A little boy who was found dead in his bed had drunk the heroin substitute methadone, police have confirmed.
Derek lived with his parents in the East Lothian village of Elphinstone
Two-year-old Derek Doran was found by his mother at his home in East Lothian on 13 December but test results have only just been received by police.
Officers said they were carrying out an inquiry into the circumstances surrounding the death in Elphinstone.
Derek's mother Lisa Dodds and his 22-year-old father Derek Doran have been questioned by officers.
The two-year-old was found by his mother, the Sunday Mail newspaper said.
He was taken to Edinburgh's Royal Hospital for Sick Children, where his death was confirmed.
Police said they received the results of a toxicology report last week, which confirmed Derek had died from a methadone overdose.
A police spokeswoman said: "We are investigating the death of a two-year-old child with a view to establishing the full circumstances.
"The death was reported to the procurator fiscal as all sudden deaths must be.
"We are working closely with our partner agencies to ensure a thorough investigation."
Annabel Goldie, leader of the Scottish Conservatives, said the young boy's death highlighted the need for a change of government policy on drug rehabilitation.
She called on the Scottish Executive to stop "parking" addicts on methadone.
Ms Goldie added: "Maybe now Labour and the Liberal Democrats will awake from their slumber and back our call for zero tolerance on drugs, properly resourced rehabilitation and an end to addicts being parked on methadone."
East Lothian Labour MSP John Home Robertson said he has already raised the problem on behalf of another parent, who lost a son in parallel circumstances.
He told BBC Scotland that the Scottish Executive must look at tightening controls on the way methadone is administered.
The boy was pronounced dead at the children's hospital in Edinburgh
He said: "It's meant to be a solution to a serious problem. It's meant to be a way to help heroin users get off a serious drug.
"But, I'm afraid it's become a problem in its own right. There's too much of it swilling around, because instead of being consumed by heroin users on the pharmacist's premises, it's being prescribed and taken off the premises."
A spokeswoman for the Scottish Executive said stricter procedures were being implemented following the inquiry into the case of serial killer Dr Harold Shipman.
She said: "Legislation is already being put in place to ensure much tighter monitoring of prescribing and dispensing of controlled drugs including methadone as a result of the Shipman Inquiry.
"If from the reports into this case there are recommendations or issues for prescribing policy we will not hesitate to address them."
In January it emerged that an 11-year-old girl was treated in hospital for the effects of heroin after she collapsed at school in Glasgow.
First Minister Jack McConnell has called for the carers involved in that case to be "held accountable".
His ministers have begun considering the removal of more children from drug addict parents following the case.