The heroin substitute methadone was implicated in more than half of the 90 drug-related deaths in the Lothians last year, with one charity warning the true number of lives lost through substance abuse is even higher.
Figures released by the General Register Office for Scotland revealed the number of fatalities across the region was the highest in five years and more than double that of 2002.
Methadone was implicated in 48 deaths, while heroin and morphine were factors in 19.
Benzodiazepines such as diazepam and temazepam – which can be prescribed by doctors – were implicated in 62 deaths, more than those involving illicit drugs only available from criminal dealers.
Experts remain divided on the use of methadone to treat long-term drug addiction.
Edinburgh University researcher Dr Roy Robertson, who is a GP in Muirhouse, said: “It’s always concerning that some individuals are dying from something that is meant to be a treatment.
“But a lot of deaths are not a result of methadone alone. People are using it in combination with alcohol, benzodiazepines and sometimes illegal drugs.
“And often it’s not being used by the people who it was prescribed to, it’s being given to a friend or purchased illegally.”
Carole Kelly, chief executive of Edinburgh-based charity Crew 2000, said the true number of deaths is likely to be higher because of a rise in the popularity of “legal highs” which may not be detectable in post mortems.
She said: “We’ve always said that a lot of drug deaths are unrecorded.
“That’s partly due to the increase of new psychoactive substances – or legal highs – in which it is very difficult to ascertain what a person has taken.
“The content of these products is often unknown and it’s very difficult to tell if a death has been caused by a legal high. It’s a problem that’s only set to get worse.”
Jim Sherval, specialist in public health with NHS Lothian, said while the number of drug-related deaths had risen over the last ten years, the increase could be put down to a number of factors including an ageing population of users.
He added: “Each drug-related death is a tragedy and can affect a great many people, including family, friends and those involved in the care of the person concerned.
“NHS Lothian has invested in additional services for drug users ranging from the introduction of the national naloxone programme to support the most vulnerable drug users , through to long-term support in primary care and the development of our abstinence-based community rehabilitation programme.
“We have improved access to specialist treatment and we work closely with our local authority partners through the alcohol and drug partnerships to provide specialised treatment, education and support.”