Dominic Paterson, 21, of Blantyre, and 25-year-old Colin Campbell, of Bothwell, died suddenly in October last year.
As previously reported by the Evening Times, their bodies were discovered in the house in which Dominic lived with his mother, in Murray Crescent, Blantyre.
She is believed to have found the two men after returning home from a weekend away.
Post-mortem examinations were carried out on them, but the results were said to be inconclusive and further tests were carried out.
The Crown Office said its Scottish Fatalities Investigation Unit is now investigating the deaths.
Officially launched by the Lord Advocate in 2011, the unit provides expertise and specialist guidance on death investigations - especially those which raise issues of significant public concern.
In particular, the SFIU deals with more complex non-criminal cases.
Crown Office officials said Dominic and Colin's families would be kept up to date on any findings.
A spokesman for the Crown Office and Procurator Fiscal Service, said: "The Procurator Fiscal has received reports into the deaths of a 21-year-old male and a 25-year-old male in Blantyre, South Lanarkshire.
"The investigation into these deaths, under the direction of SFIU, is ongoing and the families will be kept updated in relation to any significant developments."
Hundreds of mourners attended the funerals of two friends, who were laid to rest in separate ceremonies, on the same day.
Dominic and Colin had been friends for many years and both had attended Holy Cross High School in Hamilton.
Dominic was a student at Motherwell College, while Colin had been planning to train for a job working offshore.