When a young mother left her unit to buy groceries in NSW's Hunter Valley in 2005, she had no idea she would never see her 21-month-old son Jordan Thompson alive again.
Bernice Swales returned to find her child naked on a bed, with her then-boyfriend Cecil Kennedy attempting CPR.
She picked up Jordan and ran across the road to Singleton Hospital, stumbling and falling onto her elbows at times as his eyes "started to go to the back of his head", but he had no brain activity and was pronounced dead.
Mr Kennedy told police he left the toddler playing in the bath for 40 to 90 seconds and returned to find him face down.
But the toddler had been "deliberately administered" antidepressant medication by a "known" person and died as a consequence of the drug's toxicity, NSW Deputy State Coroner Elaine Truscott said on Friday.
Amitriptyline, contained in Endep antidepressant medication prescribed to Mr Kennedy, was found in the toddler's blood, liver, stomach and its contents following a post-mortem.
The "only rational explanation" for this was for Mr Kennedy to have given Jordan "at least one 50-milligram tablet" or its equivalent, probably in crushed form, the coroner said.
"I am unabletodefinitivelyfind what hismotivationwasfordoingso,althoughIconsider itlikelythat itwasdone toproduce asubduedorsedatedeffectinJordan ratherthanto cause permanent orlasting harm," she said.
Forensic evidence established Jordan ingested "at least 50 milligrams" of the drug on the morning of his death.
He vomited during the day and traces of Amitriptyline were later found in a stain on his tracksuit pants, in the bath water and in a nappy.
"I am satisfied that Jordan died as a consequence of Amitriptyline toxicity alone," Ms Truscott said.
"IdonotacceptthatJordan was foundsubmergedinthebathafterbeingleftthereplayingwiththecups."
The inquest was suspended in 2008 after a person was referred to the Director of Public Prosecutions, but in 2014 it was confirmed relevant charges had been withdrawn. The inquest resumed in 2015.
Outside court on Friday, Ms Swales said she had been reassured by NSW Police the investigation would continue.
"I'm very pleased with the outcome today. At least we have confirmed the actual cause of death now and that will enable us to move forward," she told reporters outside Glebe Coroners Court.
"I just remember him as happy, loving. He'll always be my little boy."
Ms Truscott recommended a protocol be created so blood samples can be authorised and taken from the deceased before they are transported to the Forensic Services, particularly "in the case of a child whose death is sudden, unexplained or not immediately apparent".
She made no referral to the DPP.
