The controversial heroin substitute methadone improves the long-term survival of drug abusers, according to academics today.
A study showed the treatment reduced the frequency of drug use and led to a drop in the risk of death by 13% each year.
But the findings also showed the drug can prolong the number of years users continue to inject heroin.
Injecting can kill through overdose and the transmission of HIV and hepatitis. A recent outbreak of anthrax in Scotland caused 13 deaths among injecting users.
The research was carried out by the universities of Edinburgh, Bristol and Cambridge.
Roy Robertson, a GP who led the study at the University of Edinburgh, said: “Many injectors on a prescription will continue to occasionally inject, though may be reluctant to acknowledge this to their doctor for fear of a punitive response.
“Our research shows that despite this they still gain substantial health benefits from their prescription.
“Suggestions that methadone prescribing should be cut back or confined to the short-term are clearly misplaced and would lead to poorer health for drug injectors.”
The research comes three months after a group of 40 experts from around the world said methadone should be “readily available” to addicts seeking help.
They argued that scrapping the treatment could lead to a rise in crime and drug deaths.
But its use has been criticised by Scottish Conservatives, who claimed addicts are “parked” on methadone.
The Scottish Government’s drugs strategy aims to “support people to move on towards a drug-free life as active and contributing members of society”.
The new study suggests there is a “balance” between saving lives and achieving abstinence, researchers said.
Almost 800 people took part in the study, of whom 571 were still alive when research was followed up. At the end of that process, five more had died, bringing the total deaths to 228, or 29% of the group.
The study will be published by the British Medical Journal on July 17.