Earlier estimates suggested there were 30,000 people misusing drugs such as heroin, temazepam and cocaine.

But the new research, commissioned by the Scottish Executive, revealed that the figure is likely to be closer to 56,000.

However, the previous figure of 30,000 has been described as an "unscientific guesstimate" and the executive has moved to play down the difference in the figures.

Hepatitis C infections

The report is the first to try to provide estimates of the prevalence of problematic drug misuse and covers the year 2000.

It is based on research carried out by Glasgow University's Centre for Drug Misuse Research in conjunction with the Scottish Centre for Infection and Environmental Health.

The report suggests:

• there are an estimated 55,800 problematic drug misusers, equivalent to about 2% of the Scottish population aged between 15 and 54;

• of those users, an estimated 22,800 are injecting;

• by council area, the highest prevalence rates are in Glasgow (3.8%), Dundee City (3.5%) and Aberdeen (3%);

• the council areas with the highest prevalence rate among people aged 15 to 24 are Inverclyde (5.1%) and Aberdeen (4.7%);

• the problem was found in both urban and rural areas, but it was worse in urban areas;

• it is also thought that 10,000 injecting users have the hepatitis C virus.

Problematic drug misuse is defined as the use of opiates and substances like methadone.

The report was unveiled on Thursday by Deputy Justice Minister Iain Gray, who said that the emergence of a "clearer picture" would mean the problem can be better tackled.

Mr Gray said: "The executive is investing record amounts in tackling drug misuse.