Megan Jayne Somerville: Adelaide mum accused of repeatedly stabbing her kids in late-night attack on the North-South Motorway allegedly fuelled by drugs

A mother accused of stabbing her two young children was allegedly high on a cocktail of meth, cannabis and prescription medication at the time, a court has heard.

Megan Jayne Somerville, 37. appeared in Adelaide's Supreme Court via videolink on Monday from a closed mental health facility.

Somerville has been detained at the facility since the alleged attempted murder of her sons, aged three and eight, on the city's North-South Motorway on August 15, 2022.

Emergency services were called to the motorway at about 11.30pm following reports Somerville had been detained by members of the public who had intervened.

It's alleged Somerville had pulled over her silver Honda sedan, removed her children from the car and stabbed them 'a number of times' with a knife. 

The boys were rushed to the Women's and Children's Hospital in Adelaide, where they underwent emergency surgery.

In December 2022, the Modbury Heights mum pleaded not guilty to two charges of attempted murder due to mental incompetence.

But last October, Justice Sandi McDonald heard that Somerville would likely not contest the fact that she allegedly attacked her children, despite reports prepared by the defence concluding that she was mentally incompetent at the time.

Megan Jayne Somerville (pictured) has pleaded not guilty to the attempted murder of her two young sons

Megan Jayne Somerville (pictured) has pleaded not guilty to the attempted murder of her two young sons

Somerville (pictured) allegedly stabbed her two sons multiple times on the side of a motorway in 2022

Somerville (pictured) allegedly stabbed her two sons multiple times on the side of a motorway in 2022

Professor Jason White told the court on Monday that Somerville was believed to be a 'frequent' or 'daily drug user'.

Significant amounts of both illicit and prescription drugs were found in her system both 85 minutes and 14 hours after the alleged stabbings, the court heard. 

The tests found 0.39mg of methylamphetamine per litre of blood meaning it could have been as high as 0.43mg at 11.30pm.

'Methylamphetamine was detected in the blood sample, which is illicit in Australia. Amphetamine was also detected, that is both a therapeutic and an illicit drug,' Professor White told the court.

'... Therapeutic concentrations (of the drug) typically are in the range of .02 to .05, so (her results) were about ten times that.' 

'THC was also detected, which is the main active compound in cannabis.'

Somerville (pictured) claims she should not be found guilty of attempted murder due to her poor mental health at the time of the alleged attack

Somerville (pictured) claims she should not be found guilty of attempted murder due to her poor mental health at the time of the alleged attack

Somerville (pictured) appeared in Adelaide's Supreme Court via video link on Monday morning from a closed mental health facility

Somerville (pictured) appeared in Adelaide's Supreme Court via video link on Monday morning from a closed mental health facility

Prescribed antipsychotic medications were also detected.

Professor White believes the high concentration of drugs found in Somerville's system could have made her impulsive, confused, agitated, paranoid and obsessive.

He also concluded the drugs could have worsened an un underlying mental condition, like schizophrenia.

The court also heard that a friend had given evidence that of Somerville's had 'obtained' an '8-ball' of meth the night before the alleged attack. 

Justice McDonald will hear further evidence later this week.