The number of drug-related deaths in Ireland is running at more than three times the officially recorded level, a new government report will reveal in November.

New figures collected by the National Drug-Related Deaths Index, set up by health minister Mary Harney in 2005 to record more accurately drug-related deaths, show that while 131 deaths were officially recorded in 2005 by the CSO's general mortality register, the new more in-depth method by the index puts the number at 400.

In the eight-year period between 1998 and 2005, the index found there were just under 2,500 drug related deaths in Ireland – over 300 a year. Official CSO figures have put the drug death rate at around 100 per year.

Of the 2,500 drug related deaths in eight years, over 1,500 were directly related to drugs. Heroin remains the main killer and was involved in over 60% of direct drug-related deaths. Cocaine was implicated in a little over one in 10 and while relatively small, the reports warns that cocaine-related deaths are on the increase.

The huge discrepancy between the two figures is due to the fact the CSO records only direct drug-related deaths or poisonings. The new NDRDI, however, included deaths indirectly attributed to drugs including, for example, a former drug user who died from hepatitis. One of the most startling figures in the survey reveals that of almost 350 deaths between 1998 and 2005 which were related to one drug, over 60 involved methadone.

The controversial heroin substitute, which has been prescribed in Ireland since the 1980s to help addicts off the killer drug, was also implicated in an additional 240 drug-related deaths where another drug was involved. The report says that a possible reason for this is that drug addicts are getting access to methadone from more than one source.

The report notes that the Department of Health is already looking into alternatives to methadone and is understood to be considering offering bupenorphine to patients instead.