some of the events that had happened."

Mr Apps said that included his client's denial of any knowledge of Mr Lawrence taking her prescription medication.

The court heard police telephone intercepts recorded Ms Dent telling friends that Mr Lawrence had died from asbestosis, which was untrue.

"She could not bring herself to accept that she had allowed Mr Lawrence to take the medication that may have resulted in his death," Mr Apps said.

"What Ms Dent said and did in those circumstances was unwise, obviously, but in summary, ladies and gentlemen, Ms Dent did not intend to harm her loved one in any way at all, she only wanted him to get better.

"Tragically and sadly it ended with an accidental overdose."

The jury is being taken on a view of the home where Mr Lawrence died. The trial is expected to run for four weeks.