Gemma Evans and Andrea Townsend deny the charges against them
The mother and half-sister of a teenage girl allegedly put her in bed and went to watch TV when they knew she had taken a heroin overdose, a court heard.
Carly Townsend, 16, died in the night at their Carmarthenshire home in May.
Andrea Townsend, 45, and Gemma Evans, 25, of Pwll, Llanelli, deny manslaughter through gross negligence.
The experienced drug users put her in the recovery position in bed and went to watch Emmerdale rather than call an ambulance, Swansea Crown Court heard.
It was claimed that during the day Carly, who had been taking heroin for two years, had injected the class A drug.
Paul Thomas QC, prosecuting, said she had been complaining about the symptoms of an overdose, including having a hot head and drifting in and out of consciousness.
He said that both her mother and half-sister knew she had taken heroin and were aware of the signs of an overdose.
Furthermore, he said, they knew how dangerous it could be as Ms Evans had suffered one before and Mrs Townsend's husband had died from an overdose of a different drug.
"They put her in the recovery position and left her in the bed," said Mr Thomas.
"They could see that 16-year-old Carly's lips had turned blue.
"Instead of calling for an ambulance, they went downstairs to watch the soaps on television."
Carly lay dying in her bedroom while her family watched television
Mr Thomas said the prosecution believed that Ms Evans had helped Carly to buy the drugs that killed her by acting as an intermediary.
He said that was the reason why they did not summon help.
"They feared that they themselves and or Carly would get into trouble," he said. "They took a risk with Carly's health that would cost her her life."
Police and paramedics were called to the house around 0900 BST on 3 May, where they found her dead in her bed.
The jury heard that Carly had recently served three months at the Hillside Secure Unit in Neath where she would have had no access to drugs so her tolerance would have been low.
Mr Thomas said it was the prosecution case that her mother and half-sister owed Carly a duty of care.
He said it was the prosecution case that their failure to provide this amounted to gross negligence.
The jury have been sent home for the weekend and the case will resume on Monday.